Mapping the Binding Sites of UDP and Prostaglandin E2 Glyceryl Ester in the Nucleotide Receptor P2Y6

Abstract

Cyclooxygenase-2 catalyzes the biosynthesis of prostaglandins from arachidonic acid and the biosynthesis of prostaglandin glycerol esters (PG-Gs) from 2-arachidonoylglycerol. PG-Gs are mediators of several biological actions such as macrophage activation, hyperalgesia, synaptic plasticity, and intraocular pressure. Recently, the human UDP receptor P2Y₆ was identified as a target for the prostaglandin E2 glycerol ester (PGE₂ -G). Here, we show that UDP and PGE₂ -G are evolutionary conserved endogenous agonists at vertebrate P2Y₆ orthologs. Using sequence comparison of P2Y₆ orthologs, homology modeling, and ligand docking studies, we proposed several receptor positions participating in agonist binding. Site-directed mutagenesis and functional analysis of these P2Y₆ mutants revealed that both UDP and PGE₂ -G share in parts one ligand-binding site. Thus, the convergent signaling of these two chemically very different agonists has already been manifested in the evolutionary design of the ligand-binding pocket.

Keywords: G protein-coupled receptors; PGE2-G; UDP; binding site; site-directed mutagenesis.