Biology subjects

Bergeron, J. R.

Publications and source records attributed to Bergeron, J. R..

3 recordsLinked to original sources

bioRxiv2024

The structure of the Tad pilus alignment complex reveals a periplasmic conduit for pilus extension

The Tad (Tight adherence) pilus is a bacterial appendage implicated in bacterial virulence, cell-cell aggregation, and biofilm formation. Despite its homology to the well-characterised Type IV pilus, the structure and assembly mechanism of the Tad pilus are poorly understood. Here, we investigate the role of the protein RcpC from Pseudomonas aeruginosa. Our analyses reveal that RcpC forms a dodecameric periplasmic complex, anchored to the inner membrane by a transmembrane helix, and interacting with the outer membrane secretin RcpA. We use single-particle Cryo-EM to elucidate the structure of this RcpC dodecamer, and cell-based assays to demonstrate that the RcpC-RcpA complex is essential for Tad-mediated cell-cell aggregation. Collectively, these data demonstrate that RcpC forms the Tad pilus alignment complex, which provides a conduit across the periplasm for the Tad pilus filament to access the extracellular milieu. Our experimental data and structure-based models allow us to propose a mechanism for Tad plus assembly.

microbiology↗

bioRxiv2024

Structure of the complete extracellular bacterial flagellum reveals mechanism for flagellin incorporation

The bacterial flagellum is essential for motility, adhesion, and colonization in pathogens like Salmonella enterica and Campylobacter jejuni. Its extracellular structure comprises the hook, hook-filament junction, filament, and filament cap. The native structures of the hook-filament junction and the cap remain elusive, leaving the molecular details of cap-mediated filament assembly largely uncharacterized. Here, we report the structure of the complete extracellular flagellum, encompassing the hook, hook-filament junction, filament, and cap. This structure reveals intermediates of filament assembly, providing a molecular blueprint for flagellin folding and insertion at the filament tip. Mutagenesis and functional assays demonstrate the crucial roles of the caps terminal regions in flagellin incorporation, and of the structural integrity of the hook-filament junction. Finally, the structure of the cap and hook-filament junction prior to filament assembly reveals the structural basis for the initiation of filament assembly. Collectively, this study provides comprehensive insights into flagellum assembly and how flagellin incorporation is coupled with its secretion.

microbiology↗

bioRxiv2021

The cryo-EM structure of the bacterial type I DNA segregation ATPase filament reveals its conformational plasticity upon DNA binding.

The efficient segregation of replicated genetic material is an essential step for cell division. In eukaryotic cells, sister chromatids are separated via the mitotic spindles. In contrast, bacterial cells use several evolutionarily-distinct genome segregation systems. The most common of these is the Type I Par system. It consists of an adapter protein, ParB, that binds to the DNA cargo via interaction with the parS DNA sequence; and an ATPase, ParA, that binds nonspecific DNA and mediates cargo transport. However, the molecular details of how this system functions are not well understood. Here, we report the cryo-EM structure of a ParA filament bound to its DNA template, using the chromosome 2 (Chr2) of Vibrio cholerae as a model system. We also report the crystal structures of this protein in various nucleotide states, which collectively offer insight into its conformational changes from dimerization through to DNA binding and filament assembly. Specifically, we show that the ParA dimer is stabilized by nucleotide binding, and forms a left-handed filament using DNA as a scaffold. Our structural analyses also reveal dramatic structural rearrangements upon DNA binding and filament assembly. Finally, we show that filament formation is controlled by nucleotide hydrolysis. Collectively, our data provide the structural basis for ParAs cooperative binding to DNA and the formation of high ParA density regions on the nucleoid, and suggest a role for its filament formation.

biophysics↗