MCHR2

MCHR2 is a G protein-coupled receptor for melanin-concentrating hormone (MCH) that transduces ligand binding into Gαq-mediated intracellular signaling (PMID:11404457, PMID:11459838). It binds MCH with high affinity (Kd ~0.17–2.2 nM) and, upon activation, drives inositol phosphate turnover and intracellular Ca2+ release while leaving forskolin-stimulated cAMP production unaffected; its signaling is insensitive to pertussis toxin, establishing exclusive Gq coupling and distinguishing it mechanistically from the Gi/Go- and Gq-coupled MCHR1 (PMID:11404457, PMID:11459838). The receptor discriminates ligand orthologs, with salmon MCH showing ~10-fold weaker potency than mammalian MCH at MCHR2 (PMID:11459838), and this Gq-restricted profile is conserved in the rhesus ortholog (PMID:12182940). Receptor abundance directly governs signaling output: shRNA knockdown of MCHR2 proportionally reduces MCH binding, ligand affinity, and MCH-stimulated Ca2+ release (PMID:20937223). Two natural coding variants (R63K, R152Q) do not alter binding or signaling (PMID:15340116). Beyond ligand binding and proximal Gq/PLC/Ca2+ coupling, the physiological and tissue-level roles of MCHR2 have not been characterized in the available corpus.

1. 2001 High

   Established that MCHR2 is a bona fide MCH receptor and defined its G protein coupling, resolving how it differs signally from the previously known MCHR1.

   Evidence Radioligand binding, inositol phosphate turnover, intracellular Ca2+ and cAMP assays with pertussis toxin treatment in mammalian and stable CHO cells, across two independent labs

   PMID:11404457 PMID:11459838

   Open questions at the time

   • Does not define the structural basis of Gq selectivity
   • Endogenous tissue context and physiological output not addressed
   • Ligand ortholog selectivity at MCHR2 only partly mapped
2. 2001 High

   Showed MCHR2 distinguishes MCH orthologs pharmacologically, revealing receptor-specific ligand recognition not seen at MCHR1.

   Evidence Radioligand binding, Ca2+, IP and cAMP assays comparing salmon versus mammalian MCH potency in stable CHO cells

   PMID:11459838

   Open questions at the time

   • Residues governing ortholog discrimination not identified
   • No structural model of the ligand-binding pocket
3. 2002 Medium

   Demonstrated that the Gq-exclusive signaling mode is conserved across primates, supporting it as an intrinsic receptor property rather than a cell-context artifact.

   Evidence Radioligand binding (Kd 2.2 nM) and signaling assays of cloned rhesus MCH-R2 in expressing cells

   PMID:12182940

   Open questions at the time

   • Single-lab characterization
   • No comparison of downstream physiology between species
4. 2004 Medium

   Tested whether common coding variants alter receptor function, addressing a candidate-gene link to phenotypic variation.

   Evidence Site-directed mutagenesis of R63K and R152Q variants with binding, cAMP and Ca2+ assays in CHO cells

   PMID:15340116

   Open questions at the time

   • Variants tested only in a heterologous system
   • No in vivo or expression-level consequences assessed
5. 2009 Medium

   Provided refined quantitative binding and signaling parameters for the human receptor, anchoring affinity and potency values.

   Evidence Radioligand binding (Kd 0.170 nM) and intracellular Ca2+ assay (EC50 2.32 nM) in stable CHO cells

   PMID:20099459

   Open questions at the time

   • Single study, single lab
   • No endogenous-cell measurements
6. 2010 Medium

   Established that receptor protein abundance is rate-limiting for downstream signaling, linking expression level directly to Gq/Ca2+ output magnitude.

   Evidence shRNA knockdown in CHO cells with RT-PCR, western blot, radioligand binding and Ca2+ assays

   PMID:20937223

   Open questions at the time

   • Demonstrated only in an overexpression CHO system
   • Does not address regulation of MCHR2 expression in native tissues

• The physiological roles, native tissue signaling, regulatory inputs, and structural basis of ligand recognition for MCHR2 remain undefined in the available corpus.
• No in vivo functional studies
• No structural data on ligand binding or Gq engagement
• Endogenous expression and downstream physiology uncharacterized