Biology subjects

Ritter, C.

Publications and source records attributed to Ritter, C..

14 recordsLinked to original sources

bioRxiv2026

Intrinsic flexibility of Type VII secretion central pore is required for substrate translocation

Mycobacteria have up to five distinct type VII secretion pathways that play diverse roles in the cell ranging from iron uptake to virulence. To date, high-resolution structures of a hexameric ring-like pore complex have only been determined for closely related mycobacterial ESX-5 systems. The most significant difference between them is the arrangement and flexibility of the inner transmembrane helices of the EccC5 subunit within the central pore, leading to either a closed or to a semi-open conformation of the pore. In this work, we probed the functional roles of several central pore-forming residues in mediating secretion and demonstrate their crucial role in ESX-5 substrate translocation efficiency. Structural characterization of an ESX-5 variant with a conserved proline (P73A) surprisingly revealed rigidification of the pore-forming helices. In summary, our data demonstrate that maintaining the conformational flexibility of the central ESX-5 pore is essential for substrate secretion. Our findings reveal how the rigid structural ESX-5 scaffold with separate sections - facing the periplasm, the inner mycobacterial cell wall membrane and facing the cytosol - provides a complex framework for a high level of pore dynamics, restricted to the inner EccC5 subunit pore-forming helices. Their proper integration is required to generate a functional secretion system. The high level of conservation of several pore-forming residues across different type VII secretion systems indicates our findings to be general valid for these systems. SIGNIFICANCE STATEMENTA key virulence signature of the deadliest pathogenic mycobacteria is the presence of a number of highly specialized the type-VII secretion systems, which translocate distinct infection-promoting proteins through a central pore. Recent high-resolution structures of one of these systems (ESX-5) have revealed closed or partially closed pore states. This raises the question of how pore opening is mediated to allow substrate transport. Here, we demonstrate that this system is highly sensitive to even subtle changes within the central pore. Loss of conformational pore flexibility impairs secretion. A comprehensive understanding on the structure and associated dynamics of the central pore of type-VII secretion systems is essential to further unraveling mycobacterial virulence and developing future strategies for combatting it.

microbiology↗

bioRxiv2025

Internally twin-Strep tagged CD63 for rapid and efficient isolation of engineered extracellular vesicles encapsulating functional proteins

Extracellular vesicles (EVs) are important mediators of intercellular communication. Achieving high purity of intact engineered EVs through separation from the overwhelming background of unmodified vesicles and cellular or serum-derived contaminants remains a major challenge, yet is critical for fundamental studies of EV biology and EV-based therapeutics. To address this unmet need, we applied structure-guided engineering to canonical EV tetraspanins. Focusing on CD63 and CD9, we identified sites for internal insertion of the twin-Strep tag via flexible linkers into unstructured regions of their large extracellular loops. This design retains functional properties of the scaffolds while providing a robust molecular handle enabling rapid, efficient, and selective antibody-free affinity-based isolation of intact EVs using advanced Strep technology. Fusing proteins of interest (POIs) to the C-terminus of these scaffolds, either directly or via a photoactivatable protein, allowed POI loading into the lumen of twin-Strep tagged EVs with optional optogenetic control of POI release. Proteomic analysis confirmed the high purity of captured engineered EVs with >96% of contaminants removed, enabling sensitive detection of numerous EV-associated proteins. We also report the efficient removal of contaminating virus particles resembling EVs in size and density. Purified engineered EVs successfully delivered an encapsulated fluorescent reporter into target cells, bypassing dye labeling commonly used to track EVs. We demonstrate endosomal escape of the reporter, facilitated by EV decoration with vesicular stomatitis virus glycoprotein, and cytoplasmic release upon optogenetic activation. Our toolbox may serve as a broadly applicable strategy for the efficient production of intact and highly pure engineered EVs to support potential fundamental or translational EV studies.

molecular biology↗

bioRxiv2025

Transient YAP/TAZ inhibition exposes therapeutic vulnerabilities in advanced cancers

YAP and TAZ, key effectors of the Hippo pathway, are frequently hyperactivated in cancer, where they drive tumor progression and resistance to therapy. Their oncogenic activity relies on interaction with TEAD transcription factors, making the TEAD-YAP/TAZ complex an attractive therapeutic target. Using translational mouse models, we demonstrate that sustained systemic YAP/TAZ depletion leads to severe side effects. However, even transient YAP/TAZ inhibition alone is sufficient to suppress tumor growth in advanced stages. Mechanistically, YAP/TAZ activity promotes T cell exclusion from the tumors by inducing target genes involved in tissue remodeling. Consequentially, YAP/TAZ inhibition induces immune infiltration, but the infiltrating T cells rapidly become exhausted. Combining YAP/TAZ inhibition with immune checkpoint blockade (ICB) overcomes this exhaustion and sensitizes previously resistant tumors to immunotherapy.

cancer biology↗

bioRxiv2024

Protective function of ex vivo expanded CD8 T cells in a mouse model of adoptive therapy for cytomegalovirus infection depends on integrin beta 1 but not CXCR3, CTLA4, or PD-1 expression

The adoptive transfer of virus-specific T cells (VSTs) represents a therapeutic option for viral infection treatment in immunocompromised patients. Before administration, ex vivo culture enables VST expansion. However, it is unclear how ex vivo expansion affects the circulation, homing, and intra-tissue migration of administered VSTs. We established a model of VST immunotherapy of acute cytomegalovirus infection using adoptive transfer of ex vivo expanded OT-I CD8 T cells (recognizing SIINFEKL peptide) into Rag2-/- mice infected with murine cytomegalovirus (MCMV) encoding for the SIINFEKL peptide. Ex vivo expansion induced an effector T cell phenotype and affected the expression of integrins and chemokine receptors. CRISPR/Cas9-mediated gene deletions enabled us to address the role of selected genes in the homing of VSTs following intravenous administration. We found that deletion of Itgb1, encoding for integrin beta 1, prevented OT-I cells from entering infected organs and drastically reduced their number in blood, suggesting that adoptively transferred VSTs primarily expand in the infected tissues. In contrast, Cxcr3-/- OT-I cells provided equal protection as their Cxcr3+/+ counterparts, indicating that this chemokine receptor does not contribute to VST entry into infected organs. Further, Pdcd1 and Ctla4 deletion did not impair the transferred OT-I cells ability to protect mice from MCMV, arguing against quick exhaustion of VSTs with an effector T cell phenotype. Together, these data indicate that ex vivo expansion affects migration and activation properties of VSTs and suggest that future clinical evaluation of adoptive T cell therapy efficacy should include homing molecule expression assessment.

immunology↗

bioRxiv2023

Structural insights into the RNA maturation of the mitoribosome by GTPBP10

Mitochondria contain their own genetic information and a dedicated translation system to express it. The mitochondrial ribosome is assembled from mitochondrial-encoded RNA and nuclear-encoded ribosomal proteins. Assembly is coordinated in the mitochondrial matrix by biogenesis factors that transiently associate with the maturing particle. Here, we present a structural snapshot of a previously unknown large mitoribosomal subunit assembly intermediate containing 7 biogenesis factors including the GTPases GTPBP7 and GTPBP10. Our structure illustrates how GTPBP10 aids the folding of the ribosomal RNA during the biogenesis process, how this process is related to bacterial ribosome biogenesis, and why mitochondria require 2 biogenesis factors in contrast to only 1 in bacteria.

biochemistry↗

bioRxiv2023

Elephants develop wrinkles through both form & function

The trunks of elephants have prominent wrinkles from their base to the very tip. But neither the obvious differences in wrinkles between elephant species nor their development have been studied before. Asian elephants have more dorsal major, meaning deep and wide, trunk wrinkles (~126 {+/-} 25 SD) than African elephants (~83 {+/-} 13 SD). Both species have more dorsal than ventral major trunk wrinkles and a closer wrinkle spacing distally than proximally. In Asian elephants wrinkle density is high in the trunk wrapping zone. Wrinkle numbers on the left and right sides of the distal trunk differed as a function of trunk lateralization, with frequent bending in one direction causing wrinkle formation. MicroCT-imaging and microscopy of newborn elephants trunks revealed a constant thickness of the putative epidermis, whereas the putative dermis shrinks in the wrinkle troughs. During fetal development wrinkle numbers double every 20 days in an early exponential phase. Later wrinkles are added slowly, but at a faster rate in Asian than African elephants. We characterize the lifelong development of trunk wrinkles in Asian and African elephants and discuss the relation of species differences in trunk wrinkle distribution and number with behavioral, environmental, genetic, and biomechanical factors.

physiology↗

bioRxiv2023

Replisome loading reduces chromatin motion independent of DNA synthesis

Chromatin has been shown to undergo diffusional motion, which is affected during gene transcription by RNA polymerase activity. However, the relationship between chromatin mobility and other genomic processes remains unclear. Hence, we set out to label the DNA directly in a sequence unbiased manner and followed labeled chromatin dynamics in interphase human cells expressing GFP-tagged PCNA, a cell cycle marker and core component of the DNA replication machinery. We detected decreased chromatin mobility during the S-phase compared to G1 and G2 phases in tumor as well as normal diploid cells using automated particle tracking. To gain insight into the dynamical organization of the genome during DNA replication, we determined labeled chromatin domain sizes and analyzed their motion in replicating cells. By correlating chromatin mobility proximal to the active sites of DNA synthesis, we showed that chromatin motion was locally constrained at the sites of DNA replication. Furthermore, inhibiting DNA synthesis led to increased loading of DNA polymerases. This was accompanied by accumulation of the single-stranded DNA binding protein on the chromatin and activation of DNA helicases further restricting local chromatin motion. We, therefore, propose that it is the loading of replisomes but not their catalytic activity that reduces the dynamics of replicating chromatin segments in the S-phase as well as their accessibility and probability of interactions with other genomic regions. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=76 SRC="FIGDIR/small/531331v2_ufig1.gif" ALT="Figure 1"> View larger version (35K): org.highwire.dtl.DTLVardef@ed9743org.highwire.dtl.DTLVardef@65c9d4org.highwire.dtl.DTLVardef@a583a7org.highwire.dtl.DTLVardef@6681b1_HPS_FORMAT_FIGEXP M_FIG C_FIG Highlights- Direct and sequence unbiased labeling of DNA genome-wide - DNA labeled chromatin is more mobile in G1/G2 relative to the S-phase - Restriction of chromatin motion occurs proximal to sites of DNA replication - Loading of replisomes, even in the absence of processive DNA synthesis, restricts chromatin motion

cell biology↗

bioRxiv2022

Endosomal egress and intercellular transmission of hepatic ApoE-containing lipoproteins and its exploitation by the hepatitis C virus

Liver-generated plasma Apolipoprotein E (ApoE)-containing lipoproteins (LPs) (ApoE-LPs) play central roles in lipid transport and metabolism. Perturbations of ApoE can result in several metabolic disorders and ApoE genotypes have been associated with multiple diseases. ApoE is synthesized at the endoplasmic reticulum and transported to the Golgi apparatus for LP assembly; however, ApoE-LPs transport from there to the plasma membrane is largely unknown. Here, we established an integrative imaging approach based on a fully functional fluorescently tagged ApoE. We found that ApoE-LPs accumulate in CD63-positive endosomes of hepatocytes. In addition, we observed the co-egress of ApoE-LPs and extracellular vesicles (EVs) along the late endosomal trafficking route. Moreover, complexes of ApoE-LPs and CD63-positive EVs were found to be transmitted from cell to cell. Given the important role of ApoE in viral infections, we studied the hepatitis C virus (HCV) and found that the viral replicase protein NS5A is enriched in ApoE-containing intraluminal vesicles. Interaction between NS5A and ApoE is required for the efficient release of EVs containing viral RNA. These vesicles are transported along the endosomal ApoE egress pathway. Taken together, our data argue for endosomal egress and transmission of hepatic ApoE-LPs, a pathway that is hijacked by HCV. Given the more general role of EV-mediated cell-to-cell communication, these insights provide new starting points for research into the pathophysiology of ApoE-related metabolic and infection-related disorders. Author SummaryThe post-Golgi egress pathway of hepatocyte-derived ApoE-containing lipoproteins (ApoE-LPs) is largely unknown. By using integrative imaging analyses, we show that ApoE-LPs are enriched in CD63-positive endosomes suggesting that these endosomes might be a central hub for the storage of ApoE-LPs from which they are released into the circulation. In addition, we provide evidence for the co-egress of ApoE-LPs with extracellular vesicles (EVs) along the late endosomal route and their transfer from cell to cell. This pathway is hijacked by the hepatitis C virus that induces the production of ApoE-associated EVs containing viral RNA. Given the important role of ApoE in multiple metabolic, degenerative and infectious diseases, and the role of EVs in cell-to-cell communication, these results provide important information how perturbations of ApoE might contribute to various pathophysiologies.

microbiology↗

bioRxiv2022

MHC class Ia molecules facilitate MCK2-dependent MCMV infection of macrophages and virus dissemination to the salivary gland

Murine cytomegalovirus (MCMV) infection of macrophages relies on MCMV-encoded chemokine 2 (MCK2) through one or more unknown cellular receptors while infection of fibroblast occurs independent of MCK2 and is mediated by cell-expressed neuropilin 1. Applying a CRISPR screen, we now identified that the MHC-Ia/Beta-2-microglobulin (B2m) complex serves as an entry port for MCK2-mediated infection of macrophages. Further analyses revealed that MCK2-dependent infection requires expression of the MHC-Ia haplotypes H-2b and H-2d but not H-2k. The importance of the MCK2-MHC-I-pathway for primary infection and viral dissemination was highlighted by experiments with B2m-deficient mice, which lack surface expression of MHC-I molecules. In those mice, intranasally administered MCK2-proficient MCMV could not infect alveolar macrophages and subsequently failed to disseminate into the salivary glands. The identified molecular pathway used by MCMV to infect lung resident macrophages provides essential knowledge for understanding cytomegalovirus-induced pathogenesis, tissue targeting, and virus dissemination.

immunology↗

bioRxiv2022

Differential elasticity in lineage segregation of embryonic stem cells

The question of what guides lineage segregation is central to development, where cellular differentiation leads to segregated cell populations destined for specialized functions. Here, using optical tweezers measurements of mouse embryonic stem cells (mESCs), we reveal a mechanical mechanism based on differential elasticity in the second lineage segregation of the embryonic inner cell mass into epiblast (EPI) cells - that will develop into the fetus - and primitive endoderm (PrE) - which will form extraembryonic structures such as the yolk sac. Remarkably, we find that these mechanical differences already occur during priming and not just after a cell has committed to differentiation. Specifically, we show that the mESCs are highly elastic compared to any other reported cell type and that the PrE cells are significantly more elastic than EPI-primed cells. Using a model of two cell types differing only in elasticity we show that differential elasticity alone can lead to segregation between cell types, suggesting that the mechanical attributes of the cells contribute to the segregation process. Our findings present differential elasticity as a previously unknown mechanical contributor to the lineage segregation during the embryo morphogenesis.

biophysics↗

bioRxiv2020

Structure of the mycobacterial ESX-5 Type VII Secretion System hexameric pore complex

To establish an infection, pathogenic mycobacteria use the Type VII secretion or ESX system to secrete virulence proteins across their cell envelope. The five ESX systems (ESX-1 to ESX-5) have evolved diverse functions in the cell, with the ESX-5 found almost exclusively in pathogens. Here we present a high-resolution cryo-electron microscopy structure of the hexameric ESX-5 Type VII secretion system. This 2.1 MDa membrane protein complex is built by a total of 30 subunits from six protomeric units, which are composed of the core components EccB5, EccC5, two copies of EccD5, and EccE5. The hexameric assembly of the overall ESX-5 complex is defined by specific inter-protomer interactions mediated by EccB5 and EccC5. The central transmembrane pore is formed by six pairs of EccC5 transmembrane helices that adopt a closed conformation in the absence of substrate in our structure. On the periplasmic face of the ESX-5 complex, we observe an extended arrangement of the six EccB5 subunits around a central cleft. Our structural findings provide molecular details of ESX-5 assembly and observations of the central secretion pore, which reveal insights into possible gating mechanisms used to regulate the transport of substrates.

microbiology↗

bioRxiv2019

The cerebellum is involved in processing of predictions and prediction errors in a fear conditioning paradigm

Prediction errors are thought to drive associative fear learning. Surprisingly little is known about the possible contribution of the cerebellum. To address this question, healthy participants underwent a differential fear conditioning paradigm during 7T magnetic resonance imaging. An event-related design allowed us to separate cerebellar fMRI signals related to the visual conditioned stimulus (CS) from signals related to the subsequent unconditioned stimulus (US; an aversive electric shock). We found significant activation of cerebellar lobules Crus I and VI bilaterally related to the CS+ compared to the CS-. Most importantly, significant activation of lobules Crus I and VI was also present during the unexpected omission of the US in unreinforced CS+ acquisition trials. This activation disappeared during extinction when US omission became expected. These findings provide evidence that the cerebellum has to be added to the neural network processing predictions and prediction errors in the emotional domain.

neuroscience↗

bioRxiv2018

Whole genome sequencing for drug resistance profile prediction in Mycobacterium tuberculosis

Whole genome sequencing allows rapid detection of drug-resistant M. tuberculosis isolates. However, high-quality data linking quantitative phenotypic drug susceptibility testing (DST) and genomic data have thus far been lacking.\n\nWe determined drug resistance profiles of 176 genetically diverse clinical M. tuberculosis isolates from Democratic Republic of the Congo, Ivory Coast, Peru, Thailand and Switzerland by quantitative phenotypic DST for 11 antituberculous drugs using the BD BACTEC MGIT 960 system and 7H10 agar dilution to generate a cross-validated phenotypic DST readout. We compared phenotypic drug susceptibility results with predicted drug resistance profiles inferred by whole genome sequencing.\n\nBoth phenotypic DST methods identically classified the strains into resistant/susceptible in 73-99% of the cases, depending on the drug. Changes in minimal inhibitory concentrations were readily explained by mutations identified by whole genome sequencing. Using the whole genome sequences we were able to predict quantitative drug resistance levels where wild type and mutant MIC distributions did not overlap. The utility of genome sequences to predict quantitative levels of drug resistance was partially limited due to incompletely understood mechanisms influencing the expression of phenotypic drug resistance. The overall sensitivity and specificity of whole genome-based DST were 86.8% and 94.5%, respectively.\n\nDespite some limitations, whole genome sequencing has high predictive power to infer resistance profiles without the need for time-consuming phenotypic methods.\n\nOne sentence summaryWhole genome sequencing of clinical M. tuberculosis isolates accurately predicts drug resistance profiles and may replace culture-based drug susceptibility testing in the future.

microbiology↗

bioRxiv2018

Planktonic Protist Biodiversity and Biogeography in Lakes From Four Brazilian River-Floodplain Systems

While the biodiversity and biogeography of protists inhabiting many ecosystems have been intensely studied using different sequencing approaches, tropical ecosystems are relatively under-studied. Here we sampled planktonic waters from 32 lakes associated with four different river-floodplains systems in Brazil, and sequenced the DNA using a metabarcoding approach with general eukaryotic primers. The lakes were dominated by the largely free-living Discoba (mostly the Euglenida) and Ciliophora unlike previously sampled Neotropical environments, bu the community similarities between samples were likewise low. These protists inhabiting these floodplains potentially form part of the large diversity of unknown diversity in the tropics.

microbiology↗