Otteken A, Moss B
Laboratory of Viral Diseases, NIAID, National Institutes of Health, Bethesda, Maryland 20892, USA.
J Biol Chem. 1996 Jan 5;271(1):97-103. doi: 10.1074/jbc.271.1.97.
The ubiquitous eukaryotic protein calreticulin has been detected in a wide variety of different cell types. Recently, calreticulin was found to bind in vitro to a number of proteins isolated from the endoplasmic reticulum. In addition, calreticulin has sequence similarities with the molecular chaperone calnexin. These data suggest that calreticulin might also act as a chaperone. We found that calreticulin associated transiently with a large number of newly synthesized cellular proteins. In cells expressing recombinant human immunodeficiency virus (HIV) envelope glycoprotein, gp160 bound transiently to calreticulin with a peak at 10 min after its synthesis. Binding of gp120 to calreticulin was not detected because proteolytic cleavage of gp160 occurs in the trans-Golgi. Nonglycosylated HIV envelope protein was not associated with calreticulin, suggesting a requirement for N-linked oligosaccharides on newly synthesized proteins as has been reported for calnexin. The in vivo binding kinetics of calnexin and calreticulin to gp160 were very similar. Sequential immunoprecipitations provided evidence for the existence of ternary complexes of gp160, calreticulin, and calnexin. The data suggested that most of the gp160 associated with calreticulin was also bound to calnexin but that only a portion of the gp160 associated with calnexin was also bound to calreticulin.
普遍存在的真核蛋白钙网蛋白已在多种不同细胞类型中被检测到。最近，发现钙网蛋白在体外可与从内质网分离出的多种蛋白质结合。此外，钙网蛋白与分子伴侣钙连蛋白具有序列相似性。这些数据表明钙网蛋白可能也充当伴侣蛋白。我们发现钙网蛋白与大量新合成的细胞蛋白短暂结合。在表达重组人免疫缺陷病毒（HIV）包膜糖蛋白的细胞中，gp160在合成后10分钟达到峰值时与钙网蛋白短暂结合。未检测到gp120与钙网蛋白的结合，因为gp160的蛋白水解切割发生在反式高尔基体中。非糖基化的HIV包膜蛋白不与钙网蛋白结合，这表明新合成的蛋白需要N-连接寡糖，这与钙连蛋白的情况一致。钙连蛋白和钙网蛋白与gp160在体内的结合动力学非常相似。连续免疫沉淀为gp160、钙网蛋白和钙连蛋白三元复合物的存在提供了证据。数据表明，与钙网蛋白结合的大多数gp160也与钙连蛋白结合，但与钙连蛋白结合的gp160中只有一部分也与钙网蛋白结合。
