GrlR is a family of protobacterial type III secretion system negative regulators. Structurally, GrlR consists of a typical beta-barrel fold with eight beta-strands containing an internal hydrophobic cavity and a plug-like loop on one side of the barrel. Strong hydrophobic interactions between the two beta-barrels maintain its dimeric architecture. A unique surface-exposed EDED (Glu-Asp-Glu-Asp) motif is identified to be critical for GrlA-GrlR interaction and for the repressive activity of GrlR [1]. The locus of enterocyte effacement (LEE) is essential for virulence of enterohaemorrhagic Escherichia coli (EHEC) and enteropathogenic E. coli (EPEC). It encodes some 20 genes including an overall regulator ler and two others, GrlR and GrlA, that form the type three secretion system for infection. GrlR comlexes with GrlA to repress expression of ler [2]. GrlA is found in family Pfam:PF00462.

1: Structure of GrlR and the implication of its EDED motif in mediating the regulation of type III secretion system in EHEC. Jobichen C, Li M, Yerushalmi G, Tan YW, Mok YK, Rosenshine I, Leung KY, Sivaraman J; PLoS Pathog. 2007;3:e69. PMID:17511515

2: Structure of GrlR-GrlA complex that prevents GrlA activation of virulence genes. Padavannil A, Jobichen C, Mills E, Velazquez-Campoy A, Li M, Leung KY, Mok YK, Rosenshine I, Sivaraman J; Nat Commun. 2013;4:2546. PMID:24092262