Asker N, Axelsson M A, Olofsson S O, Hansson G C
Department of Medical Biochemistry, Göteborg University, Medicinaregatan 9A, S-413 90 Gothenburg, Sweden.
Biochem J. 1998 Oct 15;335 ( Pt 2)(Pt 2):381-7. doi: 10.1042/bj3350381.
Biosynthetic studies on the human MUC5AC mucin were performed by immunoprecipitations with antisera recognizing only the non-O-glycosylated apomucin in the colon adenocarcinoma cell line LS 174T. Pulse-chase studies and subcellular fractionations showed that MUC5AC formed dimers in the rough endoplasmic reticulum within 15 min of the initiation of biosynthesis. No non-O-glycosylated species larger than dimers were identified. The dimerization was N-glycosylation-dependent, because tunicamycin treatment significantly lowered the rate of dimerization. When the biosynthesis of MUC5AC apomucin was compared with that of MUC2 apomucin, also produced in the LS 174T cell line, both apomucins were assembled in similar ways with respect to their rates of dimerization with and without inhibition of N-glycosylation. No heterodimerization was observed between the human MUC5AC and the MUC2 apomucins despite the extensive sequence similarities in the positions of the cysteine residues in the C-termini proposed to be involved in mucin dimerization.
利用仅识别结肠腺癌细胞系LS 174T中未进行O-糖基化的脱辅基粘蛋白的抗血清，通过免疫沉淀法对人MUC5AC粘蛋白进行了生物合成研究。脉冲追踪研究和亚细胞分级分离表明，MUC5AC在生物合成开始后的15分钟内在粗面内质网中形成二聚体。未鉴定出大于二聚体的未进行O-糖基化的物种。二聚化依赖于N-糖基化，因为衣霉素处理显著降低了二聚化速率。当将MUC5AC脱辅基粘蛋白的生物合成与同样在LS 174T细胞系中产生的MUC2脱辅基粘蛋白的生物合成进行比较时，就二聚化速率而言，无论有无N-糖基化抑制，两种脱辅基粘蛋白的组装方式相似。尽管在拟参与粘蛋白二聚化的C末端半胱氨酸残基位置存在广泛的序列相似性，但未观察到人MUC5AC和MUC2脱辅基粘蛋白之间的异源二聚化。
