The lutropin/choriogonadotropin receptor (LH/CG-R) is a G protein-coupled receptor with a relatively large extracellular domain. The cDNAs of LH/CG-R wild type and 15 point and double mutants, which encoded residues of opposite charge to that of wild type, were transiently transfected into COS-7 cells. Human choriogonadotropin (hCG) binding was determined, as was hCG-mediated cAMP production. Most of the replacements resulted in no substantive effect on the binding affinity of hCG to LH/CG-R or on hCG-stimulated cAMP production, although the mutants expressed at a lower level than LH/CG-R wild type. The most interesting observation was noted with two point mutants of LH/CG-R, Glu Lys and Asp Lys, which bound hCG but failed to give increased cAMP production. Several of the mutant forms of LH/CG-R that expressed at low levels were further analyzed by soluble binding assays and Western blots. There was no evidence of any significant degree of intracellular trapping of hCG-binding mutant receptors. The expected major (93 kDa) and minor (78 kDa) forms were found for LH/CG-R wild type and several of the mutants. The Lys Asp and Asp Lys mutants exhibited primarily the lower M form, indicating that receptor processing was impaired or that the mutant higher M form was more rapidly degraded than LH/CG-R wild type. These results demonstrate that Glu and Asp, which are located near the first transmembrane helix, are important in receptor activation, while other conserved ionizable residues of LH/CG-R appear important in cell surface expression or stability but not in binding or signaling.

CiteULike

Complore

Connotea

Del.icio.us

Digg

Reddit

Technorati

This article has been cited by other articles:

				G. Kleinau and G. Krause Thyrotropin and Homologous Glycoprotein Hormone Receptors: Structural and Functional Aspects of Extracellular Signaling Mechanisms Endocr. Rev., April 1, 2009; 30(2): 133 - 151. [Abstract] [Full Text] [PDF]

				R. L. Schubert, P. Narayan, and D. Puett Specificity of Cognate Ligand-Receptor Interactions: Fusion Proteins of Human Chorionic Gonadotropin and the Heptahelical Receptors for Human Luteinizing Hormone, Thyroid-Stimulating Hormone, and Follicle-Stimulating Hormone Endocrinology, January 1, 2003; 144(1): 129 - 137. [Abstract] [Full Text] [PDF]

				J. W. M. Martens, S. Lumbroso, M. Verhoef-Post, V. Georget, A. Richter-Unruh, M. Szarras-Czapnik, T. E. Romer, H. G. Brunner, A. P. N. Themmen, and Ch. Sultan Mutant Luteinizing Hormone Receptors in a Compound Heterozygous Patient with Complete Leydig Cell Hypoplasia: Abnormal Processing Causes Signaling Deficiency J. Clin. Endocrinol. Metab., June 1, 2002; 87(6): 2506 - 2513. [Abstract] [Full Text] [PDF]

				A. P. N. Themmen and I. T. Huhtaniemi Mutations of Gonadotropins and Gonadotropin Receptors: Elucidating the Physiology and Pathophysiology of Pituitary-Gonadal Function Endocr. Rev., October 1, 2000; 21(5): 551 - 583. [Abstract] [Full Text]

				N. Bhowmick, P. Narayan, and D. Puett Identification of Ionizable Amino Acid Residues on the Extracellular Domain of the Lutropin Receptor Involved in Ligand Binding Endocrinology, October 1, 1999; 140(10): 4558 - 4563. [Abstract] [Full Text]

				C. A. Alvarez, P. Narayan, J. Huang, and D. Puett Characterization of a Region of the Lutropin Receptor Extracellular Domain Near Transmembrane Helix 1 That Is Important in Ligand-Mediated Signaling Endocrinology, April 1, 1999; 140(4): 1775 - 1782. [Abstract] [Full Text]

				S. Y. Hsu, S.-G. Liang, and A. J. W. Hsueh Characterization of Two LGR Genes Homologous to Gonadotropin and Thyrotropin Receptors with Extracellular Leucine-Rich Repeats and a G Protein-Coupled, Seven-Transmembrane Region Mol. Endocrinol., December 1, 1998; 12(12): 1830 - 1845. [Abstract] [Full Text]

				S. S. Stavrou, Y.-S. Zhu, L.-Q. Cai, M. D. Katz, C. Herrera, M. DeFillo-Ricart, and J. Imperato-McGinley A Novel Mutation of the Human Luteinizing Hormone Receptor in 46XY and 46XX Sisters J. Clin. Endocrinol. Metab., June 1, 1998; 83(6): 2091 - 2098. [Abstract] [Full Text]

				K. Ryu, H. Lee, S. Kim, J. Beauchamp, C.-S. Tung, N. W. Isaacs, I. Ji, and T. H. Ji Modulation of High Affinity Hormone Binding. HUMAN CHORIOGONADOTROPIN BINDING TO THE EXODOMAIN OF THE RECEPTOR IS INFLUENCED BY EXOLOOP 2 OF THE RECEPTOR J. Biol. Chem., March 13, 1998; 273(11): 6285 - 6291. [Abstract] [Full Text] [PDF]

				F.-P. Zhang, A. S. Rannikko, P. R. Manna, H. M. Fraser, and I. T. Huhtaniemi Cloning and Functional Expression of the Luteinizing Hormone Receptor Complementary Deoxyribonucleic Acid from the Marmoset Monkey Testis: Absence of Sequences Encoding Exon 10 in Other Species Endocrinology, June 1, 1997; 138(6): 2481 - 2490. [Abstract] [Full Text] [PDF]

				S. Hong, K.-S. Ryu, M.-S. Oh, I. Ji, and T. H. Ji Roles of Transmembrane Prolines and Proline-induced Kinks of the Lutropin/Choriogonadotropin Receptor J. Biol. Chem., February 14, 1997; 272(7): 4166 - 4171. [Abstract] [Full Text] [PDF]

				C. Wu, P. Narayan, and D. Puett Protein Engineering of a Novel Constitutively Active Hormone-Receptor Complex J. Biol. Chem., December 6, 1996; 271(49): 31638 - 31642. [Abstract] [Full Text] [PDF]

				R. L. Gilchrist, K.-S. Ryu, I. Ji, and T. H. Ji The Luteinizing Hormone/Chorionic Gonadotropin Receptor Has Distinct Transmembrane Conductors for cAMP and Inositol Phosphate Signals J. Biol. Chem., August 9, 1996; 271(32): 19283 - 19287. [Abstract] [Full Text] [PDF]

				L. M. Fernandez and D. Puett Lys[IMAGE] in the Third Extracellular Loop of the Lutropin/Choriogonadotropin Receptor Is Critical for Signaling J. Biol. Chem., January 12, 1996; 271(2): 925 - 930. [Abstract] [Full Text] [PDF]

				Y. S. Song, I. Ji, J. Beauchamp, N. W. Isaacs, and T. H. Ji Hormone Interactions to Leu-rich Repeats in the Gonadotropin Receptors. I. ANALYSIS OF LEU-RICH REPEATS OF HUMAN LUTEINIZING HORMONE/CHORIONIC GONADOTROPIN RECEPTOR AND FOLLICLE-STIMULATING HORMONE RECEPTOR J. Biol. Chem., January 26, 2001; 276(5): 3426 - 3435. [Abstract] [Full Text] [PDF]

				S. D. Mahale, J. Cavanagh, A. Schmidt, R. MacColl, and J. A. Dias Autologous Biological Response Modification of the Gonadotropin Receptor J. Biol. Chem., April 6, 2001; 276(15): 12410 - 12419. [Abstract] [Full Text] [PDF]