Phosphatidylinositol 4,5-Bisphosphate (PIP2)-enhanced G Protein-coupled Receptor Kinase (GRK) Activity: LOCATION, STRUCTURE, AND REGULATION OF THE PIP2 BINDING SITE DISTINGUISHES THE GRK SUBFAMILIES

Oct 4, 1996The Journal of biological chemistry

How a cell membrane lipid boosts receptor-regulating enzyme activity and differs between enzyme types in location, structure, and control

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Abstract

Phosphatidylinositol 4, 5-bisphosphate (PIP2) enhances GRK5-mediated phosphorylation of beta-adrenergic receptors by facilitating membrane association.

GRK5's phosphorylation activity is specifically enhanced by PIP2 through direct interaction, leading to improved receptor localization.
The phosphorylation of a soluble peptide substrate by GRK5 is not influenced by PIP2, indicating that enhanced activity is linked to membrane association.
A specific region in the amino terminus of GRK5 is critical for PIP2 binding, with mutations in this area abolishing its ability to interact with PIP2.
The PIP2 binding site in GRK5 shares similarities with that of gelsolin and is highly conserved among GRK4 subfamily members.
All members of the GRK4 subfamily (GRK4, GRK5, and GRK6) demonstrate PIP2-dependent receptor kinase activity.

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The G protein-coupled receptor kinases (GRKs) phosphorylate agonist occupied G protein-coupled receptors and play an important role in mediating receptor desensitization. The localization of these enzymes to their membrane incorporated substrates is required for their efficient function and appears to be a highly regulated process. In this study we demonstrate that phosphatidylinositol 4, 5-bisphosphate (PIP2) enhances GRK5-mediated beta-adrenergic receptor (betaAR) phosphorylation by directly interacting with this enzyme and facilitating its membrane association. GRK5-mediated phosphorylation of a soluble peptide substrate is unaffected by PIP2, suggesting that the PIP2-enhanced receptor kinase activity arises as a consequence of this membrane localization. The lipid binding site of GRK5 exhibits a high degree of specificity and appears to reside in the amino terminus of this enzyme. Mutation of six basic residues at positions 22, 23, 24, 26, 28, and 29 of GRK5 ablates the ability of this kinase to bind PIP2. This region of the GRK5, which has a similar distribution of basic amino acids to the PIP2 binding site of gelsolin, is highly conserved between members of the GRK4 subfamily (GRK4, GRK5, and GRK6). Indeed, all the members of the GRK4 subfamily exhibit PIP2-dependent receptor kinase activity. We have shown previously that the membrane association of betaARK (beta-adrenergic receptor kinase) (GRK2) is mediated, in vitro, by the simultaneous binding of PIP2 and the betagamma subunits of heterotrimeric G proteins to the carboxyl-terminal pleckstrin homology domain of this enzyme (Pitcher, J. A., Touhara, K., Payne, E. S., and Lefkowitz, R. J. (1995) J. Biol. Chem. 270, 11707-11710). Thus, five members of the GRK family bind PIP2, betaARK (GRK2), betaARK2 (GRK3), GRK4, GRK5, and GRK6. However, the structure, location, and regulation of the PIP2 binding site distinguishes the betaARK (GRK2 and GRK3) and GRK4 (GRK4, GRK5, and GRK6) subfamilies.

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Phosphatidylinositol 4,5-Bisphosphate (PIP2)-enhanced G Protein-coupled Receptor Kinase (GRK) Activity: LOCATION, STRUCTURE, AND REGULATION OF THE PIP2 BINDING SITE DISTINGUISHES THE GRK SUBFAMILIES

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