title: A single amino acid residue replacement in the beta subunit of human chorionic gonadotrophin results in the loss of biological activity.
abstract: The heterodimer, human chorionic gonadotrophin (hCG), contains an alpha subunit that is common to the glycoprotein hormones and a hormone-specific beta subunit. A comparison of all known beta amino acid sequences shows that an aspartic acid at position 99 (with the numbering scheme for hCG-beta) is one of the seven non-Cys invariant residues. Using site-directed mutagenesis we have replaced hCG-beta Asp99 with Arg. Chinese hamster ovary cells, containing a stably integrated gene for bovine alpha subunit, were transiently transfected with plasmids containing wild-type and mutant hCG-beta cDNAs. The Arg99 beta mutant associated with the alpha subunit, but the resulting heterodimer failed to enhance intracellular cyclic AMP production in a gonadotrophin-responsive transformed murine Leydig cell line. Thus, a single amino acid residue replacement in this glycosylated heterodimer containing 237 amino acid residues is sufficient to abolish activity.
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Miami School of Medicine, Florida 33101.
authors.forename: F
authors.initials: F
authors.lastname: Chen
authors.forename: D
authors.initials: D
authors.lastname: Puett
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D016466:CHO Cells; D006063:Chorionic Gonadotropin / Q000235:genetics* / Q000494:pharmacology; D003001:Cloning, Molecular; D006224:Cricetinae; D000242:Cyclic AMP / Q000096:biosynthesis; D006801:Humans; D007985:Leydig Cells / Q000187:drug effects / Q000378:metabolism; D008297:Male; D016297:Mutagenesis, Site-Directed; D013329:Structure-Activity Relationship
chemical_list: D006063:Chorionic Gonadotropin; D000242:Cyclic AMP