STRUCTURE-FUNCTION STUDIES OF GONADOTROPINS

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The human placental hormone chorionic gonadotropin (hCG) together with the pituitary hormones lutropin (LH), follitropin (FSH), and thyrotropin (TSH) constitute a family of glycoprotein hormones of dimeric structure containing 2 nonidentical subunits, alpha and beta. Within an animal species the alpha subunits have an identical amino acid sequence; the hormones are distinguished by their unique beta subunits, which determine the biologic specificity of each hormone. Each hormone contains different asparaginelinked oligosaccharides. Using the techniques of DNA mediated transfection we will examine how different beta subunits influence assembly and processing of these multisubunit complexes. In combination with site directed mutagenesis and gene fusion experiments we will examine the following: (1) the influence of Nlinked carbohydrate on assembly, secretion, and disulfide bond formation. Does it account for some of the differences in the intracellular behavior of LH and CG-beta subunits that we have seen? (2) the role of the carboxyterminal sequence in the CGbeta subunit. For those subunits bearing two asparaginelinked sugar units, we will examine if there are different functional roles for each asparagine carbohydrate group, and (3) the effects of disrupting disulfide bonds on the metabolism and secretion of LH and hCG dimers/subunits. Site directed mutagenesis provides the most direct approach toward constructing a structurefunction map relating the dependence of posttranslational modifications, bioactivity, assembly and secretion on disulfide bond patterns.