#bioRXiv

Ant abaecin-2 is a context-dependent copper-binding effector that can be either inhibitory or protective Host defense peptides (HDPs) are important components of the innate immune system that are used to combat pathogens and often rely on metal binding for their function. However, controlling trace nutrients such as transition metals may have other roles in host-symbiont interactions beyond poisoning harmful pathogens. This study characterizes the evolution, structural properties, and biochemical activity of the novel hymenopteran HDP abaecin-2. In myrmicine ants such as the fungus-growing tribe Attini, abaecin-2 has evolved to include an Amino-Terminal Cu(II) and Ni(II)-binding (ATCUN) motif, which we hypothesize may bind copper, a trace nutrient that is enriched in attine ant colonies. Combined results from mass spectrometry, competitive binding assays, circular dichroism, and NMR indicate that the abaecin-2 peptide lacks a defined secondary structure and can associate with up to 2 Cu(II) ions, one strongly bound at the ATCUN motif and another weakly bound, likely at a conserved histidine residue. Despite its copper-binding activity, abaecin-2 alone does not exhibit antibacterial activity against Escherichia coli or Bacillus subtilis (models for bacteria that live in ant fungus gardens). However, it synergizes with a model pore-forming peptide cecropin A to inhibit the growth of E. coli, similar to the related peptide abaecin-1. The copper-binding activity conferred by the ATCUN motif also protects copper-sensitive E. coli from excess copper toxicity. The dual, context-dependent inhibitory and protective roles we propose for abaecin-2 indicate that this previously under-characterized HDP may be used by attine ants to regulate both harmful and beneficial symbionts.

(BioRxiv All) Ant abaecin-2 is a context-dependent copper-binding effector that can be either inhibitory or protective: Host defense peptides (HDPs) are important components of the innate immune system that are used to combat pathogens and often rely on metal binding for their… #BioRxiv #MassSpecRSS

Structural and chemical properties of insects' chitin-containing extracellular matrices Insects' body barriers rely on specialized extracellular matrices that protect against harmful environmental influences. The outer barrier is the cuticle, which is composed of chitin, cuticle proteins and lipids. The peritrophic matrix (PM) serves as an inner barrier lining the midgut epithelium. It is composed of chitin fibers that are organized by PM proteins. While cuticle and PM proteins have received considerable attention in the past, supramolecular organization and physicochemical properties of the chitin component - particularly of the PM - remain poorly understood. Here, we combine synchrotron-based X-ray diffraction data from the PMs of lepidopteran and coleopteran insects with RNA interference (RNAi), mass spectrometric and histochemical analyses of the PM from Tribolium castaneum to determine chitins' allomorphic state and degree of acetylation. The chitin of the PM exhibits signatures characteristic of dihydrate {beta}-chitin along the entire midgut. In contrast, the cuticle is made of tightly packed -chitin nanofibrils. Mass spectrometry revealed that the PMs' chitin is highly acetylated (>95%). RNAi silencing of gut-specific genes encoding chitin deacetylasesTcCDA6-9 further increases the degree of acetylation. Histochemical analyses staining chitin with different degrees of acetylation confirm the predominance of highly acetylated chitin in the PM. Notably, the larval cuticle has a layered organization with deacetylated chitin present in exo- and highly acetylated chitin in endocuticles. Depletion of both TcCDA1 or TcCDA2 impairs chitin deacetylation, which indicates that both proteins cooperate in their activity in the integument. These results establish fundamental principles of polysaccharide-based extracellular matrices, with broad implications for insect biology.

(BioRxiv All) Structural and chemical properties of insects' chitin-containing extracellular matrices: Insects' body barriers rely on specialized extracellular matrices that protect against harmful environmental influences. The outer barrier is the cuticle, which is composed… #BioRxiv #MassSpecRSS

Cellular remodeling during photosymbiosis establishment revealed by single-cell dual proteomics Endosymbiosis of phytoplankton in heterotrophic hosts is ecologically important and has led to key evolutionary innovations. However, the dynamic molecular processes underlying endosymbiosis establishment remain poorly understood. Here, using large-particle sorting and liquid chromatography-tandem mass spectrometry, we unravel heterogeneous changes in proteomes of the cosmopolitan ciliate Paramecium and algal endosymbiont Chlorella from engulfment to stable endosymbiosis. The initial digestion sees a sharp decline of intracellular Chlorella cells, along with host cellular reorganization involving a reduction of the cortex-localized defensive organelles, trichocysts, and proteins for intracellular transport and recycling. The remaining Chlorella cells enter a bottleneck stage characterized by energy production and cell cycle commitment before active proliferation. Comparison of Paramecium with successful and failed endosymbiosis further identifies a solute carrier transporter that potentially mediates metabolic homeostasis of the endosymbiotic system. Our study reveals inter-organismal coordination during the transition from predator-prey to host-endosymbiont relationships. The approach of time-course single-cell dual proteomics can be useful for investigating diverse interactions between microbial eukaryotes.

(BioRxiv All) Cellular remodeling during photosymbiosis establishment revealed by single-cell dual proteomics: Endosymbiosis of phytoplankton in heterotrophic hosts is ecologically important and has led to key evolutionary innovations. However, the dynamic molecular processes… #BioRxiv #MassSpecRSS

SugarBase: mapping glycomolecule precursors in microbes Glycan biosynthesis relies on nucleotide-activated sugars, essential metabolites across all domains of life, yet their usage in microbes is poorly understood. Here we present SugarBase, a mass spectrometry and bioinformatic pipeline for untargeted exploration of microbial nucleotide sugar networks. SugarBase resolves the chemical complexity of microbial metabolism by combining narrow-window DIA fragmentation with a chemistry-informed parent ion identification algorithm. Applying SugarBase across a broad phylogenetic range of microbes revealed extensive, species-specific nucleotide sugar profiles, including many candidates with no existing annotation, generating the most comprehensive inventory of nucleotide sugars to date. SugarBase guided identification of gene clusters and allowed discrimination between pseudaminic- and legionaminic acid-producing strains, where genomic and proteomic data provided only ambiguous information. We resolved distinct nonulosonic acid profiles in several Campylobacter jejuni strains, sugars which may alter susceptibility towards distinct flagellotropic phages. We further identify previously undescribed CMP-activated higher-carbon ulosonic acids in Magnetospirillum, expanding the known chemical space in glycan biosynthesis. In summary, SugarBase supports scalable discovery of microbial nucleotide sugar pathways and enzymes, expanding access to chemically complex glycans and providing new targets for antimicrobial development.

(BioRxiv All) SugarBase: mapping glycomolecule precursors in microbes: Glycan biosynthesis relies on nucleotide-activated sugars, essential metabolites across all domains of life, yet their usage in microbes is poorly understood. Here we present SugarBase, a mass spectrometry… #BioRxiv #MassSpecRSS

diagFDR: Verifiable False Discovery Rate Reporting in Proteomics via Scope, Calibration, and Stability Diagnostics In mass spectrometry-based proteomics, false discovery rate (FDR) control underpins the credibility of peptide and protein identifications. In contemporary workflows, including multi-run Data Independent Acquisition (DIA), deep learning-assisted scoring, library-free searches, and extensive post-processing, the statement "1% FDR" has become increasingly ambiguous, potentially referring to different statistical entities, multiple-testing scopes, and null models. We propose a standardized framework requiring explicit specification of three complementary properties: "scope", meaning which statistical universe is controlled; "calibration", meaning whether confidence measures behave consistently with their intended interpretation on the reported unit; and "stability", meaning whether acceptance thresholds and resulting identification lists remain robust to perturbations. Building on routine target/decoy outputs, we introduce pipeline-agnostic diagnostics that audit internal coherence of scores, q-values, and posterior error probabilities, quantify tail support and cutoff fragility, and test plausibility of target-decoy assumptions. We further complement internal checks with external validation via entrapment, which measures empirical false positives on known absent sequences. We highlight a "granularity paradox": as scoring becomes more discriminative, decoy matches can become so sparse near stringent cutoffs that the numerical support for decoy-based estimation deteriorates, making reported FDR thresholds increasingly fragile despite improved separation between the distributions of target and decoy scores. Applications to DIA-NN and MS2Rescore show that scope and aggregation choices can materially alter both estimated error rates and list reproducibility. We provide a practical reporting checklist and an open-source R package (diagFDR, available from CRAN) that generates diagnostic reports from standard software outputs. As a minimal verifiable reporting standard, we recommend that any "FDR = alpha%" claim specify the controlled unit and scope, report tail support at the operating cutoff, and make decoy-inclusive outputs available for independent verification.

(BioRxiv All) diagFDR: Verifiable False Discovery Rate Reporting in Proteomics via Scope, Calibration, and Stability Diagnostics: In mass spectrometry-based proteomics, false discovery rate (FDR) control underpins the credibility of peptide and protein identifications. In… #BioRxiv #MassSpecRSS

Selective Hydrolytic Defluorination of Branched Perfluorooctanoic Acid Isomers by a Haloacid Dehalogenase Per- and polyfluoroalkyl substances (PFAS) are highly resistant to enzymatic C-F bond cleavage, and hydrolytic defluorination of long-chain PFAS has rarely been demonstrated. Here, we report selective hydrolytic defluorination of branched perfluorooctanoic acid (PFOA) isomers by a haloacid dehalogenase (4A) from Delftia acidovorans strain D4B. A fluoride-specific riboswitch biosensor was used for initial substrate screening, followed by scaled-up assays in which fluoride release was quantified using a fluoride ion-selective electrode. Defluorination products were subsequently identified by liquid chromatography-mass spectrometry (LC-MS). Although purified 4A (10 M) readily catalyzed hydrolytic defluorination of fluoroacetic acid, incubation of PFOA (0.5 mM) with purified 4A resulted in a statistically significant increase in fluoride release at elevated enzyme loading (500 M). High-resolution LC-MS/MS analysis revealed that defluorination products originated from minor branched PFOA isomers rather than linear PFOA. Molecular docking analyses supported catalytically plausible binding geometries for branched PFOA isomers, positioning the substrate -carbon within ~4 [A] of the catalytic aspartate residue. These findings demonstrate previously unrecognized hydrolytic reactivity of a haloacid dehalogenase toward branched PFAS isomers and expand the known catalytic scope of the haloacid dehalogenase family.

(BioRxiv All) Selective Hydrolytic Defluorination of Branched Perfluorooctanoic Acid Isomers by a Haloacid Dehalogenase: Per- and polyfluoroalkyl substances (PFAS) are highly resistant to enzymatic C-F bond cleavage, and hydrolytic defluorination of long-chain PFAS has rarely… #BioRxiv #MassSpecRSS

The inner nuclear membrane protein SUN1 regulates cullin-3 neddylation to maintain insulin signaling Metabolic dysfunction-associated steatotic liver disease (MASLD) is the most prevalent chronic liver disease and strongly linked to obesity and insulin resistance. We previously reported that the common nuclear envelope variant rs6461378 (g.842031C>T; SUN1 H118Y) associated with MASLD and related traits including insulin resistance. To gain insight into how wildtype (WT) and H118Y SUN1 might differentially impact insulin signaling, we performed affinity purification-mass spectrometry (AP-MS) in human liver-derived cells stably expressing WT or H118Y SUN1. Unbiased AP-MS revealed a novel SUN1-CUL3 interaction, with comparative analysis showing that WT SUN1 interacted robustly with CUL3, while CUL3 interaction was markedly diminished with H118Y SUN1. Cells in which SUN1 was silenced via siRNA, or in which H118Y SUN1 was ectopically expressed, showed increased CUL3 neddylation, which is required for cullin RING ligase (CRL)-mediated ubiquitination of insulin receptor substrate (IRS) proteins. Inhibition of neddylation restored IRS-1 levels and insulin signaling in H118Y SUN1-expressing cells. Together, our findings provide a potential mechanism of H118Y SUN1-driven insulin resistance and a viable therapeutic approach for its reversal.

(BioRxiv All) The inner nuclear membrane protein SUN1 regulates cullin-3 neddylation to maintain insulin signaling: Metabolic dysfunction-associated steatotic liver disease (MASLD) is the most prevalent chronic liver disease and strongly linked to obesity and insulin… #BioRxiv #MassSpecRSS

Boosting NADP-malic enzyme 1 enhances seed vigor and longevity in Arabidopsis thaliana Seed longevity is a key determinant of crop establishment, productivity, and germplasm conservation. During storage and germination, reactive oxygen species accumulate and contribute to seed aging through oxidative damage and loss of viability. The maintenance of redox homeostasis therefore relies on NADPH-dependent antioxidant systems, which require a continuous supply of reducing power. NADP-dependent malic enzyme 1 (NADP-ME1), represents a source of NADPH supporting antioxidant defense during seed aging. Here, we show that enhanced expression of NADP-ME1 positively contributes to seed vigor and longevity in Arabidopsis thaliana. NADP-ME1 overexpression lines exhibited faster germination and higher overall germination after accelerated aging, whereas knockout mutants showed markedly reduced germination performance. Enhanced post-aging vigor in the overexpression lines was associated with reduced oxidative damage as indicated by lower malondialdehyde and hydrogen peroxide accumulation, along with preservation of specific polyunsaturated fatty acids, and increased {gamma}-tocopherol levels in aged dry seeds. Enhanced expression of NADP-ME1 reshapes the transcriptome of germinated seeds under fresh conditions compared with the wild type, while only minimal differences between genotypes are detected in aged seeds. These results suggest that NADP-ME1 contributes to the establishment of a transcriptional state associated with enhanced seed vigor and improved post-aging germination. Finally, co-immunoprecipitation coupled to mass spectrometry and bimolecular fluorescence complementation identified aspartate aminotransferase 2 as a NADP-ME1 interactor, pointing to a link between malate metabolism and amino acid-related metabolic adjustment. Together, these results identify NADP-ME1 as a determinant of seed resilience to aging and a potential target for improving seed quality.

(BioRxiv All) Boosting NADP-malic enzyme 1 enhances seed vigor and longevity in Arabidopsis thaliana: Seed longevity is a key determinant of crop establishment, productivity, and germplasm conservation. During storage and germination, reactive oxygen species accumulate and… #BioRxiv #MassSpecRSS

An N-degron proteolytic pathway modulates recipient susceptibility to T6SS DNase effectors The type VI secretion system (T6SS) is a contractile nanoweapon widely employed by Gram-negative bacteria to gain competitive advantages by injecting effector proteins into recipient cells. Although the biochemical activities of T6SS effectors have been well characterized, how recipient factors modulate effector toxicity remains poorly understood. Using Agrobacterium C58 as a model, previous work identified the Escherichia coli ClpAP protease as a recipient susceptibility (RS) factor that enhances T6SS-mediated interbacterial competition. Agrobacterium C58 deploys two DNase effectors, Tde1 and Tde2, as the major antibacterial weapon. Here, we demonstrate that the recipient ClpAP protease and its adaptor ClpS enhanced C58-mediated interbacterial competition in a Tde2-dependent manner in both intra- and interspecies competition. Ectopic expression of Tde2 in E. coli caused growth inhibition and DNA cleavage in the presence of a functional ClpAPS protease complex, but not in any of the clpP, clpA or clpS mutants. Notably, Tde2 accumulated in these mutants but not in wild-type cells, whereas a catalytic variant accumulated regardless of ClpAPS status, suggesting that Tde2 is not directly degraded by ClpAPS. Instead, Tde2 depends on ClpAPS for full toxicity, likely through degradation of inhibitory N-degron substrate(s). Affinity purification of His-tagged Tde2 in a clpP mutant background, followed by mass spectrometry, identified eight N-degron substrate candidates. Tde2-mediated interbacterial competition was significantly reduced by overexpression of three candidates. Among them, the Tde2 DNase domain directly associated with guanosine 5'-monophosphate reductase GuaC, supporting a model in which Tde2 toxicity is blocked by binding of GuaC. Collectively, our findings reveal an unanticipated layer of recipient-mediated regulation in T6SS competition and highlight proteolytic control of inhibitory substrates as a determinant of bacterial susceptibility during interbacterial conflict.

(BioRxiv All) An N-degron proteolytic pathway modulates recipient susceptibility to T6SS DNase effectors: The type VI secretion system (T6SS) is a contractile nanoweapon widely employed by Gram-negative bacteria to gain competitive advantages by injecting effector proteins… #BioRxiv #MassSpecRSS

ARMH3 acts as a central scaffold at the Golgi/TGN through interactions with Arl5, GBF1, and PI4KB The armadillo repeat protein ARMH3 regulates the activity and localisation of the Golgi resident lipid kinase phosphatidylinositol 4 kinase III{beta} (PI4KB) and the Golgi-specific brefeldin A-resistance guanine nucleotide exchange factor 1 (GBF1) that activates Arf1. ARMH3 localises to the trans Golgi network (TGN) via the GTPase Arl5. We used hydrogen deuterium exchange mass spectrometry (HDX-MS) and AI-enabled modeling to define the interfaces of ARMH3 with its binding partners Arl5, PI4KB, and GBF1. The ARMH3-Arl5 interface was determined to consist of the N and C termini of ARMH3, with Arl5 binding causing conformational changes in ARMH3 located at a shared PI4KB/GBF1 interface. Both PI4KB and GBF1 form mutually exclusive complexes with ARMH3, with GBF1 binding to ARMH3 through a disordered loop we have named the ARMH3 binding region (ABR). The ARMH3 interfaces in PI4KB and GBF1 contain phosphosites, with the phosphomimetic mutation of GBF1 blocking complex formation. These findings provide new insights into the role of ARMH3 as a master coordinator of GTPase and phosphoinositide signaling at the Golgi/TGN.

(BioRxiv All) ARMH3 acts as a central scaffold at the Golgi/TGN through interactions with Arl5, GBF1, and PI4KB: The armadillo repeat protein ARMH3 regulates the activity and localisation of the Golgi resident lipid kinase phosphatidylinositol 4 kinase III{beta} (PI4KB) and… #BioRxiv #MassSpecRSS

Native entanglement misfolding contributes to age-associated structural changes across the Saccharomyces cerevisiae proteome Aging at the subcellular level involves the simultaneous decline in the cell's ability to maintain protein homeostasis and rise in misfolded proteins through a positive feedback loop. Here, we test if a widespread class of protein misfolding could contribute to proteome aging by examining if statistical associations exist between age-related changes in protein structure, measured by limited proteolysis mass spectrometry data of the aging Saccharomyces cerevisiae proteome, with structural annotations and molecular simulations. We find that globular proteins that are likely to exhibit entanglement misfolding are 121% more likely to exhibit age-related structural changes, and these changes are 59% more likely to be localized to natively entangled regions. Proteins containing native entanglements are seven-fold more likely to misfold, according to simulations, and populate long-lived, near-native misfolded states. Thus, the age-related structural changes in yeast proteins can be explained in part by the accumulation of misfolded proteins involving entanglements.

(BioRxiv All) Native entanglement misfolding contributes to age-associated structural changes across the Saccharomyces cerevisiae proteome: Aging at the subcellular level involves the simultaneous decline in the cell's ability to maintain protein homeostasis and rise in… #BioRxiv #MassSpecRSS

Detecting misfolded non-covalent lasso entanglements in protein structures, simulation trajectories, and mass spectrometry data A previously overlooked class of protein entanglements, non-covalent lasso entanglements (NCLEs), has been found to play a role in widespread protein misfolding. However, understanding the influence NCLEs have on biological processes is hindered by the absence of dedicated algorithms and computational tools to detect and characterize these geometries in protein structures, molecular dynamics simulations, and in comparison to experimental data from limited proteolysis (LiP) and cross-linking (XL) mass spectrometry (MS). Here, we present EntDetect, a software tool designed to: (1) identify non-redundant NCLEs in protein structures, (2) detect misfolded states by comparing NCLE changes through pairwise comparisons of structures, (3) extract structural ensembles consistent with experimental signals from LiP-MS and XL-MS, and (4) investigate proteome-wide protein misfolding using high-throughput MS data. We demonstrate the utility of EntDetect on a simulated structural ensemble of phosphoglycerate kinase (PGK), alongside corresponding LiP- and XL-MS experimental data. Additionally, we detail the application of EntDetect to detect misfolding associated with native NCLEs on a proteome-wide MS dataset and select candidate proteins for further investigation. This protocol is intended for biophysicists, structural biologists, and molecular biologists with domain knowledge of protein structure, mass spectrometry proteomics data, and beginner experience with Python who want to interpret their experimental observations and computer simulations results through the presence and potential misfolding of NCLE topologies. EntDetect is open-source and freely available (https://github.com/obrien-lab-psu/EntDetect). NCLEweb is also available which is a webserver that identifies NCLEs within a given user-uploaded structure (https://www.ncleweb.org/).

(BioRxiv All) Detecting misfolded non-covalent lasso entanglements in protein structures, simulation trajectories, and mass spectrometry data: A previously overlooked class of protein entanglements, non-covalent lasso entanglements (NCLEs), has been found to play a role in… #BioRxiv #MassSpecRSS

A low-cost rpoB-based multiplex MAMA PCR for differentiation of the Klebsiella pneumoniae species complex The Klebsiella pneumoniae species complex (KpSC) is a clinically important group of closely related pathogens associated with invasive infections. The complex comprises seven closely related members, which are often reported as K. pneumoniae, particularly in resource-limited settings. Accurate differentiation of KpSC members remains challenging because routine laboratory methods lack sufficient resolution, and approaches like mass spectrometry and whole genome sequencing (WGS) are not widely available. Consequently, the epidemiology and clinical significance of non-K. pneumoniae members of the KpSC remain underrecognized. We developed a conventional multiplex mismatch amplification mutation assay (MAMA) PCR targeting species- and subspecies-specific single-nucleotide polymorphisms in the housekeeping gene rpoB, with six primer sets for differentiation of common KpSC members. The assay was validated against 49 genomically characterized clinical isolates, after which 179 wastewater-derived isolates provisionally identified as Klebsiella spp. by standard microbiological methods were tested. Of these, 174 were assigned to specific KpSC members by the assay, while 5 produced inconclusive amplification patterns. A subset of 16 environmental isolates was selected for WGS, including four of the five inconclusive isolates. All environmental isolates with interpretable MAMA PCR patterns were concordant with WGS. The four inconclusive environmental isolates were identified as Enterobacter spp. Overall, comparison of MAMA PCR with WGS showed 100% sensitivity and 100% specificity for all tested targets, and the total cost was approximately US$1. This rpoB-based multiplex MAMA PCR provides a simple, accurate, and low-cost approach for differentiation of KpSC members in routine laboratories and may support improved identification and surveillance in resource-limited settings.

(BioRxiv All) A low-cost rpoB-based multiplex MAMA PCR for differentiation of the Klebsiella pneumoniae species complex: The Klebsiella pneumoniae species complex (KpSC) is a clinically important group of closely related pathogens associated with invasive infections. The… #BioRxiv #MassSpecRSS

Dynamic myosin 10 coupling to DCC and β1 integrin is mediated by intrinsically disordered regions during filopodial transport and patterning Intrinsically disordered regions (IDRs) are key mediators of protein-protein interactions. IDRs are important components of Myosin 10 (Myo10) and cargo complexes that influence neuronal development and cell growth, yet how IDRs dictate Myo10's cargo affinity and selectivity is not fully understood. Here, we investigate how the actin motor protein Myo10 engages two distinct cargo receptors, DCC and {beta}1 integrin, in cellular protrusions known as filopodia. Using hydrogen-deuterium exchange mass spectrometry (HDX-MS), cross-linking mass spectrometry (XL-MS), live-cell imaging, and super-resolution microscopy, we show that Myo10 decodes IDR elements through two complementary mechanisms: disorder-to-order transitions and "fuzzy" binding. The cytoplasmic portion of DCC binds Myo10 via a weakly helical P3 motif that acts as a preformed recognition element, while additional disordered motifs contribute to affinity through dynamic, weak interactions. In contrast, the {beta}1 integrin tail interacts with Myo10 through short NPxY motifs that remain disordered. Both cargos engage a common Myo10 surface but also contact distinct sites. Super-resolution DNA-PAINT imaging reveals distinct patterning of cargo with Myo10 along and around filopodia. Concentration measurements show that DCC is primarily bound while {beta}1 integrin exhibits a broader range of occupancy along the filopodial shaft. Multiple additive weak contacts and a shared binding site implies that DCC can out-compete integrin for Myo10 binding, which causes redistribution of active {beta}1 integrin from the filopodial tip to the shaft. Our findings illustrate a tunable, multivalent binding strategy that allows Myo10 to selectively coordinate diverse signaling cargos, demonstrating how regulated disorder within IDRs is one mechanism underlying cargo binding and cellular signaling.

(BioRxiv All) Dynamic myosin 10 coupling to DCC and β1 integrin is mediated by intrinsically disordered regions during filopodial transport and patterning: Intrinsically disordered regions (IDRs) are key mediators of protein-protein interactions. IDRs are important components… #BioRxiv #MassSpecRSS

PREPRINT ALERT🚨➡️Genetics influencing #epigenetics: Flanking DNA sequences influence #DNAmethylation maintenance 🧬

It’s been a minute because I needed a media break 🧘🏻‍♂️, but I couldn’t resist popping back for this: We just dropped a new #bioRxiv preprint 😃🤞🏻

BTW I’m looking for (academic) jobs

Using photoaffinity labelling to study pantothenamide uptake in malaria parasites Pantothenamides (PanAms) comprise a promising class of antimalarial compounds that kill asexual blood-stage Plasmodium falciparum parasites and block transmission. Intriguingly, the most advanced PanAm in drug development, MMV693183, is approximately 100 times more potent against female gametocytes than males. We hypothesized that this specificity is explained by a difference in PanAm uptake, which we studied using a PanAm-based photoaffinity labelling (PAL) probe. We successfully synthesized a probe that competed with MMV693183 in drug sensitivity assays, while the probe did not display high potency by itself. We observed no significant difference in median fluorophore-labelled probe signal intensity between male and female gametocytes, although there might be a difference in subcellular localization of the probe between the sexes. By combining PAL with affinity purification and mass spectrometry, we were not able to identify novel candidate PanAm transporters. We conclude that PAL provides evidence that differences in PanAm uptake do not underly differences in PanAm sensitivity between the gametocyte sexes.

(BioRxiv All) Using photoaffinity labelling to study pantothenamide uptake in malaria parasites: Pantothenamides (PanAms) comprise a promising class of antimalarial compounds that kill asexual blood-stage Plasmodium falciparum parasites and block transmission. Intriguingly,… #BioRxiv #MassSpecRSS

Pushing the limits of SCP: bacSCP, a proof-of-concept study to investigate heterogeneity of bacteria by single cell proteomics. Single-cell proteomics (SCP) has emerged as a powerful approach to quantify protein expression variability at cellular resolution, yet most state-of-the-art workflows are tailored to eukaryotic cells with only one study exploring how single bacteria can be analyzed by mass spectrometry. Here, we established bacSCP, a protocol extending SCP to bacterial cells, facing analytical challenges such as the thick bacterial cell wall hampering lysis, the extremely small cell size and resultant low protein content, and the consequently relatively high level of contaminating proteins from external sources. Using this bacSCP pipeline, we quantified more than 50 bacterial proteins from single Bacillus subtilis and Escherichia coli cells. Upon heat stress, we reproducibly observed up to 8-fold upregulation of chaperones including GroEL, GroES, and ClpC for a B. subtilis dmcsB strain. Importantly, single-cell measurements revealed potential heterogeneity within the heat-stressed subpopulation, enabling interrogation of stress-response variability at the proteome level. These results demonstrate the feasibility of bacSCP and provide a foundation for studying bacterial stress adaptation and phenotypic diversity with single-cell proteomic resolution.

(BioRxiv All) Pushing the limits of SCP: bacSCP, a proof-of-concept study to investigate heterogeneity of bacteria by single cell proteomics.: Single-cell proteomics (SCP) has emerged as a powerful approach to quantify protein expression variability at cellular resolution, yet… #BioRxiv #MassSpecRSS

Have you checked out our latest preprint in #bioRxiv: Uromodulin promotes immune zonation and inhibits alternative inflammasome-mediated activation of immune-to-collecting duct inflammatory signaling in early acute kidney injury?

www.biorxiv.org/content/10.6...

A Multi-Objective Scoring (MOS) Framework for Detecting Cross-Modal Spatial Similarity: Conceptual and Direct Formulations Spatial multi-omics methods allow researchers to study complex biological systems by integrating multiple molecular layers while preserving their spatial organization. However, integrating spatial transcriptomics and mass spectrometry imaging (MSI) remains challenging due to the differences between the two modalities, including sampling geometry, spatial resolution, signal scaling, and measurement principles. For example, 10x Genomics Visium captures transcriptomic data on a discrete hexagonal grid of spots; however, matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) produces dense Cartesian pixel maps of molecular distributions. These differences make exact spatial co-registration difficult and limit the effectiveness of single-metric similarity approaches. Here, we introduce a Multi-Objective Scoring (MOS) framework designed to detect cross-modal spatial similarity without requiring exact pixel-to-pixel alignment. The MOS framework integrates multiple complementary spatial descriptors into a unified similarity score, including coordinate-based metrics (value correlation, importance-based Intersection-over-Union (IoU), and importance-map correlation) and descriptor-based metrics that capture higher-order spatial organization, such as spatial histograms, radial profiles, quadrant statistics, and Moran's I spatial autocorrelation. These metrics are combined through a weighted ensemble model. This model calculates the weights using synthetic spatial datasets that simulate realistic tissue geometry, sampling differences, and spatial distortions. The framework was applied to a spatial multi-omics dataset from murine brain tissue, integrating spatial transcriptomics with MALDI-MSI lipidomics across young and aged control and Alzheimer's disease (AD) models. Synthetic data validation results demonstrated strong pattern-matching performance (96.14% accuracy), and application to experimental data identified several MSI analyte features whose spatial distributions closely matched transcriptomic patterns. In particular, strong and reproducible associations were observed between myelin-related genes (Mbp and Plp1) and multiple analyte features enriched in white matter regions. Overall, whether applied conceptually or directly, the MOS framework provides a strong strategy for cross-modal spatial integration and offers a scalable tool for discovering spatial relationships across diverse multi-omics datasets and facilitating hypothesis generation.

(BioRxiv All) A Multi-Objective Scoring (MOS) Framework for Detecting Cross-Modal Spatial Similarity: Conceptual and Direct Formulations: Spatial multi-omics methods allow researchers to study complex biological systems by integrating multiple molecular layers while preserving… #BioRxiv #MassSpecRSS

Proteomic mapping of novel tubulin post-translational modifications in Trypanosoma cruzi cytoskeleton Microtubules (MTs) play central roles in the organization and morphology of trypanosomatid parasites, forming highly specialized cytoskeletal structures such as the subpellicular corset, the flagellar axoneme, and the mitotic spindle. Functional specialization of MTs is regulated by the "tubulin code", which is defined by the combination of different - and {beta}-tubulin isotypes, a set of post-translational modifications (PTMs) and specific MT-binding proteins. Although multiple tubulin PTMs have been described in trypanosomatids using specific antibodies or mass spectrometry, to date no comprehensive mapping has been reported in Trypanosoma cruzi, the causative agent of Chagas Disease. In the present work, we performed a high-resolution proteomic analysis of PTMs present in - and {beta}-tubulin subunits of the T. cruzi Dm28c strain, using tubulin-enriched extracts obtained by in vitro polymerization. Multiple PTMs were identified, including acetylation, methylation, phosphorylation, and polyglutamylation, for which many modified amino acids had not been previously reported in trypanosomatids. Structural mapping of these modifications onto a predicted /{beta}-tubulin heterodimer showed that most modified residues are located in solvent-exposed regions of the protein. Together, these findings provide the first systematic map of tubulin PTMs in T. cruzi and support the existence of a complex tubulin code contributing to microtubule regulation in this parasite.

(BioRxiv All) Proteomic mapping of novel tubulin post-translational modifications in Trypanosoma cruzi cytoskeleton: Microtubules (MTs) play central roles in the organization and morphology of trypanosomatid parasites, forming highly specialized cytoskeletal structures such as… #BioRxiv #MassSpecRSS

Molecular dissection of protein complexes isolated from sections of human brain Molecular studies of brain receptors and transporters have typically relied on recombinant systems, limiting insight into their organization in native tissue. Here, we develop nanobody-based immunoprecipitation coupled with native mass spectrometry to interrogate endogenous protein assemblies from post-mortem mouse and human brain sections. We exemplify our approach by characterizing the synaptic proteins VGluT1 and mGluR2. From a single mouse brain, we discover mGluR2/3 heterodimers, alongside mGluR2 homodimers. Considering regions of human brain heterodimeric mGluR2/3 is highly abundant in the OFC and sgACC (~70% and 50%, respectively) and forms regional-specific interactions with additional synaptic proteins. In a modest cohort of biobanked human tissue, associated with depression and suicide, we find increased mGluR2/3 in the OFC. Consistent with this, mice exhibit similar associations between heterodimer levels and stress-susceptibility. Overall, our approach provides a direct means for establishing molecular-behavioural links at the level of receptor organization in brain.

(BioRxiv All) Molecular dissection of protein complexes isolated from sections of human brain: Molecular studies of brain receptors and transporters have typically relied on recombinant systems, limiting insight into their organization in native tissue. Here, we develop… #BioRxiv #MassSpecRSS

Enzymatic Ligation Strategy to Enhance Electrospray Ionization Efficiency and Liquid Chromatography-Mass Spectrometry of DNA and RNA Oligonucleotides Mass spectrometry (MS) is a powerful technique for characterizing modified RNA as it directly sequences and quantifies all mass-altering modifications simultaneously. However, the physicochemical properties of RNA result in poor ionization efficiencies during electrospray ionization, presenting a major barrier to sensitive MS measurements necessary for low abundance RNA samples and RNAs with low modification stoichiometries. Here, we report a ligation-based approach to increase ionization efficiencies of RNA oligonucleotides. We show that short (~5 nt), chemically modified DNA oligonucleotides can be enzymatically ligated to RNA to serve as MS signal enhancers. Among a series of signal enhancers appended with various alkyl and alkylimidazolium functional groups, we found that decyl-functionalized derivatives improved MS sensitivity by ~15-fold compared to unlabeled oligonucleotide. When ligated to RNA standards, the decyl-modified signal enhancer increased MS signals 2-4-fold with the additional benefit of improved retention during liquid chromatography (LC) separations without ion pairing agents. To apply the ligation-based approach to RNase T1 digests of longer RNAs, a multi-step enzymatic approach was optimized to maximize ligation efficiencies. We then ligated signal enhancers to a yeast transfer RNA (tRNA) digest and observed increased MS signals for numerous sequence-informative digestion products. Importantly, the sequences of RNA oligonucleotides ligated to signal enhancers were readily determined by tandem mass spectrometry with collision-induced dissociation. This ligation-based strategy for enhancing LC-MS/MS characterization of RNA creates opportunities to measure low abundance RNA samples and their modifications.

(BioRxiv All) Enzymatic Ligation Strategy to Enhance Electrospray Ionization Efficiency and Liquid Chromatography-Mass Spectrometry of DNA and RNA Oligonucleotides: Mass spectrometry (MS) is a powerful technique for characterizing modified RNA as it directly sequences and… #BioRxiv #MassSpecRSS

A Joint Promoterome-Proteome Atlas Highlights the Molecular Diversity of Human Skeletal Muscles More than 600 distinct skeletal muscles constitute up to 40% of the total mass of the human body. Human skeletal muscles differ in anatomical position, morphology, origin, and function, but the diversity of their molecular phenotypes, the gene expression and protein abundance profiles, remains poorly explored. Here, we report the large-scale CAGE-Seq promoterome profiling of 75 human skeletal muscles, complemented by 22 matched proteomes obtained with mass spectrometry. We identified 37001 transcribed regulatory elements and 1804 protein groups encompassing 1895 proteins, 80% of which demonstrated non-uniform expression across different muscles. The skeletal muscles of the eye, tongue, and diaphragm had the most distinctive molecular phenotypes, while the overall diversity was driven by hundreds of transcription factors with tissue-specific activity. By analyzing the allelic imbalance of CAGE-Seq reads, we discovered 6653 allele-specific single-nucleotide variants often coinciding with muscle-related GWAS SNPs, including muscle volume. Finally, we provide an interactive online atlas of transcriptomic and proteomic molecular phenotypes, facilitating further studies of gene regulation and heritable pathologies of skeletal muscles.

(BioRxiv All) A Joint Promoterome-Proteome Atlas Highlights the Molecular Diversity of Human Skeletal Muscles: More than 600 distinct skeletal muscles constitute up to 40% of the total mass of the human body. Human skeletal muscles differ in anatomical position, morphology,… #BioRxiv #MassSpecRSS

Stage-dependent tau post-translational modifications map the spatiotemporal progression of Alzheimer's disease Alzheimer's disease (AD) is defined by progressive tau aggregation, yet the molecular events driving this process remain poorly understood. Post-translational modifications (PTMs) are key regulators of tau biology and potential biomarkers of disease progression. Using immunoprecipitation-mass spectrometry and absolute quantification of tau isoforms, we profiled tau PTMs in soluble and insoluble brain fractions. We studied multiple brain regions (hippocampus, inferior temporal and frontal gyri), representing regions affected at different stages of pathology, from human donors spanning the AD spectrum and staged by ABC neuropathological scoring. We uncovered a stage-dependent PTM landscape across AD progression: early phosphorylation changes, including pT217 and pS262, precede later ubiquitination events, such as uK311, associated with tau aggregation. We also identified PTMs negatively correlated with aggregation, including mK258, suggesting potential protective roles. These findings refine our understanding of the spatiotemporal evolution of tau biochemistry and offer mechanistic and translational insights into AD tauopathy.

(BioRxiv All) Stage-dependent tau post-translational modifications map the spatiotemporal progression of Alzheimer's disease: Alzheimer's disease (AD) is defined by progressive tau aggregation, yet the molecular events driving this process remain poorly understood.… #BioRxiv #MassSpecRSS

🚨 New lab preprint alert! 🚨
A study 6 years in the making, made possible by @simonsfoundation.org support : "A multi-omic atlas in the African turquoise killifish reveals increased glucocorticoid signaling as a hallmark of brain aging" now on #biorXiv: www.biorxiv.org/content/10.6... A 🧵 1/11 🧪🖥️🧬

Statistical Principles Define an Open-Source Differential Analysis Workflow for Mass Spectrometry Imaging Experiments with Complex Designs Mass spectrometry imaging (MSI) characterizes the spatial heterogeneity of molecular abundances in biological samples. Experiments with complex designs, involving multiple conditions and multiple samples, provide particularly useful insight into differential abundance of analytes. However, analyses of these experiments require attention to details such as signal processing, selection of regions of interest, and statistical methodology. This manuscript contributes a statistical analysis workflow for detecting differentially abundant analytes in MSI experiments with complex designs. Using a case study of histologic samples of human tibial plateaus from knees of osteoarthritis patients and cadaveric controls, as well as simulated datasets, we illustrate the impact of the analysis decisions. We illustrate the importance of signal processing and feature aggregation for preserving biological relevance and alleviating the stringency of multiple testing. We further demonstrate the importance of selecting regions of interest in ways that are compatible with differential analysis. Finally, we contrast several common statistical models for differential analysis, showcase the appropriate use of replication, and demonstrate model-based calculation of sample size for followup investigations. The discussion is accompanied by detailed recommendations and an open-source R-based implementation that can be followed by other investigations.

(BioRxiv All) Statistical Principles Define an Open-Source Differential Analysis Workflow for Mass Spectrometry Imaging Experiments with Complex Designs: Mass spectrometry imaging (MSI) characterizes the spatial heterogeneity of molecular abundances in biological samples.… #BioRxiv #MassSpecRSS

Deep learning enables direct HLA typing from immunopeptidomics data The immune system eliminates malignant and infected cells through T-cell-mediated recognition of peptides presented by human leukocyte antigen molecules. Mass spectrometry-based immunopeptidomics enables unbiased identification of naturally presented HLA-restricted peptides and has become central to the development of T-cell-based immunotherapies. However, immunopeptidomics data reflects the combined peptide presentation of multiple HLA alleles, and determining which allotypes are represented in this multi-allelic complexity remains an unmet computational challenge. Here, we introduce immunotype, a deep learning-based ensemble predictor for HLA class I allotyping directly from immunopeptidomics data. Immunotype integrates peptide and HLA sequence information through transformer encoders and a graph neural network, complemented by a curated mono-allelic reference of known peptide-HLA binding preferences. Immunotype achieves an overall accuracy of 87.2% at protein-level resolution across diverse tissues and thereby enables rapid, cost-effective HLA typing of large-scale immunopeptidomics datasets.

(BioRxiv All) Deep learning enables direct HLA typing from immunopeptidomics data: The immune system eliminates malignant and infected cells through T-cell-mediated recognition of peptides presented by human leukocyte antigen molecules. Mass spectrometry-based… #BioRxiv #MassSpecRSS

Critical amino acid residues in the N-terminal domain of NADPH-dependent assimilatory sulfite reductase flavoprotein mediate octameric assembly How large, flexible enzymes assemble into defined oligomeric architectures remains a central question in biology. NADPH-dependent assimilatory sulfite reductase (SiR) forms a heterododecamer built on an octameric flavoprotein (SiRFP) core, yet the molecular basis for this assembly has been unresolved because of its disordered N-terminus. Here, we use ion mobility mass spectrometry, small-angle neutron scattering, and mutagenesis to define the mechanism of SiRFP oligomerization. We show that SiRFP forms a discrete, stable octamer in solution. We also report that its N-terminal 52-residue segment is necessary and sufficient to mediate assembly, also mediating oligomerization when fused to a heterologous protein. Structure-guided mutagenesis identifies four residues (Gln22, Tyr39, Phe40, and Gln47) whose substitution disrupts the octamer, producing concentration-dependent lower-order species while retaining catalytic activity. These findings define the determinants of SiRFP assembly with broader implications for engineering homomeric protein complexes.

(BioRxiv All) Critical amino acid residues in the N-terminal domain of NADPH-dependent assimilatory sulfite reductase flavoprotein mediate octameric assembly: How large, flexible enzymes assemble into defined oligomeric architectures remains a central question in biology.… #BioRxiv #MassSpecRSS

Comparison of Extraction Methods for the Quantification of Phytohormones from Tomato Fruits and Leaves by LC-MS/MS Accurate, simultaneous, and efficient quantification of chemically diverse phytohormone species is a critical task towards understanding the complex system of phytohormone signaling pathways. Quantification of phytohormones with the commonly used technique liquid chromatography coupled to tandem mass spectrometry is susceptible to the influence of non-phytohormone components present in the sample, a phenomenon referred to as matrix effect. To reduce matrix effect, some phytohormone quantification methods include additional steps of cleanup of crude extracts. However, to what extent additional purification steps provide increased accuracy compared to simpler, less laborious methods is seldomly evaluated. We evaluated three previously described phytohormone extraction methods, two of which include solid-phase extraction and one that does not, in their ability to minimize matrix effect and generate accurate estimates of phytohormone species spanning six classifications, from fruit and leaf tissue of Solanum lycopersicum cv. Micro-Tom (tomato). Our results show that, while the methods that included solid phase extraction occasionally outperformed each other regarding matrix effect and/or recovery efficiency for broad range of phytohormones, they rarely outperformed the simpler single-phase extraction method.

(BioRxiv All) Comparison of Extraction Methods for the Quantification of Phytohormones from Tomato Fruits and Leaves by LC-MS/MS: Accurate, simultaneous, and efficient quantification of chemically diverse phytohormone species is a critical task towards understanding the… #BioRxiv #MassSpecRSS

Soil bacterium Massilia secretes metabolites that promote Leptospira growth Understanding pathogen metabolism is critical for identifying key functions for drug targeting, establishing effective in vitro experimental systems, etc., particularly for metabolically unique organisms such as Leptospira. Pathogenic Leptospira are thought to infect humans from environmental sources; however, direct isolation from environmental samples remains technically challenging and is not yet well established. Here, we report that a ubiquitous environmental bacterium, Massilia sp., produces metabolites that promote the growth of Leptospira interrogans, encountered through an incidental contamination event, and identified in this study. Gas chromatography-tandem mass spectrometry (GC-MS/MS) analysis showed demonstrated that cultivating of Massilia sp. in R2A medium resulted in the accumulation of metabolites, including branched-chain amino acid (BCAA) intermediates, compared to fresh medium. By combining genome-scale metabolic modeling with experimental validation using cell-free culture supernatant supplementation assays, we demonstrate that BCAA intermediates, particularly 2-ketoisocaproic acid (4-methyl-2-oxopentanoate; 4MOP), a leucine biosynthetic intermediate produced by Massilia sp., enhance Leptospira growth. To investigate the metabolic role of 4MOP, we incorporated transcriptomic data into a genome-scale metabolic network model to generate condition-specific models. Resulted flux distributions indicated that Leptospiracatabolized imported 4MOP to produce acetyl-CoA. Our results reveal a previously unrecognized metabolic interaction where metabolites produced by environmental bacteria support the growth of pathogenic Leptospira, offering mechanistic insight into its metabolic requirement. These findings have implications to understand the environmental persistence of Leptospira through its metabolic dependencies on coexisting microbes, and they also help develop better strategies for this pathogen.

(BioRxiv All) Soil bacterium Massilia secretes metabolites that promote Leptospira growth: Understanding pathogen metabolism is critical for identifying key functions for drug targeting, establishing effective in vitro experimental systems, etc., particularly for metabolically… #BioRxiv #MassSpecRSS