Structure and Assembly of a Trans-Periplasmic Channel for Type IV Pili in Neisseria meningitidis

PLoS Pathogens

Stefan A. Frye¹  Tone Tønjum¹  Jeremy P. Derrick²  Richard F. Collins²  Tomas Adomavicius²  Robert C. Ford²  Jamie-Lee Berry²  Marie M. Phelan³  Lu-Yun Lian³  Louise Bird⁴  Ray Owens⁴ 

[1] Centre for Molecular Biology and Neuroscience, University of Oslo, Oslo, Norway;Faculty of Life Sciences, Michael Smith Building, University of Manchester, Manchester, United Kingdom;Institute of Integrative Biology, University of Liverpool, Liverpool, United Kingdom;Oxford Protein Production Facility, Research Complex at Harwell, Harwell, Oxford, United Kingdom

关键词: Secretin;    Secretion systems;    Neisseria meningitidis;    Pili;    fimbriae;    Oligomers;    Protein structure;    Sequence alignment;    Crystal structure;   

DOI  :  10.1371/journal.ppat.1002923

学科分类：生物科学（综合）

来源: Public Library of Science

【 摘 要 】

Type IV pili are polymeric fibers which protrude from the cell surface and play a critical role in adhesion and invasion by pathogenic bacteria. The secretion of pili across the periplasm and outer membrane is mediated by a specialized secretin protein, PilQ, but the way in which this large channel is formed is unknown. Using NMR, we derived the structures of the periplasmic domains from N. meningitidis PilQ: the N-terminus is shown to consist of two β-domains, which are unique to the type IV pilus-dependent secretins. The structure of the second β-domain revealed an eight-stranded β-sandwich structure which is a novel variant of the HSP20-like fold. The central part of PilQ consists of two α/β fold domains: the structure of the first of these is similar to domains from other secretins, but with an additional α-helix which links it to the second α/β domain. We also determined the structure of the entire PilQ dodecamer by cryoelectron microscopy: it forms a cage-like structure, enclosing a cavity which is approximately 55 Å in internal diameter at its largest extent. Specific regions were identified in the density map which corresponded to the individual PilQ domains: this allowed us to dock them into the cryoelectron microscopy density map, and hence reconstruct the entire PilQ assembly which spans the periplasm. We also show that the C-terminal domain from the lipoprotein PilP, which is essential for pilus assembly, binds specifically to the first α/β domain in PilQ and use NMR chemical shift mapping to generate a model for the PilP:PilQ complex. We conclude that passage of the pilus fiber requires disassembly of both the membrane-spanning and the β-domain regions in PilQ, and that PilP plays an important role in stabilising the PilQ assembly during secretion, through its anchorage in the inner membrane.

【 授权许可】

CC BY