Ji I, Ji T H
Department of Molecular Biology, University of Wyoming, Laramie 82071-3944.
Endocrinology. 1991 May;128(5):2648-50. doi: 10.1210/endo-128-5-2648.
We have reported that the rat LH receptor is encoded by 11 exons of a single copy gene. Exons 1-10 encode the N-terminal half and exon 11 the C-terminal half. Since exon splice sites often mark structural transitions of multiexon molecules, we have attempted to define the function of the exons by generating mutant receptors with missing exons. As a first step, we have constructed two LH mutant receptors, one containing exons 1-10 (LH receptor (exon)1-10) and the other containing exon 1 and exon 11 (LH receptor(exon)1&11). These mutant receptors were functionally expressed in Cos 7A cells. The LH mutant receptor(exon)1-10, which lacks the membrane associated C-terminal half of the receptor, showed a high affinity for hCG. Surprisingly, the LH mutant receptor(exon)1&11 recognized hCG with a low affinity and stimulated G-proteins and cAMP production. The results demonstrate that exons 1-10 encode a high affinity hCG binding site and proves an important hypothesis that exon 11 encodes the site for receptor-modulation to activate G-proteins. Furthermore, the results raises an intriguing possibility of a second hormone binding site in the C-terminal half and multistep hormone binding.
我们已报道大鼠促黄体生成素（LH）受体由一个单拷贝基因的11个外显子编码。外显子1至10编码N端的一半，外显子11编码C端的一半。由于外显子剪接位点常标志着多外显子分子的结构转变，我们试图通过构建缺失外显子的突变受体来确定外显子的功能。第一步，我们构建了两种LH突变受体，一种包含外显子1至10（LH受体（外显子）1 - 10），另一种包含外显子1和外显子11（LH受体（外显子）1&11）。这些突变受体在Cos 7A细胞中实现了功能性表达。缺乏受体膜相关C端一半的LH突变受体（外显子）1 - 10对人绒毛膜促性腺激素（hCG）显示出高亲和力。令人惊讶的是，LH突变受体（外显子）1&11以低亲和力识别hCG并刺激G蛋白和环磷酸腺苷（cAMP）的产生。结果表明外显子1至10编码一个高亲和力的hCG结合位点，并证明了一个重要的假说，即外显子11编码受体调节以激活G蛋白的位点。此外，结果还提出了C端一半存在第二个激素结合位点以及多步激素结合的有趣可能性。
