EFFECT OF SITE-DIRECTED MUTAGENESIS IN THE CMGCC REGION OF THE ALPHA-SUBUNIT ON IMMUNOREACTIVE HUMAN THYROTROPIN

The cDNA of the common a-subunit of human glycoprotein hormone was mut ated by site directed mutagenesis in the CMGCC region compos ed of cys teine-methionine-glycine-cysteine-cysteine (position 28-32). The cDNA of wild-type human thyrotropin (hTSH) beta-subunit and that of wild-ty pe or mutant common alpha-subunits were co-transfected into COS-I cell s. The concentration of hTSH determined by two immunoradiometric assay systems was detectable in culture media of COS-I cells transfected wi th wild-type (CMGCC) and a mutant (C (R) under bar GCC) alpha-subunits but not four other mutants ((Y) under bar MGCC) (CM (R) under bar CC) (CM (A) under bar CC) (CM (D) under bar CC). The present data with th e other studies on wild-type or mutant glycoprotein hormones support o ur hypothesis that an amino acid motif of ''C-X-G-X-C'' in the common alpha-(CMGCC in human) and beta-(CAGYC in human) subunits play an impo rtant role in biosynthesis of glycoprotein hormones in all species.