Navratil Amy M, Farmerie Todd A, Bogerd Jan, Nett Terry M, Clay Colin M
Department of Biomedical Sciences, Animal Reproduction and Biotechnology Laboratory, Colorado State University, Fort Collins, Colorado 80523, USA.
Biol Reprod. 2006 May;74(5):788-97. doi: 10.1095/biolreprod.105.048157. Epub 2005 Dec 21.
The mammalian type I GNRH receptor (GNRHR) is unique among G protein-coupled receptors (GPCRs) because of the absence of an intracellular C-terminus. Previously, we have found that the murine GNRHR is constitutively localized to low-density membrane microdomains termed lipid rafts. As such, association of the GNRHR with lipid rafts may reflect both a loss (C-terminus) and a gain (raft association address) of structural characteristics. To address this, we fused either the full-length C-terminus from the nonraft-associated LH receptor (LHCGR; GNRHR-LF) or a truncated (t631) LHCGR C-terminus to the GNRHR. These chimeric receptors are trafficked to the plasma membrane, bind ligand, and display increased agonist-induced receptor internalization, but they do not partition into lipid rafts. Thus, a heterologous C-terminus from a nonraft-associated GPCR redirects localization of the GNRHR to nonraft domains. In contrast to the murine GNRHR, the catfish GNRHR (cfGNRHR) possesses an intracellular C-terminus. We found that the cfGNRHR was localized to lipid rafts and that the cfGNRHR C-terminus did not alter raft localization of the mammalian receptor. Consistent with placement in different lipid microenvironments within the plasma membrane, fluorescence recovery after photobleaching revealed different lateral diffusion phenotypes of the raft-associated GNRHR and cfGNRHR versus the nonraft-associated GNRHR-LF fusion protein. We conclude that whereas an intracellular C-terminus is capable of redirecting the GNRHR to nonraft compartments, this is not a generalized feature of GPCR C-terminal tails. Thus, constitutive raft localization of the GNRHR is not simply a result of the loss of an intracellular C-terminus.
哺乳动物I型促性腺激素释放激素受体（GNRHR）在G蛋白偶联受体（GPCR）中独具特色，因为它没有细胞内C末端。此前，我们发现小鼠GNRHR组成性地定位于称为脂筏的低密度膜微区。因此，GNRHR与脂筏的结合可能既反映了结构特征的缺失（C末端），也反映了结构特征的获得（脂筏结合位点）。为了探究这一点，我们将非脂筏相关的促黄体生成素受体（LHCGR；GNRHR-LF）的全长C末端或截短的（t631）LHCGR C末端与GNRHR融合。这些嵌合受体被转运到质膜，结合配体，并表现出激动剂诱导的受体内化增加，但它们不会分配到脂筏中。因此，来自非脂筏相关GPCR的异源C末端将GNRHR的定位重定向到非脂筏区域。与小鼠GNRHR不同，鲶鱼GNRHR（cfGNRHR）具有细胞内C末端。我们发现cfGNRHR定位于脂筏，并且cfGNRHR C末端不会改变哺乳动物受体的脂筏定位。与置于质膜内不同的脂质微环境一致，光漂白后的荧光恢复显示，与非脂筏相关的GNRHR-LF融合蛋白相比，脂筏相关的GNRHR和cfGNRHR具有不同的侧向扩散表型。我们得出结论，虽然细胞内C末端能够将GNRHR重定向到非脂筏区室，但这不是GPCR C末端尾巴的普遍特征。因此，GNRHR的组成性脂筏定位不仅仅是细胞内C末端缺失的结果。
