Figure 2.

The human Gαq polypeptide is 359 amino acids in length. It contains three α-helical domains called switch I (SWI), switch II (SWII) and switch III (SWIII) shown as patterned boxes. The location of amino acid residues R183 in SWI and Q209 in SWII are shown. The amino-terminal domain of Gαq interacts with PLCβ3[33]; Gαq activates PLCβ3 to hydrolyze PIP2 into inositol 1, 4, 5 triphosphate (IP3) and diacylglycerol (DAG). The SWI region changes conformation upon receptor binding; the SWII region interacts with the βγ subunits of the heterotrimer G-protein; and putative G-protein coupled receptor (GPCR) binding is located in the C-terminal region.