Stabilization of F-actin by Salmonella effector SipA resembles the structural effects of inorganic phosphate and phalloidin

Entry of into host enterocytes strictly relies on its pathogenicity island 1 effector SipA. We found that SipA binds to F-actin in a unique mode in a 1:2 stoichiometry with picomolar affinity. A cryo-EM reconstruction revealed that SipA's globular core binds at the grove between actin strands,...

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Bibliographic Details
Published inbioRxiv
Main Authors Niedzialkowska, Ewa, Runyan, Lucas A, Kudryashova, Elena, Egelman, Edward H, Kudryashov, Dmitri S
Format Journal Article Paper
LanguageEnglish
Published United States Cold Spring Harbor Laboratory Press 26.12.2023
Subjects
Actin
Cofilin
Cytoskeleton
Depolymerization
Enterocytes
Mechanical properties
Pathogenicity
Phalloidin
Salmonella
Stoichiometry
SipA
actin
cryo-EM
actin-specific toxins
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Summary:Entry of into host enterocytes strictly relies on its pathogenicity island 1 effector SipA. We found that SipA binds to F-actin in a unique mode in a 1:2 stoichiometry with picomolar affinity. A cryo-EM reconstruction revealed that SipA's globular core binds at the grove between actin strands, whereas the extended C-terminal arm penetrates deeply into the inter-strand space, stabilizing F-actin from within. The unusually strong binding of SipA is achieved via a combination of fast association via the core and very slow dissociation dictated by the arm. Similarly to P , BeF , and phalloidin, SipA potently inhibited actin depolymerization by ADF/cofilin, which correlated with the increased filament stiffness, supporting the hypothesis that F-actin's mechanical properties contribute to the recognition of its nucleotide state by protein partners. The remarkably strong binding to F-actin maximizes the toxin's effects at the injection site while minimizing global influence on the cytoskeleton and preventing pathogen detection by the host cell.
DOI:10.1101/2023.12.26.573373