The accessory protein MRAP2 directly interacts with melanocortin-3 receptor to enhance signaling

Area of Science:

• Endocrinology
• Neuroscience
• Molecular Biology

Background:

• The central melanocortin system regulates energy balance.
• Melanocortin-4 receptor (MC4R) and melanocortin-2 receptor accessory protein 2 (MRAP2) are key players, with mutations linked to obesity.
• MC3R, structurally similar to MC4R, influences sexual maturation, growth, and lean mass.

Purpose of the Study:

• To investigate the interaction and functional effect of MRAP2 on MC3R activity.
• To determine if MRAP2 modulates MC3R signaling pathways.
• To assess the impact of obesity-associated MRAP2 variants on MC3R function.

Main Methods:

• Single-molecule pull-down assays and fluorescence photobleaching to study MC3R-MRAP2 interaction and stoichiometry.
• Analysis of coexpression of MRAP2 and MC3R in human brain transcriptomic data.
• HEK293 cell-based assays to measure cAMP signaling, beta-arrestin recruitment, and receptor internalization.
• Alanine mutagenesis and structural homology modeling to identify key interaction residues.
• Functional assessment of obesity-associated MRAP2 variants.

Main Results:

• MC3R and MRAP2 interact and form heterodimers with 1:1 stoichiometry.
• MRAP2 and MC3R are coexpressed in hypothalamic neurons involved in appetite control.
• MRAP2 enhances MC3R-mediated cAMP signaling, reduces beta-arrestin recruitment, and impairs MC3R internalization.
• Specific transmembrane residues are critical for MRAP2-MC3R interaction and MRAP2's modulatory effects.
• Obesity-associated MRAP2 variants failed to enhance MC3R signaling.

Conclusions:

• MRAP2 is an important regulator of MC3R function.
• MRAP2's modulation of MC3R signaling is critical for energy homeostasis.
• Dysfunctional MRAP2 variants contribute to obesity by impairing MC3R signaling.