Analysis of G-protein-coupled receptor kinase RGS homology domains.

G-protein-coupled receptor kinases (GRKs) specifically phosphorylate agonist-occupied G-protein-coupled receptors (GPCRs). All seven mammalian GRKs contain an N-terminal domain that is homologous to the regulator of G-protein signaling (RGS) family of proteins. The RGS domain of GRK2 has been shown to interact specifically with Galphaq family members. While the specificity and functional consequences of GRK/Galpha interaction remain somewhat poorly defined, GRK RGS homology (RH) domains likely function to provide specificity for GRK interaction with a particular Galpha subunit or GPCR/Galpha complex. Indeed, GRK2 binds Galphaq, alpha11, and alpha14, but not Galpha16, Galphas, Galphai, or Galpha(12/13), while the RGS domains of GRK5 and GRK6 do not bind Galpha(q/11), Galphas, Galphai, or Galpha(12/13). In this chapter we describe various in vitro and intact cell strategies that can be used to elucidate the function of GRK RH domains.