Identification of the region in the hCG cDNA associating its bioactivity by using biotechnology

异源二聚体糖蛋白激素hCG、LH、TSH和FSH由两个非共价连接的亚基α和β亚基组成。β亚基对每种激素都是特异性的，并负责生物特异性，但不同激素的β亚基显示出一定程度的结构同源性。CAGY（半胱氨酸-丙氨酸-甘氨酸-酪氨酸）区是在不同β亚基中同源并且在物种之外高度保守的氨基酸序列之一。在本研究中，我们使用位点特异性体外诱变改变三个单独的核苷酸在中心的CAGY区域的hCG β亚基，并确定这些突变对hCG生产的影响，通过体外转录，然后在非洲爪蟾卵母细胞翻译。结果表明，CAGY区域，特别是β亚基中36位的甘氨酸残基，对于hCG的产生是必需的。这一发现与先前的研究一致，表明该区域是hTSH生物活性所必需的。

The heterodimeric glycoprotein hormones, hCG, LH, TSH and FSH consist of two noncovalently linked subunits, the alpha and beta subunits. The beta subunit is specific for each hormone and is responsible for the biological specificity, but the beta subunits of different hormones show some degree of structural homology. The CAGY (cysteine-alanine-glycine-tyrosine) region is one of the amino acid sequences that is homologous in different beta subunits and is highly conserved beyond species. In the present study, we used site-specific in vitro mutagenesis to change three individual nucleotides in the center of the CAGY region of the hCG beta subunit, and determined the effects of these mutations on hCG production by in vitro transcription and then translation in Xenopus oocytes. The results indicated that the CAGY region, particularly the glycine residue at position 36 in the beta subunit, is essential for the production of hCG. This finding is consistent with previous studies showing that this region is necessary for the biological activity of hTSH.