Biology subjects

Rouger, Q.

Publications and source records attributed to Rouger, Q..

4 recordsLinked to original sources

bioRxiv2026

Conjugative pilus tip structure reveals convergence in secretion systems

Bacteria deploy specialised secretion systems to transfer proteins and DNA into other cells, driving microbial evolution, virulence and the spread of antibiotic resistance1. Among these, type IV secretion systems (T4SSs) are unique in mediating both effector delivery and conjugative DNA transfer via extracellular pili that establish contact with recipient cells2. How these molecular machines couple recipient-cell engagement to the opening of a secretion channel is a central unresolved question across direct-contact secretion systems. Here we present the first high-resolution structure of a conjugative pilus tip from the R388 T4SS. The tip comprises the major pilin VirB2 and the minor pilin VirB5 together with two unexpected components: VirB6, repositioned from the inner-membrane stalk to the pilus apex where it forms a dynamic gate, and KikA, a modular distal adhesin likely involved in recipient-cell engagement. These findings unify pilus biogenesis, entry exclusion and recipient-cell engagement into a single structural mechanism in which VirB6 acts as a gatekeeper that couples tip contact to channel opening, while KikA shapes a pointed adhesin at the apex. By comparing this architecture to the type III and type VI secretion systems, we reveal convergent gating and penetration principles to contact-dependent bacterial secretion.

molecular biology↗

bioRxiv2026

An internal scaffold supports microtubule architectural diversity in Xenopus spermatids

During spermiogenesis, early round spermatids differentiate into specialized spermatozoa through an extensive reshaping of the nucleus driven by coordinated cytoskeletal and chromatin-based mechanisms. In mammals, this process critically relies on the transient manchette, a microtubule-based structure that remodels the spermatid nucleus and serves a track to transport material required for flagellum assembly. However, the existence, organization, and molecular composition of such a structure in other vertebrates have remained poorly investigated. Here, we establish that an organized microtubule network is present in Xenopus spermatids and shares key architectural and molecular hallmarks of the mammalian manchette. We further uncover a large structural heterogeneity of spermatid microtubules, with variable protofilament numbers, skew angles, and lattice organizations. We reveal the presence of a Spaca9-Saxo2 internal scaffold in spermatid microtubules suggesting an internal reinforcement mechanism necessary for extensive nuclear reshaping and cytoplasm remodeling.

cell biology↗

bioRxiv2026

HInt: interaction-based homology discovery through accelerated genome-scale AlphaFold screening

Identifying homologous proteins across deep evolutionary distances remains a major challenge because sequence and structural similarity progressively become undetectable over time. Although protein-protein interactions (PPIs) are often constrained by function and evolution, whether conserved interaction interfaces can provide an independent signal for homology detection has remained largely unexplored owing to the computational cost of proteome-scale interaction prediction. Here we introduce HInt (Homology by Interaction), an accelerated AlphaFold-based framework that enables practical proteome-scale PPI prediction through biologically informed pre-filtering and optimised high-throughput structure modelling. Using HInt, we establish interaction-based similarity as a third axis of homology detection. We show that conserved interaction interfaces reveal homologous relationships that remain inaccessible to conventional sequence- and structure-based approaches. Application of HInt to both prokaryotic and eukaryotic systems, together with experimental validation, uncovered a previously unrecognised VirB5 pilus-tip protein in the F-plasmid type IV secretion system and a previously unannotated F-box-like protein in the Saccharomyces cerevisiae ubiquitin-proteasome system. By enabling practical proteome-scale interaction screening, HInt provides a general framework for uncovering hidden homologues and expands the conceptual landscape of protein homology inference.

molecular biology↗

bioRxiv2025

PPIFold: A Tool for Analysis of Protein-Protein Interaction from AlphaPullDown

Protein structure and protein-protein interaction (PPI) predictions based on coevolution have transformed structural biology, but managing pre-processing and post-processing can be complex and time-consuming, making these tools less accessible. Here, we introduce PPIFold, a pipeline built on the AlphaPulldown Python package, designed to automate file handling and streamline the generation of outputs, facilitating the interpretation of PPI prediction results. The pipeline was validated on the bacterial Type 4 Secretion System nanomachine, demonstrating its effectiveness in simplifying PPI analysis and enhancing accessibility for researchers.

bioinformatics↗