Hebert D N, Foellmer B, Helenius A
Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06520-8002, USA.
EMBO J. 1996 Jun 17;15(12):2961-8.
Calnexin (CNX) and calreticulin (CRT) are molecular chaperones that bind preferentially to monoglucosylated trimming intermediates of glycoproteins in the endoplasmic reticulum. To determine their role in the maturation of newly synthesized glycoproteins, we analyzed the folding and trimerization of in vitro translated influenza hemagglutinin (HA) in canine pancreas microsomes under conditions in which HA's interactions with CNX and CRT could be manipulated. While CNX bound to all folding intermediates (IT1, IT2 and NT), CRT was found to associate preferentially with the earliest oxidative form (IT1). If HA's binding to CNX and CRT was inhibited using a glucosidase inhibitor, castanospermine (CST), the rate of disulfide formation and oligomerization was doubled but the overall efficiency of maturation of HA decreased due to aggregation and degradation. If, on the other hand, HA was arrested in CNX-CRT complexes, folding and trimerization were inhibited. This suggested that the action of CNX and CRT, like that of other chaperones, depended on an 'on-and-off' cycle. Taken together, these results indicated that CNX and CRT promote correct folding by inhibiting aggregation, preventing premature oxidation and oligomerization, and by suppressing degradation of incompletely folded glycopolypeptides.
钙连蛋白（CNX）和钙网蛋白（CRT）是分子伴侣，它们在内质网中优先结合糖蛋白的单葡萄糖基化修剪中间体。为了确定它们在新合成糖蛋白成熟过程中的作用，我们分析了在可操纵HA与CNX和CRT相互作用的条件下，体外翻译的流感血凝素（HA）在犬胰腺微粒体中的折叠和三聚化情况。虽然CNX与所有折叠中间体（IT1、IT2和NT）结合，但发现CRT优先与最早的氧化形式（IT1）结合。如果使用葡糖苷酶抑制剂栗精胺（CST）抑制HA与CNX和CRT的结合，二硫键形成和寡聚化的速率会加倍，但由于聚集和降解，HA成熟的总体效率会降低。另一方面，如果HA被困在CNX-CRT复合物中，折叠和三聚化会受到抑制。这表明CNX和CRT的作用与其他分子伴侣一样，依赖于“开启和关闭”循环。综上所述，这些结果表明CNX和CRT通过抑制聚集、防止过早氧化和寡聚化以及抑制未完全折叠的糖多肽的降解来促进正确折叠。
