Cookies on this website
We use cookies to ensure that we give you the best experience on our website. If you click 'Continue' we'll assume that you are happy to receive all cookies and you won't see this message again. Click 'Find out more' for information on how to change your cookie settings.

Flagellar type III secretion systems (T3SS) contain an essential cytoplasmic-ring (C-ring) largely composed of two proteins FliM and FliN, whereas 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 reveal 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.

Original publication

DOI

10.1111/mmi.13267

Type

Journal article

Journal

Mol Microbiol

Publication Date

02/2016

Volume

99

Pages

749 - 766

Keywords

Amino Acid Sequence, Bacterial Proteins, Crystallization, Crystallography, X-Ray, Flagella, Mass Spectrometry, Models, Molecular, Protein Conformation, Protein Multimerization, Shigella flexneri, Thermotoga maritima, Type III Secretion Systems