Structural and Functional Studies on the N-terminal Domain of the Shigella Type III Secretion Protein MxiG

Journal article

MxiG is a single-pass membrane protein that oligomerizes within the inner membrane ring of the Shigella flexneri type III secretion system (T3SS). The MxiG N-terminal domain (MxiG-N) is the predominant cytoplasmic structure; however, its role in T3SS assembly and secretion is largely uncharacterized. We have determined the solution structure of MxiG-N residues 6-112 (MxiG-N(6-112)), representing the first published structure of this T3SS domain. The structure shows strong structural homology to forkhead-associated (FHA) domains. Canonically, these cell-signaling modules bind phosphothreonine (Thr(P)) via highly conserved residues. However, the putative phosphate-binding pocket of MxiG-N(6-112) does not align with other FHA domain structures or interact with Thr(P). Furthermore, mutagenesis of potential phosphate-binding residues has no effect on S. flexneri T3SS assembly and function. Therefore, MxiG-N has a novel function for an FHA domain. Positioning of MxiG-N(6-112) within the EM density of the S. flexneri needle complex gives insight into the ambiguous stoichiometry of the T3SS, supporting models with 24 MxiG subunits in the inner membrane ring. © 2011 by The American Society for Biochemistry and Molecular Biology, Inc.

Authors: McDowell, M; Johnson, S; Deane, J; Cheung, M; Roehrich, A

• Publication status: Published
• Journal: JOURNAL OF BIOLOGICAL CHEMISTRY
• Volume: 286
• Issue: 35
• Pages: 30606-30614
• Publication date: 2011-09-02
• DOI: 10.1074/jbc.M111.243865
• EISSN: 1083-351X
• ISSN: 0021-9258
• Language: English