7FED

Cryo-EM structure of the nonameric SsaV cytosolic domain with D9 symmetry

Summary for 7FED

• Entry DOI: 10.2210/pdb7fed/pdb
• EMDB information: 31553
• Descriptor: Secretion system apparatus protein SsaV (1 entity in total)
• Functional Keywords: transporter, protein transport
• Biological source: Salmonella enterica subsp. enterica serovar Typhimurium str. LT2
• Total number of polymer chains: 18
• Total formula weight: 686235.24

Authors

Xu, J.H.,Zhang, Y.Q.,Gao, X. (deposition date: 2021-07-19, release date: 2022-02-16, Last modification date: 2024-06-12)

Primary citation

Xu, J.,Wang, J.,Liu, A.,Zhang, Y.,Gao, X.
Structural and Functional Analysis of SsaV Cytoplasmic Domain and Variable Linker States in the Context of the InvA-SsaV Chimeric Protein.
Microbiol Spectr, 9:e0125121-e0125121, 2021

PubMed Abstract: The type III secretion (T3S) injectisome is a syringe-like protein-delivery nanomachine widely utilized by Gram-negative bacteria. It can deliver effector proteins directly from bacteria into eukaryotic host cells, which is crucial for the bacterial-host interaction. Intracellular pathogen Salmonella enterica serovar Typhimurium encodes two sets of T3S injectisomes from Salmonella pathogenicity islands 1 and 2 (SPI-1 and SPI-2), which are critical for its host invasion and intracellular survival, respectively. The inner membrane export gate protein, SctV (InvA in SPI-1 and SsaV in SPI-2), is the largest component of the injectisome and is essential for assembly and function of T3SS. Here, we report the 2.11 Å cryo-EM structure of the SsaV cytoplasmic domain (SsaV) in the context of a full-length SctV chimera consisting of the transmembrane region of InvA, the linker of SsaV (SsaV) and SsaV. The structural analysis shows that SsaV exists in a semi-open state and SsaV exhibits two major orientations, implying a highly dynamic process of SsaV for the substrate selection and secretion in a full-length context. A biochemical assay indicates that SsaV plays an essential role in maintaining the nonameric state of SsaV. This study offers near atomic-level insights into how SsaV and SsaV facilitate the assembly and function of SsaV and may lead to the development of potential anti-virulence therapeutics against T3SS-mediated bacterial infection. Type III secretion system (T3SS) is a multicomponent nanomachine and a critical virulence factor for a wide range of Gram-negative bacterial pathogens. It can deliver numbers of effectors into the host cell to facilitate the bacterial host infection. Export gate protein SctV, as one of the engines of T3SS, is at the center of T3SS assembly and function. In this study, we show the high-resolution atomic structure of the cytosolic domain of SctV in the nonameric state with variable linker conformations. Our first observation of conformational changes of the linker region of SctV and the semi-open state of the cytosolic domain of SctV in the full-length context further support that the substrate selection and secretion process of SctV is highly dynamic. These findings have important implications for the development of therapeutic strategies targeting SctV to combat T3SS-mediated bacterial infection.

PubMed: 34851139
DOI: 10.1128/Spectrum.01251-21

Experimental method

ELECTRON MICROSCOPY (3.55 Å)