Identification and characterization of the lipid-binding property of GrIR, a locus of enterocyte effacement regulator

Lipocalins are it broad family of proteins identified initially in eukaryotes and more recently in Gram-negative bacteria. The functions of lipocalin or lipid-binding proteins are often elusive and very diverse. Recently, we have determined the structure of GrIR (global regulator of LEE repressor), which plays a key role in the regulation of LEE (locus of enterocyte effacement) proteins. GrIR adopts a lipocalin-like fold that is composed of an eight-stranded beta-barrel followed byan alpha-helix at the C-terminus. GrIR has it highly hydrophobic cavity region and could be a potential transporter of lipophilic molecules. To verily this hypothesis, we carried out structure-bused analysis of GrIR, determined the structure of the lipid-GrIR complex told measured the binding of lipid to recombinant GrIR by ITC (isothermal titration calorimetry). In addition. we identified phosphatidylglycerol and phosphatidylethanolamine its the endogenously bound lipid species of GrIR using electrosprity-ionization MS. Furthermore, we have shown that the lipid-binding property of GrIR is similar to that of its closet lipocalin structural homologus, beta-lactoglobulin. Our studies demonstrate the hitherto unknown lipid-binding property of GrIR.