Structural basis for GPR40 allosteric agonism and incretin stimulation

Area of Science:

• Structural Biology
• Pharmacology
• Biochemistry

Background:

• Free fatty acid receptor 1 (GPR40) plays a crucial role in metabolic regulation.
• Synthetic agonists activate GPR40 via distinct allosteric sites, influencing receptor function differently.
• Previous studies identified an allosteric site for partial agonists like TAK-875.

Purpose of the Study:

• To determine the crystal structure of human GPR40 bound to a synthetic full agonist.
• To elucidate the binding mode and mechanism of action of a novel GPR40 full agonist.
• To investigate the potential of this site for endogenous free fatty acid (FFA) binding.

Main Methods:

• X-ray crystallography to determine the 2.76-Å crystal structure of human GPR40 complexed with compound 1.
• Biochemical assays to characterize the G protein coupling (Gα_q and Gα_s) of compound 1.
• Computational modeling to assess the binding of endogenous FFA, γ-linolenic acid.

Main Results:

• The crystal structure revealed compound 1 binding to a second, distinct allosteric site near intracellular loop 2 (ICL2).
• Compound 1 functions as a dual Gα_q and Gα_s-coupled full agonist, unlike the Gα_q-specific partial agonist TAK-875.
• Ligand binding stabilizes ICL2, likely enhancing G protein activation; γ-linolenic acid and compound 1 show positive cooperativity with TAK-875.

Conclusions:

• A second allosteric site on GPR40 accommodates full agonists, leading to distinct G protein coupling profiles.
• Stabilization of ICL2 by ligands is a key mechanism for modulating G protein activity at GPR40.
• The identified allosteric site may also serve as a binding pocket for endogenous free fatty acids.