The Human Follitropin -Subunit C Terminus Collaborates with a 
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- 作者：Carrie J. Arnold ; Cheng Liu ; Barbara Lindau-Shepard ; Michele L. Losavio ; Maria T. Patrascu ; and James A. Dias
- 刊名：Biochemistry
- 出版年：1998
- 出版时间：February 17, 1998
- 年：1998
- 卷：37
- 期：7
- 页码：1762 - 1768
- 全文大小：204K
- 年卷期：v.37,no.7(February 17, 1998)
- ISSN：1520-4995
文摘
FSH is a member of the pituitary/placentalglycoprotein hormone family including luteinizinghormone, thyroid-stimulating hormone, and chorionic gonadotropin.These heterodimeric hormones sharea common 
-subunit and a highly homologous but distinct 
-subunit.The determinant loop of the FSH-subunit acts both as a specificity discriminator and as anessential receptor-binding site. The three-dimensional structure of hCG illustrates the proximity of thedeterminant loop to the carboxyl-terminalresidues of the common -subunit. Thus, site-directedmutagenesis was used to make high-resolutionsubstitutions at this carboxyl-terminal locus. The effects ofthose substitutions were studied. Twelvesingle mutations and one composite mutation were made of the region ofhFSH 74-92, each residuesubstituted by alanine. Side chain replacement in this region ofFSH proved to be detrimental to binding.hFSH with mutations of either S85A, T86A, K91A, orS92A only retained 10% or less of thehFSH receptor-binding activity, while compared to these, mutantsH79A, Y88A, and Y89A retainedslightly more binding activity. The single mutant F74A andcomposite mutant V76A/E77A bindingactivity was reduced to half of that of wild-type (WT) hFSH. Incontrast, mutations of either K75A,T80A, H83A, or H90A did not adversely affect receptor binding,demonstrating the specificity ofobserved effects. The hFSH and mutant hormones were tested in anin vitro bioassay for stimulation ofprogesterone production. Those mutations that did not affectreceptor binding (K75A, T80A, H83A,and H90A) did not affect signal transduction, measured byprogesterone responses. After comparisonof wild-type and mutant hFSH activities determined in radioreceptorassays (ID50) and in vitro bioassays(ED50), it became evident that signal transductioncorrelated with receptor binding.
-subunit and a highly homologous but distinct -subunit.The determinant loop of the FSH-subunit acts both as a specificity discriminator and as anessential receptor-binding site. The three-dimensional structure of hCG illustrates the proximity of thedeterminant loop to the carboxyl-terminalresidues of the common -subunit. Thus, site-directedmutagenesis was used to make high-resolutionsubstitutions at this carboxyl-terminal locus. The effects ofthose substitutions were studied. Twelvesingle mutations and one composite mutation were made of the region ofhFSH 74-92, each residuesubstituted by alanine. Side chain replacement in this region ofFSH proved to be detrimental to binding.hFSH with mutations of either S85A, T86A, K91A, orS92A only retained 10% or less of thehFSH receptor-binding activity, while compared to these, mutantsH79A, Y88A, and Y89A retainedslightly more binding activity. The single mutant F74A andcomposite mutant V76A/E77A bindingactivity was reduced to half of that of wild-type (WT) hFSH. Incontrast, mutations of either K75A,T80A, H83A, or H90A did not adversely affect receptor binding,demonstrating the specificity ofobserved effects. The hFSH and mutant hormones were tested in anin vitro bioassay for stimulation ofprogesterone production. Those mutations that did not affectreceptor binding (K75A, T80A, H83A,and H90A) did not affect signal transduction, measured byprogesterone responses. After comparisonof wild-type and mutant hFSH activities determined in radioreceptorassays (ID50) and in vitro bioassays(ED50), it became evident that signal transductioncorrelated with receptor binding.