title: Structure and assembly of a trans-periplasmic channel for type IV pili in Neisseria meningitidis.
abstract: 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.
authors.affiliation: Faculty of Life Sciences, Michael Smith Building, University of Manchester, Manchester, United Kingdom.
authors.forename: Jamie-Lee
authors.initials: JL
authors.lastname: Berry
authors.forename: Marie M
authors.initials: MM
authors.lastname: Phelan
authors.forename: Richard F
authors.initials: RF
authors.lastname: Collins
authors.forename: Tomas
authors.initials: T
authors.lastname: Adomavicius
authors.forename: Tone
authors.initials: T
authors.lastname: Tønjum
authors.forename: Stefan A
authors.initials: SA
authors.lastname: Frye
authors.forename: Louise
authors.initials: L
authors.lastname: Bird
authors.forename: Ray
authors.initials: R
authors.lastname: Owens
authors.forename: Robert C
authors.initials: RC
authors.lastname: Ford
authors.forename: Lu-Yun
authors.initials: LY
authors.lastname: Lian
authors.forename: Jeremy P
authors.initials: JP
authors.lastname: Derrick
mesh_terms: D001422:Bacterial Adhesion; D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D036781:Fimbriae Proteins / Q000737:chemistry / Q000378:metabolism*; D010861:Fimbriae, Bacterial / Q000378:metabolism* / Q000648:ultrastructure; D008958:Models, Molecular; D009345:Neisseria meningitidis / Q000378:metabolism* / Q000648:ultrastructure*; D019906:Nuclear Magnetic Resonance, Biomolecular; D019897:Periplasm / Q000378:metabolism; D011485:Protein Binding; D017510:Protein Folding; D017434:Protein Structure, Tertiary
chemical_list: D001425:Bacterial Outer Membrane Proteins; C084295:pilQ protein, bacteria; D036781:Fimbriae Proteins