Secretins are among the largest bacterial outer membrane proteins known. Here we report the crystal structure of the periplasmic N-terminal domain of GspD (peri-GspD) from the type 2 secretion system (T2SS) secretin in complex with a nanobody, the VHH domain of a heavy-chain camelid antibody. Two different crystal forms contained the same compact peri-GspD:nanobody heterotetramer. The nanobody contacts peri-GspD mainly via CDR3 and framework residues. The peri-GspD structure reveals three subdomains, with the second and third subdomains exhibiting the KH fold which also occurs in ring-forming proteins of the type 3 secretion system. The first subdomain of GspD is related to domains in phage tail proteins and outer membrane TonB-dependent receptors. A dodecameric peri-GspD model is proposed in which a solvent-accessible β strand of the first subdomain interacts with secreted proteins and/or T2SS partner proteins by β strand complementation.
|Number of pages
|Published - Feb 13 2009
Bibliographical noteFunding Information:
We thank Stephen Moseley from the Department of Microbiology, University of Washington, for providing the ETEC genomic DNA, and the support staff of beamline BL9-2 of the SSRL for assistance during data collection. Portions of this research were carried out at the Stanford Synchrotron Radiation Laboratory, supported by the Department of Energy and by the NIH. We thank Nele Buys for the selection, expression, and purification of the nanobodies. This study was supported by National Institutes of Health grant AI34501 (to W.G.J.H.) and by the Belgian Government under the framework of the Interuniversity Attraction Poles (I.A.P. P6/19).
ASJC Scopus subject areas
- Structural Biology
- Molecular Biology