Effect of Site Directed Mutagenesis in the CMGCC Region of the α-Subunit on Immunoreactive Human Thyrotropin

Abstract

The cDNA of the common α-subunit of human glycoprotein hormone was mutated by site directed mutagenesis in the CMGCC region composed of cysteine-methionine-glycine-cysteine-cysteine (position 28-32). The cDNA of wild-type human thyrotropin (hTSH) β-subunit and that of wild-type or mutant common α-subunits were co-transfected into COS-I cells. The concentration of hTSH determined by two immunoradiometric assay systems was detectable in culture media of COS-I cells transfected with wild-type (CMGCC) and a mutant (CMGCC) α-subunits but not four other mutants (YMGCC) (CMRCC) (CMACC) (CMGCC). The present data with the other studies on wild-type or mutant glycoprotein hormones support our hypothesis that an amino acid motif of “C-X-G-X-C” in the common α-(CMGCC in human) and β-(CAGYC in human) subunits play an important role in biosynthesis of glycoprotein hormones in all species.