Unique Features of Different Classes of G-Protein-Coupled Receptors Revealed from Sequence Coevolutionary and Structural Analysis
G-protein-coupled receptors (GPCRs) are the largest family of human membrane proteins and serve as the primary targets of about one third of currently marketed drugs. Despite the critical importance, experimental structures have been determined for only a limited portion of GPCRs. Functional mechanisms of GPCRs remain poorly understood. Here, we have constructed sequence coevolutionary models of the A, B and C classes of GPCRs and compared them with residue contact frequency maps generated with
... available experimental structures. Significant portions of structural residue contacts have been successfully detected in the sequence-based covariational models. "Exception" residue contacts predicted from sequence coevolutionary models but not available structures added missing links that were important for GPCR activation and allosteric modulation. Our combined coevolutionary and structural analysis revealed unique features of the different classes of GPCRs. First, we provided evidence from coevolutionary couplings that dimerization is required for activation of class C GPCRs, but not for activation of class A and B GPCRs. Second, we identified distinct residue contacts involving different sets of functional motifs for activation of the class A and B GPCRs. Finally, we uncovered critical residue contacts tuned by allosteric modulation in the three classes of GPCRs. These findings provide a promising framework for designing selective therapeutics of GPCRs.