A Single Amino Acid Determines Lysophospholipid Specificity of the S1P 1 (EDG1) and LPA1 (EDG2) Phospholipid Growth Factor Receptors


The phospholipid growth factors sphingosine-1-phosphate (S1P) and lysophosphatidic acid (LPA) are ligands for the related G protein-coupled receptors S1P1/EDG1 and LPA1/EDG2, respectively. We have developed a model of LPA1 that predicts interactions between three polar residues and LPA. One of these, glutamine 125, which is conserved in the LPA receptor subfamily (LPA1/EDG2, LPA2/EDG4, and LPA 3/EDG7), hydrogen bonds with the LPA hydroxyl group. Our previous S1P1 study identified that the corresponding glutamate residue, conserved in all S1P receptors, ion pairs with the S1P ammonium. These two results predict that this residue might influence ligand recognition and specificity. Characterization of glutamate/glutamine interchange point mutants of S1P1 and LPA1 validated this prediction as the presence of glutamate was required for S1P recognition, whereas LPA recognition was possible with either glutamine or glutamate. The most likely explanation for this dual specificity behavior is a shift in the equilibrium between the acid and conjugate base forms of glutamic acid due to other amino acids surrounding that position in LPA1, producing a mixture of receptors including those having an anionic glutamate that recognize S1P and others with a neutral glutamic acid that recognize LPA. Thus, computational modeling of these receptors provided valid information necessary for understanding the molecular pharmacology of these receptors.

Publication Title

Journal of Biological Chemistry