Pernollet J C, Garnier J, Pierce J G, Salesse R
Biochim Biophys Acta. 1976 Sep 28;446(1):262-76. doi: 10.1016/0005-2795(76)90117-3.
In vitro assembly of thyrotropin alpha and beta subunits led to an increase in content of alpha helix and beta sheet very similar to that found for gonadotropins. This association-dependent active folding involved the burying of three tyrosine residues tentatively assigned to Tyr alpha 41, Tyr beta 37 and Tyr beta 59 and common to all studied glycoprotein hormones. In vitro hybridizations between alpha and beta subunits of various hormones (thyrotropin, lutropin and choriogonadotropin) from different species (ovine, bovine and human) triggered the same molecular events as assembly of homologous subunits: the burying of three tyrosine residues and the increase of periodic structure of the folding. These changes are slow, time-dependent processes. Rates and yields of hybrid formation measured by sedimentation analysis and difference spectroscopy of tyrosines are identical, within experimental error, with the rates and yields measured by the recovery of the biological activity either the stimulation of chick thyroids for thyrotropin-beta hybrids or binding to porcine testis receptors for gonadotropin-beta hybrids. Whatever the origin of the alpha subunit, the thyrotropin-beta hybrids were not able to bind to testis receptors although active on chick thyroids. Rates and yields of hybrid formation essentially depended on the origin of the beta subunit. All the hybrids could be dissociated at acid pH with rates similar to those of native hormone. The extension to thyrotropin and various hybrids of the structural features of the in vitro assembly already recognized for gonadotropins strengthens the hypothesis that one deals with a basic activation process which also occurs in vivo after the synthesis of the subunits.
促甲状腺激素α亚基和β亚基的体外组装导致α螺旋和β折叠含量增加，这与促性腺激素的情况非常相似。这种依赖于亚基结合的活性折叠涉及到三个酪氨酸残基的埋藏，初步确定为Tyrα41、Tyrβ37和Tyrβ59，这三个酪氨酸残基在所有研究的糖蛋白激素中都存在。来自不同物种（绵羊、牛和人）的各种激素（促甲状腺激素、促黄体生成素和绒毛膜促性腺激素）的α亚基和β亚基之间的体外杂交引发了与同源亚基组装相同的分子事件：三个酪氨酸残基的埋藏以及折叠周期性结构的增加。这些变化是缓慢的、时间依赖性的过程。通过沉降分析和酪氨酸差示光谱法测量的杂交形成速率和产率，在实验误差范围内，与通过促甲状腺激素-β杂交体刺激鸡甲状腺或促性腺激素-β杂交体与猪睾丸受体结合来恢复生物活性所测量的速率和产率相同。无论α亚基的来源如何，促甲状腺激素-β杂交体虽然对鸡甲状腺有活性，但不能与睾丸受体结合。杂交形成的速率和产率基本上取决于β亚基的来源。所有杂交体在酸性pH下都可以解离，解离速率与天然激素相似。将已在促性腺激素中认识到的体外组装结构特征扩展到促甲状腺激素和各种杂交体，强化了这样一种假设，即这是一个基本的激活过程，在亚基合成后也会在体内发生。
