Site-specific cleavage of G protein-coupled receptor-engaged beta-arrestin. Influence of the AT1 receptor conformation on scissile site selection.

The discovery of beta-arrestin-related approximately 46-kDa polypeptide in transfected cells and mouse hearts led us to examine angiotensin II type 1 receptor (AT(1)R)-dependent proteolytic cleavage of beta-arrestin(s). Receptor-ligand induced proteolysis of beta-arrestin(s) is novel, especially in the endocrine system, since proteolytic and/or splice variants of nonvisual arrestins are unknown. We used a strategy to retrieve AT(1)R-engaged isoforms of beta-arrestin 1 to confirm direct interaction of fragments with this G protein-coupled receptor and determine cleavage sites. Here we show that the angiotensin II-AT(1)R complex is associated with full-length and approximately 46-kDa beta-arrestin forms. Mass spectrometric analysis of the AT(1)R-associated short form suggested a scissile site located within the Arg(363)-Arg(393) region in the bovine beta-arrestin 1. Edman degradation analysis of a beta-arrestin 1 C-terminal fragment fused to enhanced green fluorescent protein confirmed the major cleavage to be after Phe(388) and a minor cleavage after Asn(375). Rather unexpectedly, the inverse agonist EXP3174-bound AT(1)R generated different fragmentation of bovine beta-arrestin 1, at Pro(276). The angiotensin II-induced cleavage is independent of inositol 1,4,5-trisphosphate- and Ca(2+)-mediated signaling pathways. The proteolysis of beta-arrestin 2 occurs, but the pattern is more complex. Our findings suggest that beta-arrestin cleavage upon AT(1)R stimulation is a part of the unraveling beta-arrestin-mediated G protein-coupled receptor signaling diversity.