A new system that creates functional maps for the G protein-coupled receptor (GPCR) superfamily could lead to new treatments for conditions as diverse as heart disease and asthma with fewer side effects.
GPCR MAPS (multiplexed assays with pathway specificity) could result in the identification of new druggable sites for these important cell-surface receptors, which form the target of a third of current clinical therapeutics.
The high-throughput method, outlined in Nature Structural & Molecular Biology, offers a speedy and generalizable way to build complete, high-resolution, functional and allosteric maps for this family of 800 proteins.
“We believe that the application of GPCR-MAPS across the GPCR superfamily will advance our understanding of the largest family of human membrane receptors and enable rational, precision drug design,” reported Taylor Mighell, PhD, and Ben Lehner PhD, from the Center for Genomic Regulation in Barcelona, Spain.
GPCRs are the largest family of transmembrane proteins that transmit signals into cells, such as neurotransmitters, metabolites, immune system molecules, pH, and photons of light.
The vast majority of GPCR drugs bind orthosteric sites, attaching to the active site where the natural ligand binds. But structural conservation of these sites makes it difficult to target one receptor without engaging other family members, often causing toxicity and other side effects.
However, there are alternatives to binding at these sites, including biased agonism—also called functional selectivity—and allosteric modulation.
Allosteric drugs targeting nonconserved sites and have the potential advantages of high specificity and reduced toxicity. Furthermore, as allosteric drugs modulate responses to physiological ligands, their effects temporally and spatially match physiological signaling processes.
To investigate further, Mighell and Lehner created GPCR-MAPS to rapidly generate comprehensive functional maps of the family of proteins through a series of four steps.
Firstly, the team generated a complete site-saturation library for a receptor, consisting of all possible amino acid substitutions in all positions. Secondly, they quantified the cell surface expression of the library of variants to quantify defects in fold stability and trafficking.
The researchers then pooled experiments to quantify the recruitment of conformation-specific interaction partners to every receptor variant in response to ligand treatment.
Finally, they integrated the resulting data to generate rich, multimodal, functional maps of how the quantitative and multimodal functions of a receptor were altered by chemically diverse perturbations throughout its entire structure.
The team tested their method on the β2 adrenergic receptor (β2AR), an extensively characterized receptors that is expressed in the cardiovascular system where modulates smooth muscle relaxation and bronchodilation.
Many β2AR agonists are used for treating asthma and chronic obstructive pulmonary disease.
When applied to β2AR, GPCR-MAPS quantified the activation functions and multimodal characteristics of more than 7500 different receptor variants.
The resulting maps revealed a modular receptor architecture, with a core activation network surrounded by residues tuning quantitative parameters and bias. They also identified multiple allosteric surface pockets.
“GPCR drug discovery has proceeded from an era of blind high-throughput screening to an era of structure-based drug discovery,” the authors noted.
“We believe that we are now entering a third era of GPCR drug discovery, where high-resolution functional maps of quantitative signaling parameters empower the rational design of advanced GPCR therapeutics, including precision biased and allosteric modulators.”
