Many Gram-negative bacteria use the multi-protein type II secretion system (T2SS) to selectively translocate virulence factors from the periplasmic space into the extracellular environment. In Vibrio cholerae the T2SS is called the extracellular protein secretion (Eps) system,which translocates cholera toxin and several enzymes in their folded state across the outer membrane. Five proteins of the T2SS, the pseudopilins, are thought to assemble into a pseudopilus, which may control the outer membrane pore EpsD, and participate in the active export of proteins in a "piston-like" manner. We report here the 2.0 Å resolution crystal structure of an N-terminally truncated variant of EpsH, a minor pseudopilin from Vibrio cholerae. While EpsH maintains an N-terminal α-helix and C-terminal β-sheet consistent with the type 4a pilin fold, structural comparisons reveal major differences between the minor pseudopilin EpsH and the major pseudopilin GspG from Klebsiella oxytoca: EpsH contains a large β-sheet in the variable domain, where GspG contains an α-helix. Most importantly, EpsH contains at its surface a hydrophobic crevice between its variable and conserved β-sheets, wherein a majority of the conserved residues within the EpsH family are clustered. In a tentative model of a T2SS pseudopilus with EpsH at its tip, the conserved crevice faces away from the helix axis. This conserved surface region may be critical for interacting with other proteins from the T2SS machinery.
|Number of pages||13|
|Journal||Journal of Molecular Biology|
|State||Published - Mar 14 2008|
Bibliographical noteFunding Information:
We acknowledge Stewart Turley for help with data collection, Brian Krumm for helpful discussions about crystallization, and Francis Athappilly for maintenance of our computing network. We thank Maria Sandkvist for advice, and the staff of beamline 9.2 at the SSRL, Stanford, for support during data collection. This research was supported by NIH grant AI34501 (to W.G.J.H.) from the National Institute of Allergy and Infectious Diseases, and by the Howard Hughes Medical Institute (HHMI).
- extra cellular protein secretion
- general secretion pathway
- type 4 Pilin biogenesis
ASJC Scopus subject areas
- Structural Biology
- Molecular Biology