title: Three-dimensional structure of the Neisseria meningitidis secretin PilQ determined from negative-stain transmission electron microscopy.
abstract: The PilQ secretin from the pathogenic bacterium Neisseria meningitidis is an integral outer membrane protein complex which plays a crucial role in the biogenesis of type IV pili. We present here the first three-dimensional structure of this type of secretin at 2.5-nm resolution, obtained by single-particle averaging methods applied to the purified protein complex visualized in a negative stain. In projection, the PilQ complex is circular, with a donut-like appearance. When viewed from the side it has a rounded, conical profile. The complex was demonstrated to have 12-fold rotational symmetry, and this property was used to improve the quality of the density map by symmetry averaging. The dominant feature of the structure is a cavity, 10 nm deep, within the center of the molecule. The cavity is funnel-shaped in cross section, measures 6.5 nm in diameter at the top of the complex, and tapers to a closed point, effectively blocking formation of a continuous pore through the PilQ complex. These results suggest that the complex would have to undergo a conformational change in order to accommodate an assembled pilus fiber of diameter 6.5 nm running through the outer membrane.
authors.affiliation: Department of Biomolecular Sciences, UMIST, Manchester M60 1QD, United Kingdom.
authors.forename: Richard F
authors.initials: RF
authors.lastname: Collins
authors.forename: Robert C
authors.initials: RC
authors.lastname: Ford
authors.forename: Ashraf
authors.initials: A
authors.lastname: Kitmitto
authors.forename: Ranveig O
authors.initials: RO
authors.lastname: Olsen
authors.forename: Tone
authors.initials: T
authors.lastname: Tønjum
authors.forename: Jeremy P
authors.initials: JP
authors.lastname: Derrick
mesh_terms: D001692:Biological Transport; D036781:Fimbriae Proteins / Q000378:metabolism / Q000648:ultrastructure*; D008854:Microscopy, Electron / Q000379:methods; D009345:Neisseria meningitidis / Q000378:metabolism*; D018933:Pili, Sex / Q000378:metabolism; D013194:Staining and Labeling
chemical_list: C084295:pilQ protein, bacteria; D036781:Fimbriae Proteins