Oregon National Primate Research Center, Beaverton, 97006, USA.
Cell Biochem Funct. 2010 Jan;28(1):66-73. doi: 10.1002/cbf.1622.
Retention of misfolded proteins by the endoplasmic reticulum (ER) is a quality control mechanism involving the participation of endogenous chaperones such as calnexin (CANX). CANX interacts with and restricts plasma membrane expression (PME) of the gonadotropin releasing hormone receptor (GnRHR), a G protein-coupled receptor. CANX also interacts with ERP-57 a thiol oxidoreductase chaperone present in the ER. CANX along with ERP-57 promotes the formation of disulfide bond bridges in nascent proteins. The human GnRH receptor (hGnRHR) is stabilized by two disulfide bond bridges (C(14)-C(200) and C(114)-C(196)), that, when broken, lead to a decrease in receptor expression at the plasma membrane. To determine if the presence of chaperones CANX and ERP-57 exerts an influence over membrane routing and second messenger activation, we assessed the effect of various mutants including those with broken disulfide bridges (Cys --> Ala) along with the hGnRHR. The effect of chaperones on mutants was insignificant, whereas the over expression of ERP-57 led to an hGnRHR retention. This effect was further enhanced by cotransfection with cDNA for CANX showing receptor retention by ERP-57 augmented by CANX, suggesting utilization of these chaperones for quality control of the GnRHR.
内质网（ER）中错误折叠蛋白的保留是一种质量控制机制，涉及到内源性伴侣蛋白如钙网蛋白（CANX）的参与。CANX 与促性腺激素释放激素受体（GnRHR）相互作用并限制其在质膜上的表达（PME），GnRHR 是一种 G 蛋白偶联受体。CANX 还与 ER 中存在的硫氧还蛋白伴侣 ERp57 相互作用。CANX 与 ERp57 一起促进新生蛋白中二硫键桥的形成。人类 GnRH 受体（hGnRHR）由两个二硫键桥（C(14)-C(200)和 C(114)-C(196))稳定，当这些桥断裂时，会导致质膜上受体表达减少。为了确定伴侣蛋白 CANX 和 ERp57 的存在是否对膜路由和第二信使激活有影响，我们评估了各种突变体的影响，包括那些二硫键断裂的突变体（Cys --> Ala）以及 hGnRHR。伴侣蛋白对突变体的影响并不显著，而 ERp57 的过表达导致 hGnRHR 的保留。当与 CANX 的 cDNA 共转染时，这种效应进一步增强，表明 ERp57 通过 CANX 增强了受体的保留，这表明这些伴侣蛋白被用于 GnRHR 的质量控制。
