Nov 15, 1989

Elimination of disulfide bonds affects assembly and secretion of the human chorionic gonadotropin beta subunit

The Journal of Biological Chemistry
N SuganumaI Boime


Human chorionic gonadotropin (hCG) consists of two noncovalently joined alpha and beta subunits similar to the other glycoprotein hormones. To study the function of the individual disulfide bonds in subunit assembly and secretion, site-directed mutagenesis was used to convert the 12 cysteine (Cys) residues in the beta subunit of hCG to either alanine or serine. Both cysteines of proposed disulfide pairs were also mutated. These mutant hCG beta genes were transfected alone or together with the wild-type alpha gene into Chinese hamster ovary cells. Only 3-10% assembly could be achieved with derivatives containing single Cys mutations at positions 26, 110, 72, and 90, whereas no assembly was detected with the other 8 mutants. However, double mutations of pairs 26-110 or 23-72 showed increased dimer formation (11 and 36%, respectively). The secretion rate of individual mutants varied significantly. Whereas the Cys-23 and 72 mutants were secreted normally (t1/2 = 140-190 min), the Cys-26 mutant was secreted faster (t1/2 = 70 min), and the other 9 mutants were secreted slower (t1/2 = 280-440 min); mutations of both Cys at 26 and 110 caused much faster secretion (t1/2 = 34 min). Although the secretion rate of these mutants differed, t...Continue Reading

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Mentioned in this Paper

Chorionic Gonadotropin, beta Subunit, Human
Shuttle Vectors
Post-Translational Protein Processing
Peptide Fragments
Protein Conformation
Restriction Mapping

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