RO4988546

BACKGROUND AND PURPOSEAltered glutamatergic neurotransmission is linked to several neurological and psychiatric disorders. Metabotropic glutamate receptor 2 (mGlu2) plays an important role on the presynaptic control of glutamate release and negative allosteric modulators (NAMs) acting on mGlu2/3receptors are under assessment for their potential as antidepressants, neurogenics and cognitive enhancers. Two new potent mGlu2/3NAMs, RO4988546 and RO5488608, are described in this study and the allosteric binding site in the transmembrane (TM) domain of mGlu2is characterized.EXPERIMENTAL APPROACHSite directed mutagenesis, functional measurements and β2‐adrenoceptor‐based modelling of mGlu2were employed to identify important molecular determinants of two new potent mGlu2/3NAMs.KEY RESULTSRO4988546 and RO5488608 affected both [3H]‐LY354740 agonist binding at the orthosteric site and the binding of a tritiated positive allosteric modulator (3H‐PAM), indicating that NAMs and PAMs could have overlapping binding sites in the mGlu2TM domain. We identified eight residues in the allosteric binding pocket that are crucial for non‐competitive antagonism of agonist‐dependent activation of mGlu2and directly interact with the NAMs: Arg3.28, Arg3.29, Phe3.36, HisE2.52, Leu5.43, Trp6.48, Phe6.55and Val7.43. The mGlu2specific residue HisE2.52is likely to be involved in selectivity and residues located in the outer part of the binding pocket are more important for [3H]‐LY354740 agonist binding inhibition, which is independent of the highly conserved Trp6.48residue.CONCLUSIONS AND IMPLICATIONSThis is the first complete molecular investigation of the allosteric binding pocket of mGlu2and Group II mGluRs and provides new information on what determines mGlu2NAMs selective interactions and effects.