Three-dimensional structure of the Neisseria meningitidis secretin PilQ determined from negative-stain transmission electron microscopy

J Bacteriol. 2003 Apr;185(8):2611-7. doi: 10.1128/JB.185.8.2611-2617.2003.

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Biological Transport
  • Fimbriae Proteins / metabolism
  • Fimbriae Proteins / ultrastructure*
  • Microscopy, Electron / methods
  • Neisseria meningitidis / metabolism*
  • Pili, Sex / metabolism
  • Staining and Labeling

Substances

  • pilQ protein, bacteria
  • Fimbriae Proteins