Refining Efficacy: Allosterism and Bias in G Protein-Coupled Receptor Signaling

  • Louis M. LuttrellEmail author
  • Terry P. Kenakin
Part of the Methods in Molecular Biology book series (MIMB, volume 756)


Receptors on the surface of cells function as conduits for information flowing between the external environment and the cell interior. Since signal transduction is based on the physical interaction of receptors with both extracellular ligands and intracellular effectors, ligand binding must produce conformational changes in the receptor that can be transmitted to the intracellular domains accessible to G proteins and other effectors. Classical models of G protein-coupled receptor (GPCR) signaling envision receptor conformations as highly constrained, wherein receptors exist in equilibrium between single “off” and “on” states distinguished by their ability to activate effectors, and ligands act by perturbing this equilibrium. In such models, ligands can be classified based upon two simple parameters; affinity and efficacy, and ligand activity is independent of the assay used to detect the response. However, it is clear that GPCRs assume multiple conformations, any number of which may be capable of interacting with a discrete subset of possible effectors. Both orthosteric ligands, molecules that occupy the natural ligand-binding pocket, and allosteric modulators, small molecules or proteins that contact receptors distant from the site of ligand binding, have the ability to alter the conformational equilibrium of a receptor in ways that affect its signaling output both qualitatively and quantitatively. In this context, efficacy becomes pluridimensional and ligand classification becomes assay dependent. A more complete description of ligand–receptor interaction requires the use of multiplexed assays of receptor activation and screening assays may need to be tailored to detect specific efficacy profiles.

Key words

Agonist G protein-coupled receptor Heterotrimeric guanine nucleotide-binding protein Pharmaceutical chemistry Pharmacodynamics Signal transduction 



The Luttrell laboratory is supported by National Institutes of Health Grant DK55524 and the Research Service of the Charleston SC Veterans Affairs Medical Center.


  1. 1.
    Stephenson, R. P. (1956) A modification of receptor theory. Br J Pharmacol 11, 379–93.Google Scholar
  2. 2.
    Black, J. W., and Leff, P. (1983) Operational models of pharmacological agonist. Proc R Soc Lond [Biol] 220, 141–62.CrossRefGoogle Scholar
  3. 3.
    Black, J. W., Leff, P., and Shankley, N.P. (1985) An operational model of pharmacological agonism: The effect of E/[A] curve shape on agonist dissociation constant estimation. Br J Pharmacol 84, 561–71.CrossRefPubMedGoogle Scholar
  4. 4.
    Kenakin, T., and Miller, L. E. (2010) Seven transmembrane receptors as shapeshifting proteins: the impact of allosteric modulation and functional selectivity on new drug discovery. Pharmacol Rev. 62, 265–304.CrossRefPubMedGoogle Scholar
  5. 5.
    Koshland, D. E., Jr. (1998) Conformational changes: How small is big enough? Nature Med 4, 1112–4.CrossRefPubMedGoogle Scholar
  6. 6.
    Monod, J., Wyann, J., and Changeux, J-P. (1965) On the nature of allosteric transitions: a plausible model. J Mol Biol 12, 88–118.CrossRefPubMedGoogle Scholar
  7. 7.
    Karlin, A. (1967). On the application of “a plausible model” of allosteric proteins to the receptor for acetylcholine. J Theor Biol 16, 306–320.CrossRefPubMedGoogle Scholar
  8. 8.
    Thron, C.D. (1973) On the analysis of pharmacological experiments in terms of an allosteric receptor model. Mol Pharmacol 9, 1–9.PubMedGoogle Scholar
  9. 9.
    Okazaki, K-I., and Takada, S. (2008) Dynamic energy landscape view of coupled binding and protein conformational change: Induced-fit versus population shift models. Proc Natl Acad Sci USA 105, 11182–7.CrossRefPubMedGoogle Scholar
  10. 10.
    Kenakin, T. P. (1996) Receptor conformational induction versus selection: All part of the same energy landscape. Trends Pharmacol Sci. 17, 190–1.CrossRefGoogle Scholar
  11. 11.
    Palczewski, K., Kumasaka, T., Hori, T., Behnke, C. A., Motoshima, H., Fox, B. A., Trong, I. Le., Teller, D. C., Okada, T., Stenkamp, R. E., Yamamoto, M., and Miyano, M. (2000) Crystal structure of rhodopsin: a G protein-coupled receptor. Science 289:739–45.CrossRefPubMedGoogle Scholar
  12. 12.
    Okada, T., Sugihara, M., Bondar, A. N., Elstner, M., Entel, P., and Buss, V. (2004) The retinal conformation and its environment in rhodopsin in light of a new 2.2  Å crystal structure, J Mol Biol 342, 571–83.CrossRefPubMedGoogle Scholar
  13. 13.
    Salom, D., Lodowski, D. T., Stenkamp, R. E., Trong, I. Le, Golczak, M., Jastrzebska, B., Harris, T., Ballesteros, J. A., and Palczewski, K. (2006) Crystal structure of a photoactivated deprotonated intermediate of rhodopsin. Proc Natl Acad Sci U S A 103, 16123–8.CrossRefPubMedGoogle Scholar
  14. 14.
    Scheerer, P., Park, J. H., Hildebrand, P. W., Kim, Y. J., Krauss, N., Choe, H. W., Hofmann, K. P., and Ernst, O. P. (2008) Crystal structure of opsin in its G-protein-interacting conformation. Nature 455, 497–502.CrossRefPubMedGoogle Scholar
  15. 15.
    Gether, U., Lin, S., and Kobilka, B.K. (1995) Fluorescent labeling of purified β2 adrenergic receptor. Evidence for ligand-specific conformational changes. J Biol Chem 270, 28268–75.CrossRefPubMedGoogle Scholar
  16. 16.
    Ghanouni, P., Gryczynski, Z., Steenhuis, J.J., Lee, T.W., Farrens, D.L., Lakowicz, J.R., and Kobilka, B.K. (2001) Functionally different agonists induce distinct conformations in the G protein coupling domain of the β2 adrenergic receptor. J Biol Chem 276, 24433–6.CrossRefPubMedGoogle Scholar
  17. 17.
    Cherezov, V., Rosenbaum, D. M., Hanson, M. A., Rasmussen, S. G. F., Thian, F. S., Kobilka, T. S., Choi, H-J., Kuhn, P., Weis, W. I., Kobilka, B. K., and Stevens, R. C. (2007) High-resolution crystal structure of an engineered human β2-adrenergic G protein-coupled receptor. Science. 318, 1258–65.CrossRefPubMedGoogle Scholar
  18. 18.
    Rosenbaum, D. M., Cherezov, V., Hanson, M. A., Rasmussen, S. G. F., Thian, F. S., Kobilka, T. S., Choi, H-J., Yao, X-J., Weis, W. I., Stevens, R. C., and Kobilka, B. K. (2007) GPCR engineering yields high-resolution structural insights into β2-adrenergic receptor function. Science. 318, 1266–73.CrossRefPubMedGoogle Scholar
  19. 19.
    Rasmussen, S. G. F., Choi, H-J., Rosenbaum, D. M., Kobilka, T. S., Thian, F. S., Edwards, P. C., Burghammer, M., Ratnala, V. R. P., Sanishvili, R., Fischetti, R. F., Schertler, G. F. X., Weis, W. I., and Kobilka, B. K. (2007) Crystal structure of the human β2 adrenergic G-protein-coupled receptor. Nature 450, 383–7.CrossRefPubMedGoogle Scholar
  20. 20.
    Weis, W. I., and Kobilka, B. K. (2008) Structural insights into G-protein-coupled receptor activation. Curr Opin Struct Biol 18, 734–40.CrossRefPubMedGoogle Scholar
  21. 21.
    Allen, L. F., Lefkowitz, R. J., Caron, M. G., and Cotecchia, S. (1991) G-protein-coupled receptor genes as protooncogenes: constitutively activating mutation of the alpha 1B-adrenergic receptor enhances mitogenesis and tumorigenicity. Proc Natl Acad Sci U S A 88, 11354–8.CrossRefPubMedGoogle Scholar
  22. 22.
    Samama, P., Cotecchia, S., Costa, T., and Lefkowitz, R. J. (1993) A mutation-induced activated state of the beta 2-adrenergic receptor. Extending the ternary complex model. J Biol Chem 268, 4625–36.PubMedGoogle Scholar
  23. 23.
    Kosugi, S., Shenker, A., and Mori, T. (1994) Constitutive activation of cyclic AMP but not phosphatidylinositol signaling caused by four mutations in the 6th transmembrane helix of the human thyrotropin receptor. FEBS Lett 356, 291–4.CrossRefPubMedGoogle Scholar
  24. 24.
    Kosugi, S., Van Dop, C., Geffner, M. E., Rabl, W., Carel, J. C., Chaussain, J.L., Mori, T., Merendino, J. J. Jr., and Shenker, A. (1995) Characterization of heterogeneous mutations causing constitutive activation of the luteinizing hormone receptor in familial male precocious puberty. Hum Mol Genet 4, 183–8.CrossRefPubMedGoogle Scholar
  25. 25.
    Kjelsberg, M. A., Cotecchia, S., Ostrowski, J., Caron, M. G., and Lefkowitz, R. J. (1992) Constitutive activation of the alpha 1B-adrenergic receptor by all amino acid substitutions at a single site. Evidence for a region which constrains receptor activation. J Biol Chem 267, 1430–3.PubMedGoogle Scholar
  26. 26.
    Gether, U., Ballesteros, J. A., Seifert, R., Sanders-Bush, E., Weinstein, H., and Kobilka, B. K. (1997) Structural instability of a constitutively active G protein-coupled receptor. Agonist-independent activation due to conformational flexibility. J Biol Chem 272, 2587–90.CrossRefPubMedGoogle Scholar
  27. 27.
    Costa. T., and Herz, A. (1989) Antagonists with negative intrinsic activity at delta opioid receptors coupled to GTP-binding proteins. Proc Natl Acad Sci U S A 86, 7321–5.CrossRefPubMedGoogle Scholar
  28. 28.
    Weiss, J. M., Morgan, P. H., Lutz, M. W., and Kenakin, T. P. (1996) The cubic ternary complex receptor-occupancy model. III. resurrecting efficacy. J Theor Biol 181, 381–97.CrossRefPubMedGoogle Scholar
  29. 29.
    Kenakin T. (1995) Pharmacological proteus? Trends Pharmacol Sci 16, 256–8.CrossRefPubMedGoogle Scholar
  30. 30.
    Cordeaux, Y., Briddon, S. J., Megson, A. E., McDonnell, J., Dickenson, J. M., and Hill, S. J, (2000) Influence of receptor number on functional responses elicited by agonists acting at the human adenosine A(1) receptor: evidence for signaling pathway-dependent changes in agonist potency and relative intrinsic activity. Mol Pharmacol 58, 1075–84.PubMedGoogle Scholar
  31. 31.
    Zhu, X., Gilbert, S., Birnbaumer, M., and Birnbaumer, L. (1994) Dual signaling potential is common among Gs-coupled receptors and dependent on receptor density. Mol Pharmacol 46, 460–9.PubMedGoogle Scholar
  32. 32.
    Nasman, J., Kukkonen, J. P., Ammoun, S., and Akerman, K. E. (2001) Role of G-protein availability in differential signaling by α2-adrenoceptors. Biochem Pharmacol 62, 913–22.CrossRefPubMedGoogle Scholar
  33. 33.
    Offermanns, S., Wieland, T., Homann, D., Sandmann, J., Bombien, E., Spicher, K., Schultz, G., and Jakobs, K. H. (1994) Transfected muscarinic acetylcholine receptors selectively couple to Gi-type G proteins and Gq/11. Mol Pharmacol 45, 890–898.PubMedGoogle Scholar
  34. 34.
    Kenakin, T. (1995) Agonist-receptor efficacy. II. Agonist-trafficking of receptor signals. Trends Pharmacol Sci 16, 232–38.CrossRefPubMedGoogle Scholar
  35. 35.
    Meller, E., Puza, T., Diamond, J., Lieu, H. D., and Bohmaker, K. (1992) Comparative effects of receptor inactivation, 17 β-estradiol and pertussis toxin on dopaminergic inhibition of prolactin secretion in vitro. J Pharmacol Exp Ther 263, 462–9.PubMedGoogle Scholar
  36. 36.
    Spengler, D., Waeber, C., Pantaloni, C., Holsboer, F., Bockaert, J., Seeburg, P. H., and Journot, L. (1993) Differential signal transduction by five splice variants of the PACAP receptor. Nature 365, 170–5.CrossRefPubMedGoogle Scholar
  37. 37.
    Berg, K. A., Maayani, S., Goldfarb, J., Scaramellini, C., Leff, P., and Clarke, W. P. (1998) Effector pathway-dependent relative efficacy at serotonin type 2A and 2 C receptors: evidence for agonist-directed trafficking of receptor stimulus. Mol Pharmacol 54, 94–104.PubMedGoogle Scholar
  38. 38.
    Sagan, S., Chassaing, G., Pradier, L., and Lavielle, S. (1996) Tachykinin peptides affect differently the second messenger pathways after binding to CHO-expressed human NK-1 receptors. J Pharmacol Exp Ther 276, 1039–48.PubMedGoogle Scholar
  39. 39.
    Takasu, H., Gardella, T. J., Luck, M. D., Potts, J. T., and Bringhurst, F. R. (1999) Amino-terminal modifications of human parathyroid hormone (PTH) selectively alter phospholipase C signaling via the type 1 PTH receptor: Implications for design of signal-specific PTH ligands Biochemistry 38, 13453–60.CrossRefPubMedGoogle Scholar
  40. 40.
    Mohan, S., Kutilek, S., Zhang, C., Shen, H. G., Kodama, Y., Srivastava, A. K., Wergedal, J. E., Beamer, W. G., and Baylink, D. J. (2000) Comparison of bone formation responses to parathyroid hormone(1–34), (1–31), and (2–34) in mice. Bone 27, 471–8.CrossRefPubMedGoogle Scholar
  41. 41.
    Gray, J. A., and Roth, B. L. (2001) Paradoxical trafficking and regulation of 5-HT(2A) receptors by agonists and antagonists. Brain Res Bull 56, 441–51.CrossRefPubMedGoogle Scholar
  42. 42.
    Holloway, A. C., Qian, H., Pipolo, L., Ziogas, J., Miura, S., Karnik, S., Southwell, B. R., Lew, M. J., and Thomas, W. G. (2002) Side-chain substitutions within angiotensin II reveal different requirements for signaling, internalization and phosphorylation of type 1A angiotensin receptors. Mol Pharmacol 61 768–77.CrossRefPubMedGoogle Scholar
  43. 43.
    Sneddon, W. B., Magyar, C. E., Willick, G. E., Syme, C. A., Galbiati, F., Bisello, A., and Friedman, P. A. (2004) Ligand-selective dissociation of activation and internalization of the parathyroid hormone (PTH) receptor: conditional efficacy of PTH peptide fragments. Endocrinology 145, 2815–23.CrossRefPubMedGoogle Scholar
  44. 44.
    Bisello, A., Chorev, M., Rosenblatt, M., Monticelli, L., Mierke, D. F., and Ferrari, S. L. (2002) Selective ligand-induced stabilization of active and desensitized parathyroid hormone type 1 receptor conformations. J Biol Chem 277, 38524–30.CrossRefPubMedGoogle Scholar
  45. 45.
    Gesty-Palmer, D., Chen, M., Reiter, E., Ahn, S., Nelson, C. D., Wang, S., Eckhardt, A. E., Cowan, C. L., Spurney, R. F., Luttrell, L. M., and Lefkowitz, R. J. (2006) Distinct conformations of the parathyroid hormone receptor mediate G protein and beta-arrestin dependent activation of ERK1/2. J Biol Chem 281, 10856–64.CrossRefPubMedGoogle Scholar
  46. 46.
    Walters, R. W., Shukla, A. K., Kovacs, J. J., Violin, J. D., DeWire, S. M., Lam, C. M., Chen, J. R., Muehlbauer, M. J., Whalen, E. J., and Lefkowitz, R. J. (2009) beta-Arrestin1 mediates nicotinic acid-induced flushing, but not its antilipolytic effect, in mice. J Clin Invest 119, 1312–21.CrossRefPubMedGoogle Scholar
  47. 47.
    Seifert, R., Gether, U., Wenzel-Seifert, K., and Kobilka, B. K. (1999) Effects of guanine, inosine, and xanthine nucleotides on β(2)-adrenergic receptor/G(s) interactions: evidence for multiple receptor conformations. Mol Pharmacol 56, 348–58.PubMedGoogle Scholar
  48. 48.
    Perez, D. M., Hwa, J., Gaivin, R., Mathur, M., Brown, F. and Graham, R. M. (1996) Constitutive activation of a single effector pathway: evidence for multiple activation states of a G protein-coupled receptor. Mol Pharmacol 49, 112–22.PubMedGoogle Scholar
  49. 49.
    Barroso, S., Richard, F., Nicolas-Etheve, D., Kitabgi, P., and Labbe-Jullie, C. (2002) Constitutive activation of the neurotensin receptor 1 by mutation of Phe(358) in helix seven. Br J Pharmacol 135, 997–1002.CrossRefPubMedGoogle Scholar
  50. 50.
    Swaminath, G., Xiang, Y., Lee, T. W., Steenhuis, J., Parnot, C., and Kobilka, B. K. (2004) Sequential binding of agonists to the beta2 adrenoceptor. Kinetic evidence for intermediate conformational states. J Biol Chem 279, 686–91.CrossRefPubMedGoogle Scholar
  51. 51.
    Hruby, V. J., and Tollin, G. (2007) Plasmon-waveguide resonance (PWR) spectroscopy for directly viewing rates of GPCR/G-protein interactions and quantifying affinities. Curr Opin Pharmacol 7, 507–14.CrossRefPubMedGoogle Scholar
  52. 52.
    Vilardaga, J. P., Bunemann, M., Krasel, C., Castro, M., and Lohse, M. J. (2003) Measu-rement of the millisecond activation switch of G-protein-coupled receptors in living cells. Nat Biotechnol 21, 807–12.CrossRefPubMedGoogle Scholar
  53. 53.
    Swaminath, G., Deupi, X., Lee, T. W., Zhu, W., Thian, F. S., Kobilka, T. S., and Kobilka, B. (2005) Probing the β2-adrenoceptor binding site with catechol reveals diffe-rences in binding and activation by agonists and partial agonists. J Biol Chem 280, 22165–71.CrossRefPubMedGoogle Scholar
  54. 54.
    Zurn, A., Zabel, U., Vilardaga, J-P., Schindlein, H., Lohse, M. J., and Hoffmann, C. (2009) Fluorescence resonance energy transfer analysis of α2a-adrenergic receptoractivation reveals distinct agonist-specific conformational changes. Mol Pharmacol 75, 534–41.CrossRefPubMedGoogle Scholar
  55. 55.
    Galandrin, S., Oligny-Longpre, G., Bonin, H., Ogawa, K., Gales, C., and Bouvier, M. (2008) Conformational rearrangements and signaling cascades involved in ligand-based mitogen-activated protein kinase signaling through the β1-adrenergic recepor. Mol Pharmacol 74, 162–72.CrossRefPubMedGoogle Scholar
  56. 56.
    Baneres, J-L., Mesnier, D., Martin, A., Joubert, L., Dumuis, A., and Bockaret, J. (2005) Molecular characterization of a purified 5-HT4 receptor. J Biol Chem 280, 20253–60.CrossRefPubMedGoogle Scholar
  57. 57.
    Tutor, A., Penela, P., and Mayor, F. (2007) Anti-β1-adrenergic receptor autoantibodies are potent stimulators of the ERK1/2 pathway in cardiac cells. Cardiovasc Res 76, 51–60.CrossRefPubMedGoogle Scholar
  58. 58.
    Pellissier, L. P., Sallander, J., Campillo, M., Gaven, F., Queffeulou, E., Pillot, M., Dumuis, A., Claeysen, S., Bockaert, J., and Pardo, L. (2009) Conformational toggle switches implicated in basal constitutive and agonist-induced activated states of 5-hydroxytryptamine-4 receptors. Mol Phar-macol 75, 982–90.CrossRefPubMedGoogle Scholar
  59. 59.
    Whistler, J. L., Chuang, H. H., Chu, P., Jan, L.Y., and von Zastrow, M. (1999) Functional dissocation of mu opioid receptor signaling and endocytosis: implications for the biology of opiate tolerance and addiction. Neuron 23, 737–46.CrossRefPubMedGoogle Scholar
  60. 60.
    Jarpe, M. B., Knall, C., Mitchell, F. M., Buhl, A. M., Duzic, E., and Johnson, G. L. (1998) [D-Arg1,D-Phe5,D-Trp7,9,Leu11]Substance P acts as a biased agonist toward neuropeptide and chemokine receptors. J Biol Chem 273, 3097–104.CrossRefPubMedGoogle Scholar
  61. 61.
    Kudlacek, O., Waldoer, M., Kassack, M. U., Nickel, P., Salmi, J. I., Freissmuth, M., and Nanoff, C. (2002) Biased inhibition by a suramin analogue of A1-adenosine receptor/G protein coupling in fused receptor/G protein tandems: the A1 adenosine receptor is predominantly coupled to Goalpha in human brain. Naunyn Schmiedeberg’s Arch Pharmacol 365, 8–16.CrossRefGoogle Scholar
  62. 62.
    Manning, D. R. (2002) Measures of efficacy using G proteins as endpoints: differential engagement of G proteins through single receptors. Mol Pharmacol 62, 451–52.CrossRefPubMedGoogle Scholar
  63. 63.
    Gurwitz, D., Haring, R., Heldman, E., Fraser, C. M., Manor, D., and Fisher, A. (1994) Discrete activation of transduction pathways associated with acetylcholine M1 receptor by several muscarinic ligands. Eur J Pharmacol 267, 21–31.CrossRefPubMedGoogle Scholar
  64. 64.
    Lawler, C. P., Prioleau, C., Lewis, M. M., Mak, C., Jiang, D., Schetz, J. A., Gonzalez, A. M., Sibley, D. R., and Mailman, R. B. (1999) Interactions of the novel antipsychotic aripiprazole (OPC-14597) with dopamine and serotonin receptor subtypes. Neuropsychopharmacology 20, 612–27.CrossRefPubMedGoogle Scholar
  65. 65.
    Drake, M. T., Violin, J. D., Whalen, E. J., Wisler, J. W., Shenoy, S. K., and Lefkowitz, R. J. (2008) beta-Arrestin-biased agonism at the beta2-adrenergic receptor. J Biol Chem 283, 5669–76.CrossRefPubMedGoogle Scholar
  66. 66.
    Kenakin, T. P. (2007) Functional selectivity through protean and biased agonism: who steers the ship? Mol Pharmacol 72, 1393–401.CrossRefPubMedGoogle Scholar
  67. 67.
    Maudsley, S., Martin, B., and Luttrell, L. M. (2005) The origins of diversity and specificity in G protein-coupled receptor signaling. J Pharmacol Exp Ther 314, 485–94.CrossRefPubMedGoogle Scholar
  68. 68.
    Gesty-Palmer, D., and Luttrell, L. M. (2008) Heptahelical terpsichory. Who calls the tune? J Recept Signal Transduct Res 28, 39–58.CrossRefPubMedGoogle Scholar
  69. 69.
    Luttrell, L. M., and Gesty-Palmer, D. (2010) Beyond desensitization: physiological relevance of arrestin-dependent signaling. Pharmacol Rev 62, 305–30.CrossRefPubMedGoogle Scholar
  70. 70.
    Ferguson, S. S. (2001) Evolving concepts in G protein-coupled receptor endocytosis: the role in receptor desensitization and signaling. Pharm Rev 53, 1–24.PubMedGoogle Scholar
  71. 71.
    Luttrell, L. M., Ferguson, S. S. G., Daaka, Y., Miller, W. E., Maudsley, S., Della Rocca, G. J., Lin, F-T., Kawakatsu, H., Owada, K., Luttrell, D. K., Caron, M. G., and Lefkowitz, R. J. (1999) β-Arrestin-dependent formation of β2 adrenergic receptor/Src protein kinase complexes. Science 283, 655–61.CrossRefPubMedGoogle Scholar
  72. 72.
    Lefkowitz, R. J., and Shenoy, S. K. (2005) Transduction of receptor signals by beta-arrestins. Science. 308, 512–7.CrossRefPubMedGoogle Scholar
  73. 73.
    Wei, H., Ahn, S., Shenoy, S. K., Karnik, S., Hunyady, L., Luttrell, L. M., and Lefkowitz, R. J. (2003) Independent G protein and beta-arrestin2 mediated activation of ERK by angiotensin. Proc Natl Acad Sci USA 100, 10782–7.CrossRefPubMedGoogle Scholar
  74. 74.
    Azzi, M., Charest, P. G., Angers, S., Rousseau, G., Kohout, T., Bouvier, M., and Pineyro, G. (2003) Beta-arrestin-mediated activation of MAPK by inverse agonists reveals distinct active conformations for G protein-coupled receptors. Proc Natl Acad Sci USA 100, 11406–11.CrossRefPubMedGoogle Scholar
  75. 75.
    Wisler, J. W., DeWire, S. M., Whalen, E. J., Violin, J. D., Drake, M. T., Ahn, S., Shenoy, S. K., and Lefkowitz, R. J. (2007) A unique mechanism of beta-blocker action: carvedilol stimulates beta-arrestin signaling. Proc Natl Acad Sci USA 104, 16657–62.CrossRefPubMedGoogle Scholar
  76. 76.
    Ross, E. M., and Gilman, A. G. (1980) Biochemical properties of hormone-sensitive adenylate cyclase. Annu Rev Biochem. 49, 533–64.CrossRefPubMedGoogle Scholar
  77. 77.
    DeLean, A., Stadel, J.M., and Lefkowitz, R.J. (1980) A ternary complex model explains the agonist specific binding properties of the adenylate cyclase-coupled beta-adrenergic receptor. J Biol Chem 255, 7108–17.Google Scholar
  78. 78.
    Gurevich, V. V., Pals-Rylaarsdam, R., Benovic, J. L., Hosey, M. M., and Onorato, J. J. (1997) Agonist-receptor-arrestin, an alternative ternary complex with high agonist affinity. J Biol Chem 272, 28849–52.CrossRefPubMedGoogle Scholar
  79. 79.
    Key, T. A., Bennett, T. A., Foutz, T. D., Gurevich, V. V., Sklar, L. A., and Prossnitz, E. R. (2001) Regulation of formyl peptide receptor agonist affinity by reconstitution with arrestins and heterotrimeric G proteins. J Biol Chem 276, 49204–12.CrossRefPubMedGoogle Scholar
  80. 80.
    Kumar, S., Ma, B., Tsai, C-J., Sinha, N., and Nussinov, R. (2000) Folding and binding cascades: Dynamic landscapes and population shifts. Prot Sci 9, 10–9.CrossRefGoogle Scholar
  81. 81.
    Hilser, V. J., Garcia-Moreno, E. B., Oas, T. G., Kapp, G., and Whitten, S. T. (2006) A statistical thermodynamic model of protein ensembles. Chem Rev 106, 1545–58.CrossRefPubMedGoogle Scholar
  82. 82.
    Livesay, D. R., Dallakyan, S., Wood, G. G., and Jacobs, D. J. (2004) A flexible approach for understanding protein stability. FEBS Lett. 576, 468–76.CrossRefPubMedGoogle Scholar
  83. 83.
    Hilser, V. J., and Thompson, E. B. (2007) Intrinsic disorder as a mechanism to optimize allosteric coupling in proteins. Proc Natl Acad Sci USA 104, 8311–5.CrossRefPubMedGoogle Scholar
  84. 84.
    Kobilka, B. K., and Deupi, X. (2007) Conformational complexity of G-protein-coupled receptors. Trends Pharmacol Sci 28, 397–406.CrossRefPubMedGoogle Scholar
  85. 85.
    Devi, L. (2001) Heterodimerization of G-protein-coupled receptors: Pharmacology, signaling and trafficking. Trends Pharmacol Sci 22, 532–37.CrossRefPubMedGoogle Scholar
  86. 86.
    Milligan, G. (2001) Oligomerisation of G-protein-coupled receptors. J Cell Sci 114, 1265–71.PubMedGoogle Scholar
  87. 87.
    Angers, S., Salahpour, A., and Bouvier, M. (2002) Dimerization: An emerging concept for G protein-coupled receptor ontogeny and function. Ann Rev Pharmacol Toxicol 42, 409–35.CrossRefGoogle Scholar
  88. 88.
    Foord S. M., and Marshall, F. H. (1999) RAMPs: accessory proteins for seven transmembrane domain receptors. Trends Pharmacol Sci 20, 184–7.CrossRefPubMedGoogle Scholar
  89. 89.
    Hinkle, P. M., and Sebag, J. A. (2009) Structure and function of the melanocortin2 receptor accessory protein (MRAP). Mol Cell Endocrinol 300, 25–31.CrossRefPubMedGoogle Scholar
  90. 90.
    Brady, A. E., and Limbird, L. E. (2002) G protein-coupled receptor interacting proteins: emerging roles in localization and signal transduction. Cell Signal 14, 297–309.CrossRefPubMedGoogle Scholar
  91. 91.
    Bockaert, J, Marin, P, Dumuis, A and Fagni, L (2003) The “magic tail” of G protein-coupled receptors: An anchorage for functional protein networks. FEBS Lett 546, 65–72.CrossRefPubMedGoogle Scholar
  92. 92.
    Weinman, E. J., Hall, R. A., Friedman, P. A., Liu-Chen, L. Y., and Shenolikar, S. (2006) The association of NHERF adaptor proteins with G-protein-coupled receptors and receptor tyrosine kinases. Annu Rev Physiol 68, 491–505.CrossRefPubMedGoogle Scholar
  93. 93.
    Fredriksson, R., Lagerstrom, M. C., Lundin, L. G., and Schioth, H. B. (2003) The G-protein-coupled receptors in the human genome form five main families. Phylogenetic analysis, paralogon groups, and fingerprints. Mol. Pharmacol 63, 1256–72.Google Scholar
  94. 94.
    Jones, K. A., Borowsky, B., Tamm, J. A., Craig, D. A., Durkin, M. M., Dai, M., Yao, W. J., Johnson, M., Gunwaldsen, C., Huang, L. Y., Tang, C., Shen, Q., Salon, J. A., Morse, K., Laz, T., Smith, K. E., Nagarathnam, D., Noble, S. A., Branchek, T. A., and Gerald, C. (1998) GABA(B) receptors function as a heteromeric assembly of the subunits GABA(B)R1 and GABA(B)R2. Nature 396, 674–9.CrossRefPubMedGoogle Scholar
  95. 95.
    Kaupmann, K., Malitschek, B., Schuler, V., Heid, J., Froestl, W., Beck, P., Mosbacher, J., Bischoff, S., Kulik, A., Shigemoto, R., Karschin, A., and Bettler, B. (1998) GABA(B)-receptor subtypes assemble into functional heteromeric complexes. Nature. 396, 683–7.CrossRefPubMedGoogle Scholar
  96. 96.
    Margeta-Mitrovic, M., Jan, Y. N., and Jan, L. Y. (2000) A trafficking checkpoint controls GABA(B) receptor heterodimerization. Neuron 27, 97–106.CrossRefPubMedGoogle Scholar
  97. 97.
    Jordan, B. A., and Devi, L. A. (1999) G-protein-coupled receptor heterodimerization modulates receptor function. Nature 399, 697–700.CrossRefPubMedGoogle Scholar
  98. 98.
    Franco, R., Ferre, S., Agnati, L., Torvinen, M., Gines, S., Hillion, J., Casado, V., Lledo, P., Zoli, M., Lluis, C., and Fuxe, K. (2000) Evidence for adenosine/dopamine receptor interactions: indications for heteromerization. Neuropsychopharmacol 23, S50–9.CrossRefGoogle Scholar
  99. 99.
    Gomes, I., Jordan, B. A., Gupta, A., Trapaidze, N., Nagy, V., and Devi, L. A. (2000) Heterodimerization of μ and δ opioid receptors: A role in opiate synergy. J Neurosci 20, RC110.Google Scholar
  100. 100.
    AbdAlla, S., Lother, H., and Quitterer, U. (2000) AT1-receptor heterodimers show enhanced G-protein activation and altered receptor sequestration. Nature 407, 94–8.CrossRefPubMedGoogle Scholar
  101. 101.
    Barki-Harrington, L., Luttrell, L. M., and Rockman, H. A. (2003) Dual inhibition of beta-adrenergic and angiotensin II receptors by a single antagonist: A functional role for receptor-receptor interaction in vivo. Circulation. 108 1611–8.CrossRefPubMedGoogle Scholar
  102. 102.
    Rios, C., Gomes, I., and Devi, L. A. (2006) mu Opioid and CB1 cannabinoid receptor interactions: reciprocal inhibition of receptor signaling and neuritogenesis. Br J Pharmacol 148, 387–95.CrossRefPubMedGoogle Scholar
  103. 103.
    Mahon, M. J., Donowitz, M., Yun, C. C., and Segre, G. V. (2002) Na+/H+ exchanger regulatory factor 2 directs parathyroid hormone 1 receptor signalling. Nature 417, 858–61.CrossRefPubMedGoogle Scholar
  104. 104.
    Kenakin, T. P. (2009) 7TM receptor allostery: putting numbers to shapeshifting proteins. Trends Pharmacol Sci 30, 460–9.CrossRefPubMedGoogle Scholar
  105. 105.
    Wang, L., Martin, B., Brenneman, R., Luttrell, L. M., and Maudsley, S. (2009) Allosteric modulators of G protein-coupled receptors: future therapeutics for complex physiological disorders. J Pharmacol Exp Ther 331, 340–8.CrossRefPubMedGoogle Scholar
  106. 106.
    Ehlert F. J. (1988) Estimation of the affinities of allosteric ligands using radioligand binding and pharmacological null methods. Mol Pharmacol 33, 187–94.PubMedGoogle Scholar
  107. 107.
    Christopoulos, A., and Kenakin, T. (2002) G protein-coupled receptor allosterism and complexing. Pharmacol Rev 54, 323–74.CrossRefPubMedGoogle Scholar
  108. 108.
    Avlani, V., May, L. T., Sexton, P. M., and Christopoulos, A. (2004) Application of a kinetic model to the apparently complex behavior of negative and positive allosteric modulators of muscarinic acetylcholine receptors. J Pharmacol Exp Ther 308, 1062–72.CrossRefPubMedGoogle Scholar
  109. 109.
    Lanzafame, A., Christopoulos, A., and Mitchelson, F. (1997) Three allosteric modulators act at a common site, distinct from that of competitive antagonists, at muscarinic acetylcholine M2 receptors. J Pharmacol Exp Ther 282, 278–285.PubMedGoogle Scholar
  110. 110.
    Nemeth, E. F., Heaton, W. H., Miller, M., Fox, J., Balandrin, M. F., Van Wagenen, B. C., Colloton, M., Karbon, W., Scherrer, J., Shatzen, E., Rishton, G., Scully, S., Qi, M., Harris, R., Lacey, D., and Martin, D. (2004) Pharmacodynamics of the type II calcimimetic compound cinacalcet HCl. J Pharmacol Exp Ther 308 627–35.CrossRefPubMedGoogle Scholar
  111. 111.
    Price, M. R., Baillie, G. L., Thomas, A., Stevenson, L. A., Easson, M., Goodwin, R., McLean, A., McIntosh, L., Goodwin, G., Walker, G., Westwood, P., Marrs, J., Thomson, F., Cowley, P., Christopoulos, A., Pertwee, R. G., and Ross, R. A. (2005) Allosteric Modulation of the Cannabinoid CB1 Receptor. Mol Pharmacol 68, 1484–95.CrossRefPubMedGoogle Scholar
  112. 112.
    Knudsen, L. B., Kiel, D., Teng, M., Behrens, C., Bhumralkar, D., Kodra, J. T., Holst, J. J., Jeppesen, C. B., Johnson, M. D., de Jong, J. C., Jorgensen, A. S., Kercher, T., Kostrowicki, J., Madsen, P., Olesen, P. H., Petersen, J. S., Poulsen, F., Sidelmann, U. G., Sturis, J., Truesdale, L., May, J., and Lau, J. (2006) Small molecule agonists for the glucagon-like peptide 1 receptor. Proc Natl Acad Sci USA 104, 937–42.CrossRefGoogle Scholar
  113. 113.
    Langmead, C. J., Fry, V. A., Forbes, I. T., Branch, C. L., Christopoulos, A., Wood, M. D., and Herdon, H. J. (2006) Probing the molecular mechanism of interaction between 4-n-butyl-1-[4-(2-methylphenyl)-4-oxo-1-butyl]-piperidine (AC-42) and the muscarinic M1 receptor: direct pharmacological evidence that AC-42 is an allosteric agonist. Mol Pharmacol 69, 236–46.PubMedGoogle Scholar
  114. 114.
    Valant, C., Gregory, K. J., Hall, N. E., Scammells, P. J., Lew, M. J., Sexton, P. M., and Christopoulos, A. (2008) A novel mechanism of G protein-coupled receptor functional selectivity. Muscarinic partial agonist McN-A-343 as a bitopic orthosteric/allosteric ligand. J Biol Chem 283, 29312–21.CrossRefPubMedGoogle Scholar
  115. 115.
    Zhang, Y., Rodriguez, A., and Conn, P. J. (2005). Allosteric potentiators of metabotropic glutamate receptor subtype 5 have differential effects on different signaling pathways in cortical astrocytes. J Pharmacol Exp Ther 315, 1212–9.CrossRefPubMedGoogle Scholar
  116. 116.
    Sachpatzidis, A., Benton, B. K., Manfredi, J. P., Wang, H., Hamilton, A., Dohlman, H. G., and Lolis, E. (2003) Identification of allosteric peptide agonists of CXCR4. J Biol Chem 278, 896–907.CrossRefPubMedGoogle Scholar
  117. 117.
    Kondru, R., Zhang, J., Jim, C., Mirzadegan, T., Rotstein, D., Sankurati, S., and Dioszegi, M. (2008) Molecular interactions of CCR5 with major classes of small molecule anti-HIV CCR5 antagonists. Mol Pharmacol 73, 789–800.CrossRefPubMedGoogle Scholar
  118. 118.
    Maeda, K., Nakata, H., Koh, Y., Miyakawa, T., Ogata, H., Takaoka, Y., Sbibayama, S., Sagawa, K., Fukushima, D., Moravek, J., Koyanagi, Y., and Mitsuya, H. (2004) Spirodiketopiperazine based CCR5 inhibitor which preserves CC-chemokine/CCR5 interactions and exerts potent activity against R5 human immunodeficiency virus type 1 in vitro. J Virol 78, 8654–62.CrossRefPubMedGoogle Scholar
  119. 119.
    Watson, C., Jenkinson, S., Kazmierski, W., and Kenakin, T. P. (2005) The CCR5 receptor-based mechanism of action of 873140, a potent allosteric noncompetitive HIV entry-inhibitor. Mol Pharmacol 67, 1268–82.CrossRefPubMedGoogle Scholar
  120. 120.
    Muniz-Medina, V. M., Jones, S., Maglich, J. M., Galardi, C., Hollingsworth, R. E., Kazmierski, W. M., Ferris, R. G., Edelstein, M. P., Chiswell, K. E., and Kenakin, T. P. (2009) The relative activity of “function sparing” HIV-1 entry inhibitors on viral entry and CCR5 internalization: Is allosteric functional selectivity a valuable therapeutic property? Mol Pharmacol 75, 490–501.CrossRefPubMedGoogle Scholar
  121. 121.
    Wood A and Armour D. (2005). The discovery of the CCR5 receptor antagonist, UK-427,857, a new agent for the treatment of HIV infection and AIDS. Prog Med Chem. 43: 239–71.CrossRefPubMedGoogle Scholar
  122. 122.
    Lazareno, S., Popham, A., and Birdsall, N. J. M. (1998) Muscarinic interactions of bisindolylmaleimide analogues. Eur J Pharmacol 360, 281–4.CrossRefPubMedGoogle Scholar
  123. 123.
    Ellis, J., and Seidenberg, M. (2000) Interac-tions of alcuronium, TMB-8 and other allosteric ligands with muscarinic acetylcholine receptors: Studies with chimeric receptors. Mol Pharmacol 58, 1451–60.PubMedGoogle Scholar
  124. 124.
    Bridges, T. M., and Lindsley, C. W. (2008) G-protein-coupled receptors: from classical modes of modulation to allosteric mechanisms. ACS Chem Biol 3, 530–41.CrossRefPubMedGoogle Scholar
  125. 125.
    Ehlert, F. J. (2005) Analysis of Allosterism in Functional Assays. J Pharmacol Exp Ther 315, 740–54.CrossRefPubMedGoogle Scholar
  126. 126.
    Kenakin, T. (2007) Allosteric agonist modulators. J Recept Signal Transduct Res 27, 247–59.CrossRefPubMedGoogle Scholar
  127. 127.
    Leach, K., Sexton, P. M., and Christopoulos, A. (2007) Allosteric GPCR modulators: taking advantage of permissive receptor pharmacology. Trends Pharmacol Sci 28, 382–9.CrossRefPubMedGoogle Scholar
  128. 128.
    Maillet, E. L., Pellegrini, N., Valant, C., Bucher, B., Hibert, M., Bourguignon, J. J., and Galzi, J. L. (2007) A novel, conformation-specific allosteric inhibitor of the tachykinin NK2 receptor (NK2R) with functionally selective properties. FASEB J 21, 2124–34.CrossRefPubMedGoogle Scholar
  129. 129.
    Mathiesen, J. M., Ulven, T., Martini, L., Gerlach, L. O., Heinemann, A., and Kostenis, E. (2005) Identification of indole derivatives exclusively interfering with a G protein-independent signaling pathway of the prostaglandin D2 receptor CRTH2. Mol Pharmacol 68, 393–402.PubMedGoogle Scholar
  130. 130.
    Kew, J. N., Trube, G., and Kemp, J. A. (1996) A novel mechanism of activity-dependent NMDA receptor antagonism describes the effect of ifenprodil in rat cultured cortical neurones. J Physiol 497, 761–72.PubMedGoogle Scholar
  131. 131.
    Galandrin, S., and Bouvier, M. (2006) Distinct signaling profiles of beta1 and beta2 adrenergic receptor ligands toward adenylyl cyclase and mitogen-activated protein kinase reveals the pluridimensionality of efficacy. Mol Pharmacol 70, 1575–84.CrossRefPubMedGoogle Scholar
  132. 132.
    Watson, C., Chen, G., Irving, P. E., Way, J., Chen, W-J., and Kenakin, T. P. (2000) The use of stimulus-biased assay systems to detect agonist-specific receptor active states: Implications for the trafficking of receptor stimulus by agonists. Mol Pharmacol 58, 1230–8.PubMedGoogle Scholar
  133. 133.
    Woolf, P. J., Kenakin, T. P., and Linderman, J. J. (2001) Uncovering biases in high throughput screens of G-protein coupled receptors. J Theor Biol 208, 403–18.CrossRefPubMedGoogle Scholar
  134. 134.
    Chen, G., Way, J., Armour, S., Watson, C., Queen, K., Jayawickreme, C. K., Chen, W. J., and Kenakin, T. (2000) Use of constitutive G protein-coupled receptor activity for drug discovery. Mol Pharmacol 57, 125–34.PubMedGoogle Scholar
  135. 135.
    Gardella, T. J., Luck, M. D., Jensen, G. S., Schipani, E., Potts, J. T. Jr., Juppner, H. (1996) Inverse agonism of amino-terminally truncated parathyroid hormone (PTH) and PTH-related peptide (PTHrP) analogs revealed with constitutively active mutant PTH/PTHrP receptor. Endocrinology 137: 3936–3941.CrossRefPubMedGoogle Scholar
  136. 136.
    Shukla, A. K., Violin, J. D., Whalen, E. J., Gesty-Palmer, D., Shenoy, S. K., and Lefkowitz, R. J. (2008) Distinct conformational changes in beta-arrestin report biased agonism at seven-transmembrane receptors. Proc Natl Acad Sci USA 105, 9988–93.CrossRefPubMedGoogle Scholar
  137. 137.
    Gesty-Palmer, D., Flannery, P., Yuan, L., Spurney, R., Lefkowitz, R. J., and Luttrell, L. M. (2009) A beta-arrestin biased agonist of the parathyroid hormone receptor (PTH1R) promotes bone formation independent of G protein activation. Science – Transl Med 1:1ra1.Google Scholar
  138. 138.
    Leppik, R. A., and Birdsall, N. J. (2000) Agonist binding and function at the human α2A-adrenoceptor: allosteric modulation by amilorides. Mol Pharmacol 58, 1091–9.PubMedGoogle Scholar
  139. 139.
    Kenakin, T., Jenkinson, S., and Watson, C. (2006) Determining the potency and molecular mechanism of action of insurmountable antagonists. J Pharmacol Exp Ther 319, 710–23.CrossRefPubMedGoogle Scholar
  140. 140.
    Fang, Y., Ferrie, A. M., Fontaine, N. H., and Yuen, P. K. (2005) Characteristics of dynamic mass redistribution of EGF receptor signaling in living cells measured with label free optical biosensors. Anal Chem 77, 5720–5.CrossRefPubMedGoogle Scholar
  141. 141.
    Cunningham, B. T., Li, P., Schultz, S., Lin, B., Baird, C., Gerstenmaier, J., Genick, C., Wang, F., Fine, E., and Laing, L. (2004) Label free assays on the BIND system. J Biomolec Screen 9, 481–90.CrossRefGoogle Scholar
  142. 142.
    Fang, Y., and Ferrie, A. M. (2008) Label-free optical biosensor for ligand-directed functional selectivity acting on β2-adrenoceptor in living cells. FEBS Lett 582, 558–64.CrossRefPubMedGoogle Scholar
  143. 143.
    McGuinness, R. (2007) Impedance-based cellular assay technologies: Recent advances. Curr Opin Pharmacol 7, 535–40.CrossRefPubMedGoogle Scholar
  144. 144.
    Peters, M. F., and Scott, C. W. (2009) Evaluating cellular impedance assays for the detection of GPCR pleiotropic signaling and functional selectivity. J Biomol Screen 14, 246–55.CrossRefPubMedGoogle Scholar
  145. 145.
    Kenakin, T. (2005) New concepts in drug discovery: collateral efficacy and permissive antagonism. Nat Rev Drug Discov 4, 919–27.CrossRefPubMedGoogle Scholar
  146. 146.
    Milligan, G. (2003) High-content assays for ligand regulation of G-protein coupled receptors. Drug Disc Today 8, 579–85.CrossRefGoogle Scholar
  147. 147.
    Ross, D. A., Lee, S., Reiser, V., Xue, J., Alves, K., Vaidya, S., Kreamer, A., Mull, R., Hudak, E., Hare, T., Detmers, P. A., Lingham, R., Ferrer, M., Strulovici, B., and Santini, F. (2008) Mulitplexed assays by high-content imaging for assessment of GPCR activity. J Biomol Screen 13, 449–455.CrossRefPubMedGoogle Scholar
  148. 148.
    Ghosh, R. N., DeBasio, R., Hudson, C. C., Ramer, E. R., Cowan, C. L., and Oakley, R. H. (2005) Quantitative cell-based high content screening for vasopressin receptor agonists using Transfluor® technology. J Biomol Screen 10, 476–84.CrossRefPubMedGoogle Scholar
  149. 149.
    Hanson, B. J., Wetter, J., Bercherer, M. R., Kopp, L., Fuerstenau-Sharp, M., Vedvik, K. L., Zielinski, T., Doucette, C., Whitey, P. J., and Revankar, C. (2009) A homogeneous fluorescence live-cell assay for measuring 7-transmembrane receptor activity and agonist functional selectivity through beta-arrestin recruitment. J Biomol Screen 14, 798–810.CrossRefPubMedGoogle Scholar
  150. 150.
    Hamdan, F. F., Audet, M., Garneau, P., Pelletier, J., and Bouvier, M. (2005) High throughput screening of G-protein-coupled receptor antagonists using bioluminescence resonance energy transfer 1-based β-arrestin2 recruitment assay. J Biomol Screen 10, 463–75.CrossRefPubMedGoogle Scholar
  151. 151.
    Zhao, X., Jones, A., Olson, K. R., Peng, K., Wehrman, T., Park, A., Mallari, R., Nebalasca, D., Young, S. W., and Xiao, S-H. (2008) A homogeneous enzyme fragment complementation-based β-arrestin translocation assay for high throughput screening of G-protein-coupled receptors. J Biomol Screen 13, 737–47.CrossRefPubMedGoogle Scholar
  152. 152.
    Barnea, G., Strapps, W., Herrada, G., Berman, Y., Ong, J., Kloss, B., Axel, R., and Lee, K. J. (2008) The genetic design of signaling cascades to record receptor activation. Proc Natl Acad Sci USA 105, 64–9.CrossRefPubMedGoogle Scholar
  153. 153.
    Henriksen, U., Fog, J., Loechel, F., and Praestegaard, M. (2008) Profiling of multiple signal pathway activities by multiplexing antibody and GFP-based translocation assays. Comb Chem High Throughput Screen 11, 537–44.CrossRefPubMedGoogle Scholar
  154. 154.
    Groer, C. E., Tidgewell, K., Moyer, R. A., Harding, W. W., Rothman, R. B., Prisinzano, T. E., and Bohn, L. M. (2007) An opioid agonist that does not induce mu opioid receptor-arrestin interactions or receptor internalization. Mol Pharmacol 71, 549–557.CrossRefPubMedGoogle Scholar

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© Springer Science+Business Media, LLC 2011

Authors and Affiliations

  1. 1.Departments of Medicine and Biochemistry & Molecular BiologyMedical University of South CarolinaCharlestonUSA
  2. 2.Charleston VA Medical CenterCharlestonUSA
  3. 3.Department of PharmacologyUniversity of North Carolina, School of MedicineChapel HillUSA

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