Nishi S, Hsu S Y, Zell K, Hsueh A J
Department of Gynecology and Obstetrics, Stanford University School of Medicine, California 94305-5317, USA.
Endocrinology. 2000 Nov;141(11):4081-90. doi: 10.1210/endo.141.11.7744.
The receptors for lutropin (LH), FSH, and TSH belong to the large G protein-coupled receptor (GPCR) superfamily and are unique in having a large N-terminal extracellular (ecto-) domain important for interactions with the large glycoprotein hormone ligands. Recent studies indicated the evolution of a large family of the leucine-rich repeat-containing, G protein-coupled receptors (LGRs) with at least seven members in mammals. Based on the sequences of mammalian glycoprotein hormone receptors, we have identified a new LGR in Drosophila melanogaster and named it as fly LGR2 to distinguish it from the previously reported fly LH/FSH/TSH receptor (renamed as fly LGR1). Genomic analysis indicated the presence of 10 exons in fly LGR2 as compared with 16 exons in fly LGR1. The deduced fly LGR2 complementary DNA (cDNA) showed 43 and 64% similarity to the fly LGR1 in the ectodomain and transmembrane region, respectively. Comparison of 12 LGRs from diverse species indicated that these proteins can be divided into three subfamilies and fly LGR1 and LGR2 belong to different subfamilies. Potential signaling mechanisms were tested in human 293T cells overexpressing the fly receptors. Of interest, fly LGR1, but not LGR2, showed constitutive activity as reflected by elevated basal cAMP production in transfected cells. The basal activity of fly LGR1 was further augmented following point mutations of key residues in the intracellular loop 3 or transmembrane VI, similar to those found in patients with familial male precocious puberty. The present study reports the cloning of fly LGR2 and indicates that the G protein-coupling mechanism is conserved in fly LGR1 as compared with the mammalian glycoprotein hormone receptors. The characterization of fly receptors with features similar to mammalian glycoprotein hormone receptors allows a better understanding of the evolution of this unique group of GPCRs and future elucidation of their ligand signaling mechanisms.
促黄体生成素（LH）、促卵泡生成素（FSH）和促甲状腺激素（TSH）的受体属于大型G蛋白偶联受体（GPCR）超家族，其独特之处在于具有一个大的N端细胞外（胞外）结构域，该结构域对于与大型糖蛋白激素配体的相互作用很重要。最近的研究表明，富含亮氨酸重复序列的G蛋白偶联受体（LGR）大家族在进化，在哺乳动物中至少有七个成员。基于哺乳动物糖蛋白激素受体的序列，我们在黑腹果蝇中鉴定出一种新的LGR，并将其命名为果蝇LGR2，以区别于先前报道的果蝇LH/FSH/TSH受体（重新命名为果蝇LGR1）。基因组分析表明，果蝇LGR2有10个外显子，而果蝇LGR1有16个外显子。推导的果蝇LGR2互补DNA（cDNA）在外显结构域和跨膜区域分别与果蝇LGR1有43%和64%的相似性。对来自不同物种的12种LGR的比较表明，这些蛋白质可分为三个亚家族，果蝇LGR1和LGR2属于不同的亚家族。在过表达果蝇受体的人293T细胞中测试了潜在的信号传导机制。有趣的是，果蝇LGR1而非LGR2表现出组成性活性，这在转染细胞中基础cAMP产生升高中得到体现。果蝇LGR1的基础活性在细胞内环3或跨膜VI中的关键残基发生点突变后进一步增强，类似于在家族性男性性早熟患者中发现的情况。本研究报道了果蝇LGR2的克隆，并表明与哺乳动物糖蛋白激素受体相比，果蝇LGR1中的G蛋白偶联机制是保守的。对具有与哺乳动物糖蛋白激素受体相似特征的果蝇受体的表征，有助于更好地理解这一独特的GPCR组的进化，并为未来阐明其配体信号传导机制提供帮助。
