Structure and function of vertebrate beta-galactoside-binding lecitins

脊椎动物的金属非依赖性β-半乳糖苷结合凝集素被认为参与了胚胎发育和组织形态发生等多种重要的生物调节，其中复杂碳水化合物与其对应物之间的特异性相互作用起着至关重要的作用。它们还可能参与免疫系统的调节和恶性细胞的转移。本研究对鸡异凝素16 kDa的氨基酸全序列、核苷酸全序列、重组蛋白在大肠杆菌中的表达及胚胎发育过程中的去向进行了研究。这些结果为了解其在各种组织尤其是皮肤的形态发生中的作用，以及该凝集素家族的分子进化提供了可能。用重组人14 kDa凝集素的定点突变取代氨基酸残基的结果表明，被认为是最重要的色氨酸和一些半胱氨酸残基对碳水化合物的结合不是必需的。另一种人类凝集素29 kDa的cDNA是从乳腺癌文库中克隆的。测定了鳄鱼蛇毒中一种凝集素的氨基酸全序列，以确定其是否属于金属非依赖性凝集素家族。结果表明，蛇毒凝集素是钙依赖凝集素家族的一员。

Metal-independent beta-galactoside-binding lectins of vertebrates are considered to be involved a variety of important biological regulations such as development of embryo and morphogenesis of tissues in which specific interaction between complex carbohydrates and their counterparts play crucial roles. They are also suggested to be involved in regulation of immune system and metastasis of malignant cells. In the present research, complete amino acid sequence, complete nucleotide sequence of cDNA, expression of recombinant protein in E. coli and the fate during development of embryo of one of chicken isolectin, i. e., 16 kDa lectin, were elucidated. The results made it possible to understand its roles during morphogenesis of various tissues especially that of skin, and also molecular evolution of this lectin family. Effects of substitution of amino acid residues by site-directed mutagenesis of recombinant human 14 kDa lectin showed that a tryptophan and some cystein residues which had been considered to be mostly important were not essential for carbohydrate binding. A cDNA for another human lectin, 29 kDa lectin, was cloned from a library derived from a breast carcinoma. Complete amino acid sequence of a lectin contained in venom of Crotalus was determined in order to know whether it belongs to the metal-independent lectin family or not. The result clearly showed that the snake venom lectin is a member of calcium-dependent lectin family.