The functions of G-protein-coupled receptors (GPCRs) are primarily mediated and modulated by three families of proteins: the heterotrimeric G proteins, the G-protein-coupled receptor kinases (GRKs) and the arrestins1. G proteins mediate activation of second-messenger-generating enzymes and other effectors, GRKs phosphorylate activated receptors2, and arrestins subsequently bind phosphorylated receptors and cause receptor desensitization3. Arrestins activated by interaction with phosphorylated receptors can also mediate G-protein-independent signalling by serving as adaptors to link receptors to numerous signalling pathways4. Despite their central role in regulation and signalling of GPCRs, a structural understanding of β-arrestin activation and interaction with GPCRs is still lacking. Here we report the crystal structure of β-arrestin-1 (also called arrestin-2) in complex with a fully phosphorylated 29-amino-acid carboxy-terminal peptide derived from the human V2 vasopressin receptor (V2Rpp). This peptide has previously been shown to functionally and conformationally activate β-arrestin-1 (ref. 5). To capture this active conformation, we used a conformationally selective synthetic antibody fragment (Fab30) that recognizes the phosphopeptide-activated state of β-arrestin-1. The structure of the β-arrestin-1–V2Rpp–Fab30 complex shows marked conformational differences in β-arrestin-1 compared to its inactive conformation. These include rotation of the amino- and carboxy-terminal domains relative to each other, and a major reorientation of the ‘lariat loop’ implicated in maintaining the inactive state of β-arrestin-1. These results reveal, at high resolution, a receptor-interacting interface on β-arrestin, and they indicate a potentially general molecular mechanism for activation of these multifunctional signalling and regulatory proteins.
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Protein Data Bank
Coordinates and structure factors for the b-arrestin-1–V2Rpp– Fab30 complex are deposited in the Protein Data Bank under accession code 4JQI.
We thank D. Capel for technical assistance and V. Ronk, D. Addison and Q. Lennon for administrative and secretarial support. We thank S. Ahn and L. Wingler for critical reading of the manuscript. We acknowledge support from the Stanford Medical Scientist Training Program and the American Heart Association (A.M.), from the National Science Foundation (A.C.K.), from the National Institutes of Health Grants NS028471 (B.K.K.), HL16037 and HL70631 (R.J.L.), GM072688 and GM087519 (A.A.K. and S.K.), HL 075443 (K.X.) and from the Mathers Foundation (B.K.K. and W.I.W.). R.I.R is supported by a post-doctoral fellowship from Coordenação de Aperfeiçoamento de Pessoal de Nível Superior–CAPES. R.J.L. is an investigator with the Howard Hughes Medical Institute.
This file contains Supplementary Figures 1-7, Supplementary Methods, Supplementary Table 1 and Supplementary References.