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Molecular Organization of Soluble Type III Secretion System Sorting Platform Complexes.

Bernal, Ivonne
; 
Börnicke, Jonathan
; 
Heidemann, Johannes
; 
Svergun, Dmitri
; 
Horstmann, Julia A
; ; 
Tuukkanen, Anne
; 
Uetrecht, Charlotte
; 
Kolbe, Michael
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Issue Date
2019-07-06
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Abstract
Many medically relevant Gram-negative bacteria use the type III secretion system (T3SS) to translocate effector proteins into the host for their invasion and intracellular survival. A multi-protein complex located at the cytosolic interface of the T3SS is proposed to act as a sorting platform by selecting and targeting substrates for secretion through the system. However, the precise stoichiometry and 3D organization of the sorting platform components are unknown. Here we reconstitute soluble complexes of the Salmonella Typhimurium sorting platform proteins including the ATPase InvC, the regulator OrgB, the protein SpaO and a recently identified subunit SpaOC, which we show to be essential for the solubility of SpaO. We establish domain-domain interactions, determine for the first time the stoichiometry of each subunit within the complexes by native mass spectrometry and gain insight into their organization using small-angle X-ray scattering. Importantly, we find that in solution the assembly of SpaO/SpaOC/OrgB/InvC adopts an extended L-shaped conformation resembling the sorting platform pods seen in in situ cryo-electron tomography, proposing that this complex is the core building block that can be conceivably assembled into higher oligomers to form the T3SS sorting platform. The determined molecular arrangements of the soluble complexes of the sorting platform provide important insights into its architecture and assembly.
Citation
J Mol Biol. 2019 Jul 6. pii: S0022-2836(19)30425-5. doi: 10.1016/j.jmb.2019.07.004.
Affiliation
CSSB, Centre for Structural Systembiologie, Notkestr.85, 22607 Hamburg. Germany.
Publisher
Elsevier
Journal
Journal of Molecular Biology
URI
http://hdl.handle.net/10033/621919
DOI
10.1016/j.jmb.2019.07.004
PubMed ID
31288030
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Article
Language
en
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ISSN
1089-8638
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Attribution-NonCommercial-ShareAlike 4.0 International
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publications of the research group structural infection biology ([CSSB] STIB)