Le Guenno, H. | bioRxiv Science

bioRxiv2023

Structure of a heteropolymeric type 4 pilus from a monoderm bacterium

Type 4 pili (T4P) are important virulence factors, which belong to a superfamily of nanomachines ubiquitous in prokaryotes, called type 4 filaments (T4F). T4F are defined as helical polymers of type 4 pilins. Recent advances in cryo-electron microscopy (cryo-EM) led to structures of several T4F. This revealed that the long N-terminal -helix, the trademark of pilins, packs in the centre of the filaments to form a hydrophobic core, which in bacteria is accompanied by the melting (unfolding) of a portion of 1. Since all available bacterial T4F structures are from diderm species, we tested whether this architecture is conserved in phylogenetically distant species by determining the structure of the T4P of the monoderm Streptococcus sanguinis. Our 3.7 A resolution cryo-EM structure of this heteropolymeric T4P, and the resulting full atomic model including all minor pilins, highlight universal features of bacterial T4F and have widespread implications in understanding their biology.

microbiology↗

bioRxiv2021

Dynamic proton-dependent motors power Type IX secretion and gliding adhesin movement in Flavobacterium

Motile bacteria usually rely on external apparatus like flagella for swimming or pili for twitching. By contrast, gliding bacteria do not rely on obvious surface appendages to move on solid surfaces. Flavobacterium johnsoniae and other bacteria in the Bacteroidetes phylum use adhesins whose movement on the cell surface supports motility. In F. johnsoniae, secretion and helicoidal motion of the main adhesin SprB are intimately linked and depend on the type IX secretion system (T9SS). Both processes necessitate the proton motive force (PMF), which is thought to fuel a molecular motor that comprises the GldL and GldM cytoplasmic membrane proteins. Here we show that F. johnsoniae gliding motility is powered by the pH gradient component of the PMF. We further delineate the interaction network between the GldLM transmembrane helices (TMH) and show that conserved glutamate residues in GldL TMH are essential for gliding motility, although having distinct roles in SprB secretion and motion. We then demonstrate that the PMF and GldL trigger conformational changes in the GldM periplasmic domain. We finally show that multiple GldLM complexes are distributed in the membrane suggesting that a network of motors may be present to move SprB along a helical path on the cell surface. Altogether, our results provide evidence that GldL and GldM assemble dynamic membrane channels that use the proton gradient to power both T9SS-dependent secretion of SprB and its motion at the cell surface.

microbiology↗