Byambaragchaa Munkhzaya, Kang Han-Ju, Park Sei Hyen, Shin Min Gyu, Won Kyong-Mi, Kang Myung-Hwa, Min Kwan-Sik
Carbon-Neutral Resources Research Center, Anseong 17579, Republic of Korea.
Genetic Engineering, Hankyong National University, Anseong 17579, Republic of Korea.
Curr Issues Mol Biol. 2025 Jul 25;47(8):590. doi: 10.3390/cimb47080590.
Equine lutropin hormone/choriogonadotropin receptor (LH/CGR) is a G protein-coupled receptor that binds to both luteinizing hormone and choriogonadotropin, with multiple potential N-linked glycosylation sites in the long extracellular domain region. The roles of these glycosylation sites in hormone binding have been widely studied; however, their relationships with cyclic adenosine monophosphate (cAMP) activation, loss of cell surface receptors, and phosphorylated extracellular signal-regulated kinases1/2 (pERK1/2) expression are unknown. We used site-directed mutagenesis with the substitution of Asn for Gln to alter the consensus sequences for N-linked glycosylation, and cAMP signaling was analyzed in the mutants. Specifically, the N174Q and N195Q mutants exhibited markedly reduced expression levels, reaching approximately 15.3% and 2.5%, respectively, of that observed for wild-type equine LH/CGR. Correspondingly, the cAMP EC values were decreased by 7.6-fold and 5.6-fold, respectively. Notably, the N195Q mutant displayed an almost complete loss of cAMP activity, even at high concentrations of recombinant eCG, suggesting a critical role for this glycosylation site in receptor function. Despite these alterations, Western blot analysis revealed that pERK1/2 phosphorylation peaked at 5 min following agonist stimulation across all mutants, indicating that the ERK1/2 signaling pathway remains functionally intact. This study demonstrates that the specific N-linked glycosylation site, N195, in equine LH/CGR is indispensable for cAMP activity but is normally processed in pERK1/2 signaling. Thus, we suggest that in equine LH/CGR, agonist treatment induces biased signaling, differentially activating cAMP signaling and the pERK1/2 pathway.
马促黄体素激素/绒毛膜促性腺激素受体(LH/CGR)是一种G蛋白偶联受体,可与促黄体生成素和绒毛膜促性腺激素结合,在长细胞外结构域区域有多个潜在的N-连接糖基化位点。这些糖基化位点在激素结合中的作用已得到广泛研究;然而,它们与环磷酸腺苷(cAMP)激活、细胞表面受体丢失以及细胞外信号调节激酶1/2(pERK1/2)磷酸化表达之间的关系尚不清楚。我们使用定点诱变将天冬酰胺替换为谷氨酰胺,以改变N-连接糖基化的共有序列,并对突变体中的cAMP信号进行了分析。具体而言,N174Q和N195Q突变体的表达水平显著降低,分别达到野生型马LH/CGR观察值的约15.3%和2.5%。相应地,cAMP的半数有效浓度分别降低了7.6倍和5.6倍。值得注意的是,即使在高浓度重组eCG的情况下,N195Q突变体的cAMP活性几乎完全丧失,这表明该糖基化位点在受体功能中起关键作用。尽管有这些改变,但蛋白质免疫印迹分析显示,在所有突变体中,激动剂刺激后5分钟pERK1/2磷酸化达到峰值,这表明ERK1/2信号通路在功能上仍然完整。本研究表明,马LH/CGR中特定的N-连接糖基化位点N195对于cAMP活性是不可或缺的,但在pERK1/2信号传导中通常是正常处理的。因此,我们认为在马LH/CGR中,激动剂治疗会诱导偏向性信号传导,差异激活cAMP信号传导和pERK1/2途径。