PilY1 and minor pilins form a complex priming the type IVa pilus in Myxococcus xanthus

Anke Treuner-Lange,Steffi Lindow,Georges Chreifi,Timo Glatter,Yi-Wei Chang,Grant J Jensen,Lotte Søgaard-Andersen,Marco Herfurth

doi:10.1038/s41467-020-18803-z

Abstract

Type IVa pili are ubiquitous and versatile bacterial cell surface filaments that undergo cycles of extension, adhesion and retraction powered by the cell-envelope spanning type IVa pilus machine (T4aPM). The overall architecture of the T4aPM and the location of 10 conserved core proteins within this architecture have been elucidated. Here, using genetics, cell biology, proteomics and cryo-electron tomography, we demonstrate that the PilY1 protein and four minor pilins, which are widely conserved in T4aP systems, are essential for pilus extension in Myxococcus xanthus and form a complex that is an integral part of the T4aPM. Moreover, these proteins are part of the extended pilus. Our data support a model whereby the PilY1/minor pilin complex functions as a priming complex in T4aPM for pilus extension, a tip complex in the extended pilus for adhesion, and a cork for terminating retraction to maintain a priming complex for the next round of extension.

Highlights

Type IVa pili are ubiquitous and versatile bacterial cell surface filaments that undergo cycles of extension, adhesion and retraction powered by the cell-envelope spanning type IVa pilus machine (T4aPM)
In Gram-negative bacteria, the T4aP machine (T4aPM) that underlies T4aP formation and function consists of at least ten conserved core proteins that localize to the outer membrane (OM), the periplasm, the inner membrane (IM), and the cytoplasm (Fig. 1a)
Based on intensity-based absolute quantification, which provide a proxy for absolute protein levels (“Methods”), these analyses revealed that PilA is one of the most abundant proteins in M. xanthus, while cluster_3 and cluster_1 proteins were much less abundant as previously reported for minor pilins in P. aeruginosa[5]

Summary

Introduction

Type IVa pili are ubiquitous and versatile bacterial cell surface filaments that undergo cycles of extension, adhesion and retraction powered by the cell-envelope spanning type IVa pilus machine (T4aPM). Among proteins known to be related to T4aP formation and function, three minor pilins (PilX3, PilW3, and FimU3) and the core T4aPM protein PilO, which is part of the lower periplasmic ring (Fig. 1a), were highly enriched in the PilY1.3-FLAG pull-down experiments (Fig. 3c and Supplementary Fig. 8a).

Results

Conclusion