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

نویسندگان

  • Melanie A McDowell
  • Julien Marcoux
  • Gareth McVicker
  • Steven Johnson
  • Yu Hang Fong
  • Rebecca Stevens
  • Lesley A H Bowman
  • Matteo T Degiacomi
  • Jun Yan
  • Adam Wise
  • Miriam E Friede
  • Justin L P Benesch
  • Janet E Deane
  • Christoph M Tang
  • Carol V Robinson
  • Susan M Lea
چکیده

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.

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عنوان ژورنال:
  • Molecular microbiology

دوره 99 4  شماره 

صفحات  -

تاریخ انتشار 2016