Common activation mechanism of class A GPCRs

Abstract

Class A G-protein-coupled receptors (GPCRs) influence virtually every aspect of human physiology. Understanding receptor activation mechanism is critical for discovering novel therapeutics since about one-third of all marketed drugs target members of this family. GPCR activation is an allosteric process that couples agonist binding to G-protein recruitment, with the hallmark outward movement of transmembrane helix 6 (TM6). However, what leads to TM6 movement and the key residue level changes of this movement remain less well understood. Here, we report a framework to quantify conformational changes. By analyzing the conformational changes in 234 structures from 45 class A GPCRs, we discovered a common GPCR activation pathway comprising of 34 residue pairs and 35 residues. The pathway unifies previous findings into a common activation mechanism and strings together the scattered key motifs such as CWxP, DRY, Na+ pocket, NPxxY and PIF, thereby directly linking the bottom of ligand-binding pocket with G-protein coupling region. Site-directed mutagenesis experiments support this proposition and reveal that rational mutations of residues in this pathway can be used to obtain receptors that are constitutively active or inactive. The common activation pathway provides the mechanistic interpretation of constitutively activating, inactivating and disease mutations. As a module responsible for activation, the common pathway allows for decoupling of the evolution of the ligand binding site and G-protein-binding region. Such an architecture might have facilitated GPCRs to emerge as a highly successful family of proteins for signal transduction in nature.

Enigmatic Histamine Receptor H4 for Potential Treatment of Multiple Inflammatory, Autoimmune, and Related Diseases

“…Being a member of the most populated class A of the GPCR superfamily, human H 4 R also contains seven transmembrane helices and a short amphipathic helix that possibly runs parallel to the cytosolic membrane surface. It consists of 390 amino acid residues possessing all of the highly conserved sequence motifs [16,17] of the class A GPCRs including the most evolutionary conserved residues in each of the transmembrane helices: N1.50, D2.50, R3.50, W4.50, P5.50, P6.50, and P7.50 (Ballesteros-Weinstein numbering [18]) indicating the same activation mechanism of H 4 R as that of the other receptors in class A GPCRs [19]. The Ballesteros-Weinstein numbering scheme of GPCRs provides information about the relative positions of amino acids present in seven transmembrane helices.…”

Ion-water coupling controls class A GPCR signal transduction pathways

“…Since transmembrane signal transduction is a process of information transfer, we developed a new methodology based on the principles of Shannon's information theory and coinformation (19,21). Our methodology, termed "State Specific Information" (SSI), traces information pathways through coupled transitions in residue and cofactor conformational state changes, such as those between active and inactive receptor microswitches, which are caused by receiving a signal on one side of the GPCR (15,16). SSI is however not limited to GPCRs.…”

“…Various studies have correlated GPCR activation with transitions between distinct rotameric conformations of evolutionarily conserved residues termed microswitches. These rotamer transitions are thought to underpin the large scale conformational changes that govern activation (1,7,(9)(10)(11)(12)(13)(14)(15)(16). Many microswitches form distinct motifs, such as the CWxP motif at the ligand binding site, which is known to link directly to the sodium ion binding pocket (5).…”

Capturing Peptide–GPCR Interactions and Their Dynamics

“…These studies have greatly increased our structural and functional understanding of these receptors [ 29 , 30 , 31 , 32 ], and also identified some common structural hallmarks in each receptor family. For instance, there is a short β-hairpin located in the second extracellular loop (ECL2) of rhodopsin-like peptide GPCRs [ 29 ], which facilitates access to the transmembrane binding cavity.…”