Catalytic domain of G protein-coupled Receptor Kinase 4-like Serine/Threonine Kinases
STKs catalyze the transfer of the gamma-phosphoryl group from ATP to serine/threonine residues on protein substrates. Members of the GRK4-like group include GRK4, GRK5, GRK6, and similar GRKs. They contain an N-terminal RGS homology (RH) domain and a catalytic domain, but lack a G protein betagamma-subunit binding domain. They are localized to the plasma membrane through post-translational lipid modification or direct binding to PIP2. GRKs phosphorylate and regulate G protein-coupled receptors (GPCRs), the largest superfamily of cell surface receptors which regulate some part of nearly all physiological functions. Phosphorylated GPCRs bind to arrestins, which prevents further G protein signaling despite the presence of activating ligand. The GRK4-like subfamily is part of a larger superfamily that includes the catalytic domains of other STKs, protein tyrosine kinases, RIO kinases, aminoglycoside phosphotransferase, choline kinase, and phosphoinositide 3-kinase.
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