Thingstad T, Vos H L, Hilkens J
Division of Tumor Biology, The Netherlands Cancer Institute, Plesmanlaan 121, 1066 CX Amsterdam, The Netherlands.
Biochem J. 2001 Jan 1;353(Pt 1):33-40.
Epiglycanin is a mucin-type glycoprotein present at the surface of TA3Ha mouse mammary tumour cells. It is a long rod-like glycoprotein with a molecular mass of 500 kDa. Its function has not yet been established but its overexpression can affect cell-cell and cell-matrix adhesion. To understand better the biological function of epiglycanin, we have studied the biochemical structure and biosynthesis of epiglycanin in TA3Ha cells. Pulse-chase labelling experiments with [(3)H]threonine revealed an early precursor with a molecular mass of approx. 300 kDa containing approx. 5-10 kDa of N-linked glycans. The precursor was gradually converted into a high-molecular-mass mature form, owing mainly, if not entirely, to O-glycosylation. The mature molecule consists of two major glycoforms that differ in sialylation. Unlike secreted mucins, epiglycanin did not form cysteine-bound multimers, providing further evidence that epiglycanin belongs to the class of membrane-associated mucins. The mature form, but not the precursor form, is shed from the cell surface. The half-life of epiglycanin on the cell surface was found to be approx. 60 h. These results provide the first detailed analysis of the biochemical structure and biosynthesis of epiglycanin.
Epiglycanin是一种存在于TA3Ha小鼠乳腺肿瘤细胞表面的粘蛋白型糖蛋白。它是一种分子量为500 kDa的长杆状糖蛋白。其功能尚未明确，但它的过表达会影响细胞间和细胞与基质的黏附。为了更好地理解Epiglycanin的生物学功能，我们研究了TA3Ha细胞中Epiglycanin的生化结构和生物合成。用[³H]苏氨酸进行脉冲追踪标记实验显示，有一个分子量约为300 kDa的早期前体，其含有约5 - 10 kDa的N - 连接聚糖。该前体逐渐转化为高分子量的成熟形式，这主要（如果不是完全）归因于O - 糖基化。成熟分子由两种主要的糖型组成，它们在唾液酸化方面存在差异。与分泌型粘蛋白不同，Epiglycanin不会形成半胱氨酸连接的多聚体，这进一步证明Epiglycanin属于膜相关粘蛋白类别。成熟形式而非前体形式会从细胞表面脱落。发现Epiglycanin在细胞表面的半衰期约为60小时。这些结果首次对Epiglycanin的生化结构和生物合成进行了详细分析。
