Molecular recognition in purinergic receptors. 1. A comprehensive computational study of the h-P2Y₁-receptor

P2Y receptors (P2Y-Rs) are attractive pharmaceutical targets due to their involvement in the modulation of many tissues and organs. The lack of experimental structural data on P2Y-Rs impedes structure-based drug design. The need to elucidate the receptor's molecular recognition, together with the limitations of previous receptor models, triggered the construction of a new molecular model for the h-P2Y₁-R. Therefore, a h-P2Y₁-R model was constructed by homology modeling using the 2.6 Å crystal structure of bovine rhodopsin as a template and subsequently refined by constrained molecular dynamics (MD) simulations in a fully hydrated lipid bilayer environment. ATP was docked into the receptor binding site, followed by binding site refinement using Monte Carlo and MD simulations. Analysis of the h-P2Y₁-R-ATP complex suggests that the triphosphate moiety is tightly bound by a multitude of interactions possibly including a Mg²⁺ ion, the ribose ring is not involved in specific interactions, and the adenine ring is bound via N1, N7, and N⁶. The molecular recognition of the h-P2Y₁-R was further probed by ATP derivatives modified on the adenine ring, and correlated with EC₅₀ values for these derivatives. Analysis of recepton:ligand complexes and quantum mechanical studies on model compounds support the role of both steric and electronic effects in improving H-bonding (via N1 and N⁶) and π-stacking interactions. The computed h-P2Y₁-R model was validated with respect to our previous biochemical results. We believe that this new model of the h-P2Y₁-R provides the means for understanding phenomena such as the ligand's potency and receptor subtype selectivity.