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Characterisation of Shigella Spa33 and Thermotoga FliM/N reveals a new model for C-ring assembly in T3SS

DOI: 10.1111/mmi.13267 DOI Help
PMID: 26538516 PMID Help

Authors: Melanie A Mcdowell (University of Oxford) , Julien Marcoux (University of Oxford) , Gareth Mcvicker (University of Oxford) , Steven Johnson (University of Oxford) , Yu Hang Fong (University of Oxford) , Rebecca Stevens (University of Oxford) , Lesley A. Bowman (University of Oxford) , Matteo T. Degiacomi (University of Oxford) , Jun Yan (University of Oxford) , Adam Wise (University of Oxford) , Miriam Friede (University of Oxford) , Justin L. P. Benesch (University of Oxford) , Janet E. Deane (University of Oxford) , Christoph M. Tang (University of Oxford) , Carol V. Robinson (University of Oxford) , Susan M. Lea (University of Oxford)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Molecular Microbiology

State: Published (Approved)
Published: November 2015
Diamond Proposal Number(s): 9306

Open Access Open Access

Abstract: Flagellar Type III secretion systems (T3SS) contain an essential Cytoplasmic-ring (C-ring) largely composed of two proteins FliM and FliN, whilst an analogous substructure for the closely related non-flagellar (NF) T3SS has not been observed in situ. We show that the spa33 gene encoding the putative NF-T3SS C-ring component in Shigella flexneri is alternatively translated to produce both full-length (Spa33-FL) and a short variant (Spa33-C), with both required for secretion. They associate in a 1:2 complex (Spa33-FL/C2) that further oligomerises into elongated arrays in vitro. The structure of Spa33-C2 and identification of an unexpected intramolecular pseudodimer in Spa33-FL, reveals a molecular model for their higher order assembly within NF-T3SS. Spa33-FL and Spa33-C are identified as functional counterparts of a FliM-FliN fusion and free FliN respectively. Furthermore, we show that Thermotoga maritima FliM and FliN form a 1:3 complex structurally equivalent to Spa33-FL/C2, allowing us to propose a unified model for C-ring assembly by NF-T3SS and flagellar-T3SS.

Subject Areas: Biology and Bio-materials

Instruments: I04-Macromolecular Crystallography

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