Cooper D N, Boulianne R P, Charlton S, Farrell E M, Sucher A, Lu B C
Departments of Anatomy and Psychiatry, Langley Porter Psychiatric Institute, Center for Neurobiology and Psychiatry, University of California, San Francisco, California 94143-0984, USA.
J Biol Chem. 1997 Jan 17;272(3):1514-21. doi: 10.1074/jbc.272.3.1514.
Galectins are members of a genetically related family of beta-galactoside-binding lectins. At least eight distinct mammalian galectins have been identified. More distantly related, but still conserving amino acid residues critical for carbohydrate-binding, are galectins in chicken, eel, frog, nematode, and sponge. Here we report that galectins are also expressed in a species of fungus, the inky cap mushroom, Coprinus cinereus. Two dimeric galectins are expressed during fruiting body formation which are 83% identical to each other in amino acid sequence and conserve all key residues shared by members of the galectin family. Unlike most galectins, these have no N-terminal post-translational modification and no cysteine residues. We expressed one of these as a recombinant protein and studied its carbohydrate-binding specificity using a novel nonradioactive assay. Binding specificity has been well studied for a number of other galectins, and like many of these, the recombinant C. cinereus galectin shows particular affinity for blood group A structures. These results demonstrate not only that the galectin gene family is evolutionarily much older than previously realized but also that fine specificity for complex saccharide structures has been conserved. Such conservation implies that galectins evolved to perform very basic cellular functions, presumably by interaction with glycoconjugates bearing complex lactoside carbohydrates resembling blood group A.
半乳糖凝集素是一个与β-半乳糖苷结合凝集素基因相关的家族成员。已鉴定出至少八种不同的哺乳动物半乳糖凝集素。在鸡、鳗鱼、青蛙、线虫和海绵中也存在半乳糖凝集素，它们的亲缘关系较远，但仍保留对碳水化合物结合至关重要的氨基酸残基。在此我们报告，半乳糖凝集素也在一种真菌——墨汁鬼伞（Coprinus cinereus）中表达。在子实体形成过程中表达了两种二聚体半乳糖凝集素，它们的氨基酸序列彼此有83%的同一性，并且保留了半乳糖凝集素家族成员共有的所有关键残基。与大多数半乳糖凝集素不同，这些半乳糖凝集素没有N端翻译后修饰，也没有半胱氨酸残基。我们将其中一种作为重组蛋白表达，并使用一种新型非放射性测定法研究其碳水化合物结合特异性。对许多其他半乳糖凝集素的结合特异性已经进行了充分研究，与其中许多半乳糖凝集素一样，重组的灰盖鬼伞半乳糖凝集素对A血型结构表现出特别的亲和力。这些结果不仅表明半乳糖凝集素基因家族在进化上比以前认识到的要古老得多，而且表明对复杂糖结构的精细特异性得到了保留。这种保留意味着半乳糖凝集素进化来执行非常基本的细胞功能，大概是通过与带有类似于A血型的复杂乳糖碳水化合物的糖缀合物相互作用来实现的。
