Structural diversity in the RGS domain and its interaction with heterotrimeric G protein α-subunits

doi:10.1073/pnas.0801508105

Structural diversity in the RGS domain and its interaction with heterotrimeric G protein α-subunits

*Structural Genomics Consortium, Oxford University, Oxford OX3 7DQ, United Kingdom;
^†Department of Pharmacology, University of North Carolina, Chapel Hill, NC 27599; and
^‡Leibniz-Institut für Molekulare Pharmakologie, Robert-Rössle Strasse 10, 13125 Berlin, Germany

Communicated by Melvin I. Simon, California Institute of Technology, Pasadena, CA, February 14, 2008 (received for review December 18, 2007)

Abstract

Regulator of G protein signaling (RGS) proteins accelerate GTP hydrolysis by Gα subunits and thus facilitate termination of signaling initiated by G protein-coupled receptors (GPCRs). RGS proteins hold great promise as disease intervention points, given their signature role as negative regulators of GPCRs—receptors to which the largest fraction of approved medications are currently directed. RGS proteins share a hallmark RGS domain that interacts most avidly with Gα when in its transition state for GTP hydrolysis; by binding and stabilizing switch regions I and II of Gα, RGS domain binding consequently accelerates Gα-mediated GTP hydrolysis. The human genome encodes more than three dozen RGS domain-containing proteins with varied Gα substrate specificities. To facilitate their exploitation as drug-discovery targets, we have taken a systematic structural biology approach toward cataloging the structural diversity present among RGS domains and identifying molecular determinants of their differential Gα selectivities. Here, we determined 14 structures derived from NMR and x-ray crystallography of members of the R4, R7, R12, and RZ subfamilies of RGS proteins, including 10 uncomplexed RGS domains and 4 RGS domain/Gα complexes. Heterogeneity observed in the structural architecture of the RGS domain, as well as in engagement of switch III and the all-helical domain of the Gα substrate, suggests that unique structural determinants specific to particular RGS protein/Gα pairings exist and could be used to achieve selective inhibition by small molecules.

Footnotes

^¶To whom correspondence may be addressed at:
Old Road Campus Research Building, Roosevelt Drive, Oxford University, Oxford OX3 7DQ, United Kingdom.
E-mail: declan.doyle{at}sgc.ox.ac.uk
^‖To whom correspondence may be addressed at:
Department of Pharmacology, University of North Carolina, Campus Box 7365, 1106 Mary Ellen Jones Building, Chapel Hill, NC 27599.
E-mail: dsiderov{at}med.unc.edu
Author contributions: M. Soundararajan, F.S.W., A.J.K., D.A.D., and D.P.S. designed research; M. Soundararajan, F.S.W., A.J.K., A.P.T., L.J.B., G.A.S., C.G., O.Y.F., E.F.D., V.A.H., and S.Q.H. performed research; F.S.W. and A.J.K. contributed new reagents/analytic tools; M. Soundararajan, F.S.W., A.J.K., A.P.T., and D.P.S. analyzed data; and M. Soundararajan, F.S.W., A.J.K., M. Sundström, and D.P.S. wrote the paper.
↵ ^§Present Address: Novo Nordisk Foundation Center for Protein Research, University of Copenhagen, Blegdamsvej 3B, DK-2200 Copenhagen N, Denmark.
The authors declare no conflict of interest.
Data deposition: The atomic coordinates and structure factors have been deposited in the Protein Data Bank, www.pdb.org [PDB ID codes 1ZV4, 2A72, 2AF0, 2BT2, 2BV1, 2ES0, 2GTP, 2IHB, 2IHD, 2IK8, and 2ODE (crystal structures); 2I59, 2JM5, 2JNU, and 2OWI (NMR structures)].
This article contains supporting information online at www.pnas.org/cgi/content/full/0801508105/DCSupplemental.
↵ ‖ Ingi et al. (19) and Cladman and Chidiac (20) have shown that, in a membrane reconstitution system with GPCR and Gαβγ heterotrimer present, RGS2 can serve as an efficient GAP for Gα_i subunits. The reason for the discrepancy between solution-based and membrane-based assays of Gα selectivity is as yet unresolved, but it is of note that RGS2 has multiple GAP-independent effects on GPCR function and signal transduction (42).