Family B G Protein-coupled Receptors and their Ligands: From Structure to Function

Background: Family B G protein-coupled receptors (GPCRs) play an important role in many physiological and pathophysiological processes. They are plasma-membrane proteins containing an extracellular N-domain, an intracellular C-tail, seven transmembrane domains (TMs), three extracellular (ELs) and three intracellular (ILs) loops. Objective: This review aims to summarize the current structural and functional information for family B GPCRs and their ligands, as well as, their physiological and pathophysiological role. Methods: thorough search of bibliographic databases for peer-reviewed research literature was undertaken. Moreover, molecular models of family B GPCRs were constructed and a structural alignment of their amino acid sequences was performed to demonstrate common structural characteristics. Results: In this review the family B GPCRs and their complexes with the receptor activity modifying proteins (RAMPs) were classified into five groups and the important physiological and pathophysiological role of these receptors was summarized. In addition, conserved residues of the Ndomain and the TMs of these receptors were numbered, thus making feasible the comparison of receptor structures and demonstrating common structural characteristics that are functionally important for all family B receptors. Molecular models created in this study were used to discuss the molecular mechanisms underlying ligand binding to family B GPCRs and receptor activation. Conclusion: The findings of this review provide information about the structural-functional determinants of family B GPCRs and their ligands, thus boosting the design of novel drugs with better potencies and bioavailabilities, which might enrich the therapeutic armory for the treatment of a wide spectrum of family B GPCRs-related disorders.