Avenir, INSERM U889, Université Victor Segalen Bordeaux 2, F-33076 Bordeaux, France.
Semin Cell Dev Biol. 2010 Jul;21(5):486-90. doi: 10.1016/j.semcdb.2009.12.005. Epub 2010 Jan 6.
Calnexin is an abundant integral membrane phosphoprotein of the endoplasmic reticulum (ER) of eukaryotic cells. The role of the luminal domain as an N-glycoprotein specific lectin has been well-established. Cytosolic C-terminal domain phosphorylation of calnexin has recently been elucidated in glycoprotein folding and quality control. Signalling of the presence of unfolded proteins from the lumen of the ER is mediated by the three ER membrane sensor proteins Ire1, ATF6 and PERK. The observation that the C-terminus of calnexin is differentially phosphorylated when glycoproteins are misfolded initiated our search for functional roles of calnexin phosphorylation. Recent studies have defined a role for phosphorylation at a proline-directed kinase site (Ser563) in ER protein quality control, while phosphorylation at a casein kinase 2 site (Ser534, Ser544) may be linked to transport functions. There are also four other abundant integral membrane phosphoproteins in the ER, and these may be components of other signalling pathways that link and coordinate other ER functions with the rest of the cell.
钙连蛋白是真核细胞内质网（ER）中丰富的完整膜磷蛋白。其腔域作为 N-糖蛋白特异性凝集素的作用已得到充分证实。最近在糖蛋白折叠和质量控制中阐明了钙连蛋白胞质 C 末端结构域磷酸化的作用。内质网腔中未折叠蛋白的存在信号是通过三种内质网膜传感器蛋白 Ire1、ATF6 和 PERK 介导的。当糖蛋白错误折叠时，钙连蛋白 C 末端会发生差异磷酸化，这促使我们寻找钙连蛋白磷酸化的功能作用。最近的研究定义了在 ER 蛋白质量控制中，一个脯氨酸定向激酶位点（Ser563）磷酸化的作用，而酪蛋白激酶 2 位点（Ser534、Ser544）的磷酸化可能与运输功能有关。内质网中还有另外四种丰富的完整膜磷蛋白，它们可能是其他信号通路的组成部分，这些信号通路将 ER 的其他功能与细胞的其他部分联系和协调起来。
