7AWA

SctV (SsaV) cytoplasmic domain

Summary for 7AWA

• Entry DOI: 10.2210/pdb7awa/pdb
• EMDB information: 11928
• Descriptor: Secretion system apparatus protein SsaV (1 entity in total)
• Functional Keywords: type iii secretion, t3ss, export apparatus, protein transport
• Biological source: Salmonella typhimurium (strain LT2 / SGSC1412 / ATCC 700720)
• Total number of polymer chains: 1
• Total formula weight: 76221.36

Authors

Matthews-Palmer, T.R.S.,Gonzalez-Rodriguez, N.,Calcraft, T.,Lagercrantz, S.,Zachs, T.,Yu, X.J.,Grabe, G.,Holden, D.,Nans, A.,Rosenthal, P.,Rouse, S.,Beeby, M. (deposition date: 2020-11-06, release date: 2021-04-14, Last modification date: 2024-05-01)

Primary citation

Matthews-Palmer, T.R.S.,Gonzalez-Rodriguez, N.,Calcraft, T.,Lagercrantz, S.,Zachs, T.,Yu, X.J.,Grabe, G.J.,Holden, D.W.,Nans, A.,Rosenthal, P.B.,Rouse, S.L.,Beeby, M.
Structure of the cytoplasmic domain of SctV (SsaV) from the Salmonella SPI-2 injectisome and implications for a pH sensing mechanism.
J.Struct.Biol., 213:107729-107729, 2021

PubMed Abstract: Bacterial type III secretion systems assemble the axial structures of both injectisomes and flagella. Injectisome type III secretion systems subsequently secrete effector proteins through their hollow needle into a host, requiring co-ordination. In the Salmonella enterica serovar Typhimurium SPI-2 injectisome, this switch is triggered by sensing the neutral pH of the host cytoplasm. Central to specificity switching is a nonameric SctV protein with an N-terminal transmembrane domain and a toroidal C-terminal cytoplasmic domain. A 'gatekeeper' complex interacts with the SctV cytoplasmic domain in a pH dependent manner, facilitating translocon secretion while repressing effector secretion through a poorly understood mechanism. To better understand the role of SctV in SPI-2 translocon-effector specificity switching, we purified full-length SctV and determined its toroidal cytoplasmic region's structure using cryo-EM. Structural comparisons and molecular dynamics simulations revealed that the cytoplasmic torus is stabilized by its core subdomain 3, about which subdomains 2 and 4 hinge, varying the flexible outside cleft implicated in gatekeeper and substrate binding. In light of patterns of surface conservation, deprotonation, and structural motion, the location of previously identified critical residues suggest that gatekeeper binds a cleft buried between neighboring subdomain 4s. Simulations suggest that a local pH change from 5 to 7.2 stabilizes the subdomain 3 hinge and narrows the central aperture of the nonameric torus. Our results are consistent with a model of local pH sensing at SctV, where pH-dependent dynamics of SctV cytoplasmic domain affect binding of gatekeeper complex.

PubMed: 33774138
DOI: 10.1016/j.jsb.2021.107729

Experimental method

ELECTRON MICROSCOPY (3.5 Å)