PRIMARY STRUCTURE AND TOPOLOGY OF BETA 1-4 GALATOSYLTRANSFERASE

β 1-4半乳糖基转移酶一级结构的研究 (1-4今年继续进行。 推导 1-4半乳糖转移酶的完整氨基酸序列，基因组克隆 中分离出 来源于cDNA的NH 2-末端序列， 基因组克隆显示1-4半乳糖转移酶是合成的， 作为一个更大的先驱。 可溶性和分泌性形式缺失 大约72个残基-NHz-末端肽，其含有 膜锚定结构域以及潜在的蛋白酶 易感序列Arg-x-x-Arg-Arg-Leu-。 牛奶酶可以 通过蛋白水解裂解从较大的前体产生 在NHZ-信号-锚和催化结构域之间。 的 高尔基体和细胞表面1-4半乳糖转移酶的拓扑结构可以是 预测类似于一类膜蛋白，如 转铁蛋白受体，脱唾液酸糖蛋白受体，β- 半乳糖苷α-2，6-唾液酸转移酶，流感病毒 唾液酸酶等，其具有NH 2末端“茎”结构， 从跨膜双层的腔侧延伸到 胞质侧 蛋白质结构的主体， 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.