Open AccessNovel insights into the mechanism of SepL‐mediated control of effector secretion in enteropathogenic Escherichia coli
Author(s) -
Gaytán Meztlli O.,
Monjarás Feria Julia,
Soto Eduardo,
Espinosa Norma,
Benítez Julia M.,
Georgellis Dimitris,
GonzálezPedrajo Bertha
Publication year - 2018
Publication title -
microbiologyopen
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.881
H-Index - 36
ISSN - 2045-8827
DOI - 10.1002/mbo3.571
Subject(s) - secretion , effector , chaperone (clinical) , virulence , microbiology and biotechnology , biology , translocon , type three secretion system , enteropathogenic escherichia coli , calcium , escherichia coli , biochemistry , chromosomal translocation , chemistry , gene , medicine , organic chemistry , pathology
Abstract Type three secretion systems (T3 SS s) are virulence determinants employed by several pathogenic bacteria as molecular syringes to inject effector proteins into host cells. Diarrhea‐producing enteropathogenic Escherichia coli ( EPEC ) uses a T3 SS to colonize the intestinal tract. T3S is a highly coordinated process that ensures hierarchical delivery of three classes of substrates: early (inner rod and needle subunits), middle (translocators), and late (effectors). Translocation of effectors is triggered upon host‐cell contact in response to different environmental cues, such as calcium levels. The T3S substrate specificity switch from middle to late substrates in EPEC is regulated by the SepL and SepD proteins, which interact with each other and form a trimeric complex with the chaperone CesL. In this study, we investigated the link between calcium concentration and secretion regulation by the gatekeeper SepL. We found that calcium depletion promotes late substrate secretion in a translocon‐independent manner. Furthermore, the stability, formation, and subcellular localization of the SepL/SepD/CesL regulatory complex were not affected by the absence of calcium. In addition, we demonstrate that SepL interacts in a calcium‐independent manner with the major export gate component EscV, which in turn interacts with both middle and late secretion substrates, providing a docking site for T3S. These results suggest that EscV serves as a binding platform for both the SepL regulatory protein and secreted substrates during the ordered assembly of the T3 SS .