The locus of enterocyte effacement (LEE) is essential for virulence of enterohaemorrhagic Escherichia coli (EHEC) and enteropathogenic E. coli (EPEC). The 41 genes of the LEE encode type III secretion system proteins and three associated regulators: Ler, GrlA and GrlR. Ler is a positive regulator for most of the LEE operons, including grlRA. GrlA controls the expression of ler, ehxCABD and flhDC operons. GrlR binds to GrlA and suppresses its function. Here we report the crystal structure of GrlR-GrlAΔ (aa 1-106) complex (2:1) and its functional characterization. We show that GrlR interacts with the Helix-Turn-Helix motif of GrlA. Moreover, GrlA binds to the promoter DNA fragments of ler, ehxCABD and flhDC, and GrlR outcompetes with these promoter DNA sequences for the Helix-Turn-Helix motif of GrlA. These findings provide mechanistic insight into a regulatory module for the virulence of EPEC and EHEC, two important pathogens that cause devastating diseases.
Bibliographical noteFunding Information:
This work was partially supported by a BMRC grant (WBS R154000461305) from the Agency for Science Technology and Research (A*STAR), Singapore. We acknowledge the National Synchrotron Radiation Research Centre beamline 13B1 of the Taiwan synchrotron facility. I.R. was supported by a grant from the Israeli Science Foundation (ISF). K.Y.L. was supported by a grant from the Natural Science and Engineering Research Council (NSERC) Discovery Grant (372373-2010), Canada and Open Funding Project of the State Key Laboratory of Bioreactor Engineering of China. We acknowledge the assistance provided by Dr Gal Yerushalmi in plasmid construction. A.P. is a graduate scholar in receipt of a research scholarship from the National University of Singapore (NUS).