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PLoS Pathog. 2019 Jan 22;15(1):e1007565. doi: 10.1371/journal.ppat.1007565. eCollection 2019 Jan.

Role of SpaO in the assembly of the sorting platform of a Salmonella type III secretion system.

Author information

1
Department of Microbial Pathogenesis Yale University School of Medicine, New haven, CT, United States of America.
2
Microbial Science Institute, Yale University School of Medicine, New haven, CT, United States of America.
3
Department of Microbiology and Molecular Genetics McGovern Medical School, The University of Texas Health Science Center at Houston, TX, United States of America.
4
Pathology and Laboratory Medicine, McGovern Medical School, The University of Texas Health Science Center at Houston, TX, United States of America.

Abstract

Many bacterial pathogens and symbionts use type III secretion machines to interact with their hosts by injecting bacterial effector proteins into host target cells. A central component of this complex machine is the cytoplasmic sorting platform, which orchestrates the engagement and preparation of type III secreted proteins for their delivery to the needle complex, the substructure of the type III secretion system that mediates their passage through the bacterial envelope. The sorting platform is thought to be a dynamic structure whose components alternate between assembled and disassembled states. However, how this dynamic behavior is controlled is not understood. In S. Typhimurium a core component of the sorting platform is SpaO, which is synthesized in two tandemly translated products, a full length (SpaOL) and a short form (SpaOS) composed of the C-terminal 101 amino acids. Here we show that in the absence of SpaOS the assembly of the needle substructure of the needle complex, which requires a functional sorting platform, can still occur although with reduced efficiency. Consistent with this observation, in the absence of SpaOS secretion of effectors proteins, which requires a fully assembled injectisome, is only slightly compromised. In the absence of SpaOS we detect a significant number of fully assembled needle complexes that are not associated with fully assembled sorting platforms. We also find that although binding of SpaOL to SpaOS can be detected in the absence of other components of the sorting platform, this interaction is not detected in the context of a fully assembled sorting platform suggesting that SpaOS may not be a core structural component of the sorting platform. Consistent with this observation we find that SpaOS and OrgB, a component of the sorting platform, share the same binding surface on SpaOL. We conclude that SpaOS regulates the assembly of the sorting platform during type III secretion.

PMID:
30668610
PMCID:
PMC6358110
DOI:
10.1371/journal.ppat.1007565
[Indexed for MEDLINE]
Free PMC Article

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