GPCRdb contains data, diagrams and web tools for G protein-coupled receptors (GPCRs). Users can browse all GPCR crystal structures and the largest collections of receptor mutants. Diagrams can be produced and downloaded to illustrate receptor residues (snake-plot and helix box diagrams) and relationships (phylogenetic trees). Reference (crystal) structure-based sequence alignments take into account helix bulges and constrictions, display statistics of amino acid conservation and have been assigned generic residue numbering for equivalent residues in different receptors. For an overview read the GPCRdb poster , articles or documentation .
The G α subunit will eventually hydrolyze the attached GTP to GDP by its inherent enzymatic activity, allowing it to re-associate with G βγ and starting a new cycle. A group of proteins called Regulator of G protein signalling (RGSs), act as GTPase-activating proteins (GAPs), are specific for G α subunits. These proteins accelerate the hydrolysis of GTP to GDP, thus terminating the transduced signal. In some cases, the effector itself may possess intrinsic GAP activity, which then can help deactivate the pathway. This is true in the case of phospholipase C -beta, which possesses GAP activity within its C-terminal region. This is an alternate form of regulation for the G α subunit. However, it should be noted that such G α GAPs do not have catalytic residues (specific amino acid sequences) to activate the G α protein. They work instead by lowering the required activation energy for the reaction to take place.