Journal of Bacteriology, July 2001, p. 3825-3832, Vol. 183, No. 13
0021-9193/01/$04.00+0 DOI: 10.1128/JB.183.13.3825-3832.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Department of Biomolecular Sciences, UMIST, Manchester, M60 1QD, United Kingdom,1 and Institute of Microbiology, Section of Molecular Microbiology, National Hospital, University of Oslo, N-0027 Oslo, Norway2
Received 1 February 2001/Accepted 10 April 2001
PilQ is a member of the secretin family of outer membrane proteins and is specifically involved in secretion of type IV pili in Neisseria meningitidis, Neisseria gonorrhoeae, and Pseudomonas aeruginosa. The quaternary structure of PilQ from N. meningitidis was analyzed by transmission electron microscopy by using a negative stain. Single particle averaging was carried out with a total data set of 650 individual particles, which produced a projection map generated from 296 particles at an estimated resolution of 2.6 nm. Oligomeric PilQ adopts a donut-like structure with an external ring that is 16.5 nm in diameter surrounding a central cavity that is 6.5 nm in diameter. Self-rotation and power spectrum analysis demonstrated the presence of 12-fold rotational symmetry, showing that PilQ is organized as a ring of 12 identical subunits. A model of the type IV meningococcal pilus fiber, based on the X-ray crystal structure of the N. gonorrhoeae pilin subunit, fitted neatly into the cavity, demonstrating how PilQ could serve as a channel for the growing pilus fiber.
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