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Research article2010Peer reviewed

Conserved Hydrophobic Clusters on the Surface of the Caf1A Usher C-Terminal Domain Are Important for F1 Antigen Assembly

Dubnovitsky, Anatoly; Duck, Zoe; Härd, Torleif; MacIntyre, Sheila; Knight, Stefan David

Abstract

The outer membrane usher protein Caf1A of the plague pathogen Yersinia pestis is responsible for the assembly of a major surface antigen, the F1 capsule. The F1 capsule is mainly formed by thin linear polymers of CaF1 (capsular antigen fraction 1) protein subunits. The Caf1A usher promotes polymerization of subunits and secretion of growing polymers to the cell surface. The usher monomer (811 aa, 90.5 kDa) consists of a large transmembrane beta-barrel that forms a secretion channel and three soluble domains. The periplasmic N-terminal domain binds chaperone subunit complexes supplying new subunits for the growing fiber. The middle domain, which is structurally similar to Caf1 and other fimbrial subunits, serves as a plug that regulates the permeability of the usher. Here we describe the identification, characterization, and crystal structure of the Caf1A usher C-terminal domain (Caf1Ac). Caf1Ac is shown to be a periplasmic domain with a seven-stranded beta-barrel fold. Analysis of C-terminal truncation mutants of Caf1A demonstrated that the presence of CaF1 Ac is crucial for the function of the usher in vivo, but that it is not required for the initial binding of chaperone subunit complexes to the usher. Two clusters of conserved hydrophobic residues on the surface of Caf1Ac were found to be essential for the efficient assembly of surface polymers. These clusters are conserved between the FGL family and the FGS family of chaperone usher systems. (C) 2010 Elsevier Ltd. All rights reserved.

Keywords

assembly; chaperone-usher pathway; protein structure; secretion

Published in

Journal of Molecular Biology
2010, Volume: 403, number: 2, pages: 243-259
Publisher: ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD

      SLU Authors

    • Dubnovitsky, Anatoly

      • Department of Molecular Biology, Swedish University of Agricultural Sciences

      • Härd, Torleif

        • Department of Molecular Biology, Swedish University of Agricultural Sciences

        • Knight, Stefan David

          • Department of Molecular Biology, Swedish University of Agricultural Sciences

        UKÄ Subject classification

        Cell and Molecular Biology

        Publication identifier

        DOI: https://doi.org/10.1016/j.jmb.2010.08.034

        Permanent link to this page (URI)

        https://res.slu.se/id/publ/60671