Structural determinants of allosteric antagonism at metabotropic glutamate receptor 2: mechanistic studies with new potent negative allosteric modulators

Br J Pharmacol. 2011 Sep;164(2b):521-37. doi: 10.1111/j.1476-5381.2011.01409.x.

Abstract

Background and purpose: Altered 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 mGlu₂/₃ receptors are under assessment for their potential as antidepressants, neurogenics and cognitive enhancers. Two new potent mGlu₂/₃ NAMs, RO4988546 and RO5488608, are described in this study and the allosteric binding site in the transmembrane (TM) domain of mGlu₂ is characterized.

Experimental approach: Site directed mutagenesis, functional measurements and β₂-adrenoceptor-based modelling of mGlu₂ were employed to identify important molecular determinants of two new potent mGlu₂/₃ NAMs.

Key results: RO4988546 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 mGlu₂ TM domain. We identified eight residues in the allosteric binding pocket that are crucial for non-competitive antagonism of agonist-dependent activation of mGlu₂ and directly interact with the NAMs: Arg³·²⁸, Arg³·²⁹, Phe³·³⁶, His(E2.52) , Leu⁵·⁴³, Trp⁶·⁴⁸, Phe⁶·⁵⁵ and Val⁷·⁴³. The mGlu₂ specific residue His(E2.52) is 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 Trp⁶·⁴⁸ residue.

Conclusions and implications: This is the first complete molecular investigation of the allosteric binding pocket of mGlu₂ and Group II mGluRs and provides new information on what determines mGlu₂ NAMs selective interactions and effects.

MeSH terms

  • Allosteric Regulation
  • Allosteric Site
  • Amino Acid Sequence
  • Animals
  • Binding Sites
  • Bridged Bicyclo Compounds / chemistry
  • Bridged Bicyclo Compounds / pharmacology
  • CHO Cells
  • Calcium / metabolism
  • Cells, Cultured
  • Cricetinae
  • HEK293 Cells
  • Humans
  • Models, Molecular
  • Molecular Sequence Data
  • Protein Binding / drug effects
  • Protein Structure, Tertiary
  • Rats
  • Receptors, Metabotropic Glutamate / antagonists & inhibitors*
  • Receptors, Metabotropic Glutamate / chemistry*
  • Receptors, Metabotropic Glutamate / genetics
  • Receptors, Metabotropic Glutamate / metabolism
  • Sequence Alignment / methods
  • Structure-Activity Relationship

Substances

  • Bridged Bicyclo Compounds
  • Receptors, Metabotropic Glutamate
  • metabotropic glutamate receptor 2
  • eglumetad
  • Calcium