Bonomi Marco, Busnelli Marta, Persani Luca, Vassart Gilbert, Costagliola Sabine
Institut de Recherche Interdisciplinaire en Biologie Humaine et Moléculaire, Université Libre de Bruxelles, Belgium.
Mol Endocrinol. 2006 Dec;20(12):3351-63. doi: 10.1210/me.2005-0521. Epub 2006 Aug 10.
Tyrosine sulfation is a late posttranslational modification of proteins that takes place in the Golgi network. In the past few years, this process has been identified as an important modulator of protein-protein interactions. Sulfated tyrosine residues have recently been identified in the C-terminal, so-called hinge region of the ectodomain of glycoprotein hormone receptors [TSH, LH/chorionic gonadotropin (CG), and FSH receptors] and were shown to play an important role in the interaction with their natural ligands. The position of two sulfated tyrosine residues in a Y-D/E-Y motif appears perfectly conserved in the alignment of TSH and LH receptors from different species, and site-directed mutagenesis experiments demonstrated that sulfation of the first residue of this motif was responsible for the functional effect on hormone binding. In contrast, the corresponding motif is not conserved in the FSH receptor, in which the first tyrosine residue is missing: the Y-D/E-Y motif is replaced by F(333)DY(335). We extend here our previous observation that, in this case, it is sulfation of the second sole tyrosine residue in the motif that is functionally important. An LH/CG receptor harboring an F(331)DY(333) motif (i.e. displaying decreased sensitivity to human CG) was used as a backbone in which short portions of the FSH receptor were substituted. Segments from the FSH receptor capable of restoring sensitivity to human CG were identified by transfection of the chimeras in COS-7 cells. These experiments identified key amino acid residues in the hinge region of the FSH receptor associated with the functional role of the second sulfated tyrosine residue in a Y-D/E-Y motif, allowing for efficient hormone binding. The experiments represent strong evidence that structural differences in the hinge regions of FSH and LH/CG receptors play a significant role in hormone-receptor-specific recognition.
酪氨酸硫酸化是一种发生在高尔基体网络中的蛋白质翻译后晚期修饰。在过去几年中，这一过程已被确定为蛋白质-蛋白质相互作用的重要调节因子。最近在糖蛋白激素受体[促甲状腺激素（TSH）、促黄体生成素/绒毛膜促性腺激素（CG）和促卵泡激素受体]胞外域的C末端（即所谓的铰链区）中发现了硫酸化酪氨酸残基，并且已证明其在与天然配体的相互作用中发挥重要作用。在来自不同物种的TSH和LH受体序列比对中，Y-D/E-Y基序中两个硫酸化酪氨酸残基的位置似乎完全保守，定点诱变实验表明，该基序中第一个残基的硫酸化对激素结合具有功能效应。相比之下，相应的基序在促卵泡激素受体中并不保守，其中第一个酪氨酸残基缺失：Y-D/E-Y基序被F(333)DY(335)取代。我们在此扩展我们之前的观察结果，即在这种情况下，该基序中唯一的第二个酪氨酸残基的硫酸化在功能上很重要。一个带有F(331)DY(333)基序（即对人CG敏感性降低）的LH/CG受体被用作骨架，其中替换了促卵泡激素受体的短片段。通过在COS-7细胞中转染嵌合体，鉴定出了促卵泡激素受体铰链区中与Y-D/E-Y基序中第二个硫酸化酪氨酸残基的功能作用相关的关键氨基酸残基，从而实现高效的激素结合。这些实验有力地证明，促卵泡激素和LH/CG受体铰链区的结构差异在激素-受体特异性识别中起重要作用。
