PRIMARY STRUCTURE AND TOPOLOGY OF BETA 1-4 GALATOSYLTRANSFERASE

β1-4半乳糖基转移酶一级结构的研究 (1-4半转移酶)在这一年继续存在。以推导出 1-4半乳糖基转移酶全氨基酸序列，基因组克隆 都是孤立的。NH2-末端序列来自于该cDNA和 基因组克隆表明合成了1-4半乳糖基转移酶 作为一个更大的前兆。缺少可溶和分泌的形式 大约72个残基-NHZ-末端多肽，包含 膜锚定结构域及其潜在的蛋白酶 易感序列-Arg-x-x-Arg-Arg-Leu-。牛奶酵素可以 是由较大的前体通过蛋白水解性切割产生的 在NHz信号锚和催化域之间。这个 高尔基体和细胞表面1-4半转移酶的拓扑结构可以 预测类似于一类膜蛋白，如 转铁蛋白受体，去唾液酸糖蛋白受体，β- 流感病毒半乳糖苷α-2，6-唾液酸基转移酶 唾液酸酶等，其具有NH2-末端“茎”结构 从跨膜双层的管腔侧延伸到 细胞质一侧。蛋白质结构的大部分，它携带 主要功能，面向管腔侧。

Studies on the primary structure of beta 1-4 galactosyltransferase (1-4 galtransferase) continued in this year. To deduce the complete amino acid sequence of 1-4 galtransferase, genomic clones were isolated. NH2-terminal end sequence derived from the cDNA and genomic clones showed that the 1-4 galtransferase is synthesized as a larger precursor. The soluble and secreted form is missing approximately 72-residue-NHz-terminal peptide which contains the membrane anchoring domain as well as the potential protease susceptible sequence - Arg-x-x-Arg-Arg-Leu-. The milk enzyme can be generated from the larger precursor by proteolytic cleavage between the NHz-signal-anchor and the catalytic domain. The topology of the Golgi and cell surface 1-4 galtransferase can be predicted to be similar to a class of membrane proteins, like the transferrin receptor, the asialoglycoprotein receptor, the beta- galactoside alpha-2, 6-sialyltransferase, the influenza virus sialidase etc., which have an NH2-terminal "stem" structure extending from the luminal side of the transmembrane bilayer to the cytoplasmic side. The bulk of the protein structure, which carries the main function, faces the lumen side.