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Peptide inhibitors of GRK phosphorylation of rhodopsin

At present we know very little about the mechanism of allosteric activation of GRKs by GPCRs. To address this issue, we have developed a panel of peptides mimicking potential interaction sites. Here, we report the activity of five classes of peptides that inhibit rhodopsin phosphorylation by GRKs 5 and 7; namely mimetic of GRK5 α3, α9, and α10 helices in the RH domain, the N‐terminal peptide of GRK5, the C‐tail of transducin (TCT), and the first intracellular loop of the β2AR (il‐1 β2AR). Alanine scanning of α9 helix has revealed both essential and non‐essential residues for inhibition. Importantly R169A gave an IC50 of 4 μM resulting in a 12‐fold increase in potency for GRK inhibition relative to the native sequence. The peptide mimicking α10 helix inhibited both GRKs 5 and 7 activities (IC50 of 19 and 4 μM resp.). The peptide mimicking α3 helix inhibited GRK7 but not GRK5 activity. Further, the N‐terminal domain of GRK5, postulated to directly interact with rhodopsin and GRKs, inhibited both GRKs 5 and 7 (IC50 of 8 and 3 μM resp.). The TCT peptide, previously shown to inhibit rhodopsin activation of transducin, and the il‐1 β2AR peptide inhibited GRKs 5 and 7 activities. Our studies suggest potential GRK/GPCR interaction sites and provide lead peptides for potent specific inhibition of GPCR desensitization.