Biology subjects

de Ru, A. H.

Publications and source records attributed to de Ru, A. H..

15 recordsLinked to original sources

bioRxiv2026

Identification of novel cellular intermediates unveils unique enzymes for flagellar glycan biosynthesis in Clostridioides difficile

Glycosylation of bacterial surface proteins, such as flagellin (FliC), is important for their function and is often involved in virulence of pathogens. Glycans can be further modified by so-called post-glycosylation modifications (PGMs) often resulting in exclusive molecular structures. In Clostridioides difficile a unique glycan structure (Type A) decorates FliC (which forms the flagellar filament) that consists of an O-linked N-acetyl-{beta}-D-glucosamine (GlcNAc) modified with an N-methyl-L-threonine via a phosphodiester linkage. This PGM is synthesized by a set of four enzymes encoded in one operon (ftaABCD), but the exact biosynthesis pathway and biosynthetic intermediates remain unknown. In this study, we chemically synthesized two hitherto undescribed biosynthetic intermediates that we predicted based on bioinformatic analyses, CDP-threonine and CDP-N-methylthreonine. We showed that they are involved in the Type A PGM biosynthesis, as evidenced by mass spectrometric analyses of extracts of a set of C. difficile mutant strains. Furthermore, we characterized FtaC to be a SAM-dependent CDP-threonine N-methyltransferase, that installs the methyl group on CDP-threonine prior to transfer of the PGM to GlcNAc-FliC, and we revealed FtaD as the CDP-N-methylthreonine:GlcNAc N-methylthreoninephosphotransferase. Finally, using recombinantly expressed FtaC and FtaD in combination with synthetic CDP-threonine, we reconstituted the biosynthesis pathway of the Type A PGM in vitro. Overall, our results open avenues to explore these unique biosynthesis enzymes in molecular detail to provide new points of entry for the development of biosynthesis inhibitors and tools to study the role of this PGM in virulence and flagellar assembly.

microbiology↗

bioRxiv2026

VAPB and its binding partner AKAP11 promote lipid droplet degradation

The endoplasmic reticulum (ER) is the master regulator of various cellular processes. To achieve its diverse functions, the ER interacts with other organelles at membrane contact sites, regions where organelles are brought into proximity. Most ER membrane contact sites are facilitated by the ER-resident VAP proteins. To address the role of VAP proteins in regulating cellular lipid homeostasis, we performed a targeted lipidomic screen after silencing individual VAPs. The loss of VAPB increases cellular levels of neutral lipids stored in lipid droplets (LDs). The increase in neutral lipids is reflected in the size, number and motility of LDs, and is due to the impaired degradation of these organelles. VAPB requires its contact site forming ability to regulate LDs, prompting the identification of protein kinase A (PKA) anchor AKAP11 as a VAPB interaction partner in regulating LD degradation and dynamics. Collectively, our findings identify a role for the ER-resident VAPB-AKAP11 interaction and PKA activity in regulating LD homeostasis. SummaryThe ER-resident membrane contact site protein VAPB and its interaction partner AKAP11 regulate lipid droplet size and motility by mediating neutral lipid degradation. VAPB requires its ability to form membrane contact sites and interact with AKAP11, protein kinase A anchor protein, for mediating lipid droplet homeostasis. This paper uncovers a role for VAPB-AKAP11-PKA axis in regulating the homeostasis of lipid droplets.

cell biology↗

bioRxiv2026

DNA end-resection is stimulated by an interaction between BRCA1 exon 11 and TOPBP1

Approximately 60% of the tumour suppressor protein BRCA1 is encoded by a single exon. Many tumours carry mutations in this exon, often resulting in exon skipping and thus a protein of a severely reduced size. Although none of the well-described protein domains of BRCA1 are encoded by this exon 11, the isoform lacking this part shows a hypomorphic activity in homologous recombination. To better understand the function of this large exon, we performed proteomic analyses to identify interaction partners via this part of the protein. Here, we report a DNA damage-and phospho-dependent interaction of TOPBP1 to the protein region of BRCA1 encoded by exon 11. Mechanistically, this interaction is required for BRCA1s role in end-resection during homologous recombination. In contrast, the interaction is not required for TOPBP1s role in ATR activation. Our data provide novel mechanistic insight into the function of this poorly characterized part of the BRCA1 protein.

molecular biology↗

bioRxiv2024

Vault RNAs aid viral infection by facilitating nuclear export of hnRNP C and ELAVL1

Vault RNAs (vtRNAs) are a family of four small non-coding RNAs (ncRNAs) that are ubiquitously expressed in many eukaryotes and that regulate multiple cellular pathways. Their expression is increased upon infection with various DNA and RNA viruses. This suggests they are either co-opted by the virus to aid replication or function as an antiviral restriction factor. However, their precise molecular function remains unclear. Here, we show that replication of picornaviruses, alphaviruses, and beta-coronaviruses broadly enhances vtRNA expression. We find that genetic loss of vtRNAs inhibits replication of Sindbis virus (SINV) and encephalomyocarditis virus (EMCV), independent of the antiviral type I interferon (IFN) response. A proteomic screen uncovered the vtRNA interactome and revealed that vtRNAs associate with RNA binding proteins ELAVL1 and hnRNP C in uninfected and infected cells. VtRNAs facilitate the translocation of ELAVL1 and hnRNP C from the nucleus to the cytoplasm in infected cells, an event that is required for efficient viral replication. Moreover, hnRNP C and ELAVL1 fail to associate with viral RNA in the cytosol of SINV-infected cells in the absence of vtRNAs. Together, our findings reveal a novel molecular mechanism by which vtRNAs exert proviral activity during the course of SINV and EMCV infection, which opens up new avenues for therapeutic targeting to fight infectious diseases.

molecular biology↗

bioRxiv2024

Elucidation of the glycan structure of the b-type flagellin of Pseudomonas aeruginosa PAO1

Flagella are essential for motility and pathogenicity in many bacteria. The main component of the flagellar filament, flagellin, often undergoes post-translational modifications, with glycosylation being a common occurrence. In Pseudomonas aeruginosa PAO1, the b-type flagellin is O-glycosylated with a structure that includes a rhamnose, a phospho-group and a previous unknown moiety. This structure resembles the well-characterized glycan (Type A) in Clostridioides difficile strain 630, which features an N-acetylglucosamine linked to an N-methylthreonine via a phosphodiester bond. This study aimed to characterize the b-type glycan structure in Pseudomonas aeruginosa PAO1 using a set of mass spectrometry experiments. For this purpose, we used wildtype P. aeruginosa PAO1 and several gene mutants from the b-type glycan biosynthetic cluster. Moreover, we compared the mass spectrometry characteristics of the b-type glycan with those of in vitro modified Type A-peptides from C. difficile strain 630{Delta}erm. Our results demonstrate that the thus far unknown moiety of the b-type glycan in P. aeruginosa consists of an N,N-dimethylthreonine. These data allowed us to refine our model of the flagellin glycan biosynthetic pathway in both P. aeruginosa PAO1 and C. difficile strain 630.

microbiology↗

bioRxiv2024

Non-prime- and Prime-side Profiling of Pro-Pro Endopeptidase Specificity Using Synthetic Combinatorial Peptide Libraries and Mass Spectrometry

A group of bacterial proteases, the Pro-Pro endopeptidases (PPEPs), possess the unique ability to hydrolyze proline-proline bonds in proteins. Since a proteases function is largely determined by its substrate specificity, methods that can extensively characterize substrate specificity are valuable tools for protease research. Previously, we achieved an in-depth characterization of PPEP prime-side specificity. However, PPEP specificity is also determined by the non-prime-side residues in the substrate. To gain a more complete insight into the determinants of PPEP specificity, we characterized the non-prime- and prime-side specificity of various PPEPs using a combination of synthetic combinatorial peptide libraries and mass spectrometry. With this approach, we deepened our understanding of the P3-P3 specificities of PPEP-1 and PPEP-2, while identifying PPEP-2s endogenous substrate as the most optimal substrate in our library data. Furthermore, by employing the library approach, we investigated the altered specificity of mutants of PPEP-1 and PPEP-2. Additionally, we characterized a novel PPEP from Anoxybacillus tepidamans, which we termed PPEP-4. Based on structural comparisons, we hypothesized that PPEP-4 displays a PPEP-1-like prime-side specificity, which was substantiated by the experimental data. Intriguingly, another putative PPEP from Clostridioides difficile, CD1597, did not display Pro-Pro endoproteolytic activity. Collectively, we characterized PPEP specificity in detail using our robust peptide library method and, together with additional structural information, provide more insight into the intricate mechanisms that govern protease specificity.

molecular biology↗

bioRxiv2024

Proteolytic activity of surface exposed HtrA determines its expression level and is needed to survive acidic conditions in Clostridioides difficile

To survive in the host, pathogenic bacteria need to be able to react to the unfavourable conditions that they encounter, like low pH, elevated temperatures, antimicrobial peptides and many more. These conditions may lead to unfolding of envelope proteins and this may be lethal. One of the mechanisms through which bacteria are able to survive these conditions is through the protease/foldase activity of the high temperature requirement A (HtrA) protein. The gut pathogen Clostridioides difficile encodes one HtrA homolog that is predicted to contain a membrane anchor and a single PDZ domain. The function of HtrA in C. difficile is hitherto unknown but previous work has shown that an insertional mutant of htrA displayed elevated toxin levels, less sporulation and decreased binding to target cells. Here, we show that HtrA is membrane associated and localized on the surface of C. difficile and characterize the requirements for proteolytic activity of recombinant soluble HtrA. In addition, we show that the level of HtrA in the bacteria heavily depends on its proteolytic activity. Finally, we show that proteolytic activity of HtrA is required for survival under acidic conditions.

microbiology↗

bioRxiv2023

AMPK activation induces RALDHhigh tolerogenic dendritic cells through rewiring of glucose and lipid metabolism

It is well known that dendritic cell (DC) activation and function are underpinned by profound changes in cellular metabolism. Several studies indicate that the ability of DCs to promote tolerance is dependent on catabolic metabolism. The AMP-activated kinase (AMPK) is a central nutrient and energy sensor whose activation promotes catabolism while inhibiting ATP-consuming anabolic pathways. Yet the contribution of AMPK activation to DC tolerogenicity remains unknown. Here, we show that AMPK activation renders human monocyte-derived DCs tolerogenic as evidenced by an enhanced ability to drive differentiation of regulatory T cells, a process dependent on increased RALDH activity. This is accompanied by a number of distinct metabolic changes, in particular increased breakdown of glycerophospholipids, enhanced mitochondrial fission-dependent fatty acid oxidation, and upregulated glucose catabolism. This metabolic rewiring is functionally important as we found interference with these metabolic processes to reduce to various degrees AMPK-induced RALDH activity as well as the tolerogenic capacity of moDCs. Altogether, our findings reveal a key role for AMPK signaling in shaping DC tolerogenicity, and suggest that AMPK may serve as new target to direct DC-driven immune responses in therapeutic settings.

immunology↗

bioRxiv2023

BRCA1/BARD1 ubiquitinates PCNA in unperturbed conditions to promote replication fork stability and continuous DNA synthesis.

Deficiencies in the BRCA1 tumor suppressor gene are the main cause of hereditary breast and ovarian cancer. BRCA1 is involved in the Homologous Recombination DNA repair pathway, and, together with BARD1, forms a heterodimer with ubiquitin E3 activity. The relevance of the BRCA1/BARD1 ubiquitin E3 activity for tumor suppression and DNA repair remains controversial and most efforts aimed to identify BRCA1/BARD1 ubiquitination substrates rely on indirect evidence. Here, we observed that the BRCA1/BARD1 ubiquitin E3 activity was not required for Homologous Recombination or resistance to Olaparib. Using TULIP2 methodology, which enables the direct identification of E3-specific ubiquitination substrates, we identified substrates for BRCA1/BARD1. We found that PCNA is ubiquitinated by BRCA1/BARD1 in unperturbed conditions independently of RAD18. PCNA ubiquitination by BRCA1/BARD1 avoids the formation of ssDNA gaps during DNA replication and promotes replication fork stability epistatically to BRCA1 S114 phosphorylation, addressing the controversy about the function of BRCA1/BARD1 E3 activity in Homologous Recombination.

molecular biology↗

bioRxiv2022

In-depth specificity profiling of Pro-Pro endopeptidases (PPEPs) using combinatorial synthetic peptide libraries

Proteases comprise the class of enzymes that catalyze the hydrolysis of peptide bonds, thereby playing a pivotal role in many aspects of life. The amino acids surrounding the scissile bond determine the susceptibility towards protease-mediated hydrolysis. A detailed understanding of the cleavage specificity of a protease can lead to the identification of its endogenous substrates, while it is also essential for the design of inhibitors. We developed a new method which combines the high diversity of a combinatorial synthetic peptide library with the sensitivity and detection power of mass spectrometry to determine protease cleavage specificity. We applied this method to study a group of bacterial metalloproteases that have the unique specificity to cleave between two prolines, i.e. Pro-Pro endopeptidases (PPEPs). We not only confirmed the prime-side specificity of PPEP-1 and PPEP-2, but also revealed some new unexpected peptide substrates. Moreover, we have characterized a new PPEP (PPEP-3) which has a prime-side specificity that is very different from that of the other two PPEPs. Importantly, the approach that we present in this study is generic and can be extended to investigate the specificity of other proteases.

biochemistry↗

bioRxiv2022

SUMO Activated Target Traps (SATTs) enable the identification of a comprehensive E3-specific SUMO proteome.

Ubiquitin and ubiquitin-like conjugation cascades consist of dedicated E1, E2 and E3 enzymes with E3s providing substrate specificity. Mass spectrometry-based approaches have enabled the identification of more than 60,000 acceptor sites for ubiquitin and 40,000 acceptor sites for SUMO2/3. However, E3-to-target wiring is poorly understood. The limited number of SUMO E3s provides the unique opportunity to systematically study E3-substrate wiring. We developed SUMO Activated Target Traps (SATTs) and systematically identified substrates for eight different SUMO E3s, PIAS1, PIAS2, PIAS3, PIAS4, NSMCE2, ZNF451, LAZSUL(ZNF451-3) and ZMIZ2. SATTs enabled us to identify 590 SUMO1 and 1195 SUMO2/3 targets in an E3-specific manner. We found pronounced E3 substrate preference, even at the substrate isoform level. Quantitative proteomics enabled us to measure substrate specificity of E3s, quantified using the SATT index. Furthermore, we developed the Polar SATTs web-based tool (https://amsterdamstudygroup.shinyapps.io/PolaRVolcaNoseR/) to browse the dataset in an interactive manner, increasing the accessibility of this resource for the community. Overall, we uncover E3-to-target wiring of 1681 SUMO substrates, highlighting unique and overlapping sets of substrates for eight different SUMO E3 ligases.

molecular biology↗

bioRxiv2021

Clostridioides difficile phosphoproteomics shows an expansion of phosphorylated proteins in stationary growth phase

Phosphorylation is a post-translational modification that can affect both house-keeping functions and virulence characteristics in bacterial pathogens. In the Gram-positive enteropathogen Clostridioides difficile the extent and nature of phosphorylation events is poorly characterized, though a protein-kinase mutant strain demonstrates pleiotropic phenotypes. Here, we used an immobilized metal affinity chromatography strategy to characterize serine, threonine and tyrosine phosphorylation in C. difficile. We find limited protein phosphorylation in the exponential growth phase but a sharp increase in the number of phosphopeptides after the onset of stationary growth phase. Among the overall more than 1500 phosphosites, our approach identifies expected targets and phosphorylation sites, including the protein kinase PrkC, the anti-sigma-F factor antagonist (SpoIIAA), the anti-sigma-B factor antagonist (RsbV) and HPr kinase/phosphorylase (HprK). Analysis of high-confidence phosphosites shows that phosphorylation on serine residues is most common, followed by threonine and tyrosine phosphorylation. This work forms the basis for a further investigation into the contributions of individual kinases to the overall phosphoproteome of C. difficile and the role of phosphorylation in C. difficile physiology and pathogenesis. ImportanceIn this manuscript, we present a comprehensive analysis of protein phosphorylation in the Gram-positive enteropathogen Clostridioides difficile. To date, only limited evidence on the role of phosphorylation in regulation in this organism has been published; the current study is expected to form the basis for research on this post-translational modification in C. difficile.

microbiology↗

bioRxiv2020

Healthy cells functionally present TAP-independent SSR1 peptides: implications for selection of clinically relevant antigens

Tumors with an impaired transporter associated with antigen processing (TAP) present several ER-derived self-antigens on HLA class I (HLA-I) which are absent on healthy cells. Selection of such TAP-independent antigens for T cell-based immunotherapy should include analysis of their expression on healthy cells to prevent therapy-induced adverse toxicities. However, it is unknown how the absence of clinically relevant antigens on healthy cells needs to be validated. Here we monitored TAP-independent antigen presentation on various healthy cells using a new toolbox consisting of a T cell clone recognizing a TAP-independent SSR1-derived antigen. We found that most but not all healthy cells present this antigen under normal and inflammatory conditions, indicating that TAP-independent antigen presentation is a variable phenomenon. Our data emphasize the necessity of extensive testing of a wide variety of healthy cell types to define clinically relevant TAP-independent antigens that can be safely targeted by immunotherapy.

immunology↗

bioRxiv2020

Site-specific glycosylation mapping of Fc gamma receptor IIIb from neutrophils of health donors

Fc gamma receptors (Fc{gamma}R) translate antigen-recognition by immunoglobulin G (IgG) into various immune responses. A better understanding of this key element of immunity promises novel insights into mechanisms of (auto-/allo-)immune diseases and more rationally designed antibody-based drugs. Glycosylation on both IgG and Fc{gamma}R impacts their interaction dramatically. In this study, we developed a straightforward and comprehensive analytical methodology to map Fc{gamma}RIIIb glycosylation from primary human material. In contrast to recently published alternatives, we assessed all glycosylation sites in a single LC-MS/MS run and simultaneously determined the donor allotype. Studying Fc{gamma}RIIIb derived from healthy donor neutrophils, we observed profound differences as compared to the soluble variant and the homologous Fc{gamma}RIIIa on natural killer cells. This method will allow assessment of Fc{gamma}RIII glycosylation differences between individuals, cell types, subcellular locations and pathophysiological conditions.

immunology↗

bioRxiv2020

PAKC: A novel Panel of HLA class I Antigen presentation machinery Knockout Cells from the same genetic origin

With the emergence of immunotherapies, the understanding of functional HLA class I antigen presentation to T cells is more relevant than ever. Current knowledge on antigen presentation is based on decades of research in a wide variety of cell types with varying antigen presentation machinery (APM) expression patterns, proteomes and HLA haplotypes. This diversity complicates the establishment of individual APM contributions to antigen generation, selection and presentation. Therefore, we generated a novel Panel of APM Knockout Cell lines (PAKC) from the same genetic origin. After CRISPR/Cas9 genome-editing of ten individual APM components in a human cell line, we derived clonal cell lines and confirmed their knockout status and phenotype. We then show how PAKC will accelerate research on the functional interplay between APM components and their role in antigen generation and presentation. This will lead to improved understanding of peptide-specific T cell responses in infection, cancer and autoimmunity. Key pointsO_LIWe generated a panel of cell lines to study HLA class I antigen presentation C_LIO_LIWe show how this will spark research in infection, tumor biology and autoimmunity C_LI

immunology↗