Loris R, Hamelryck T, Bouckaert J, Wyns L
Laboratorium voor Ultrastruktuur, Vlaams Interuniversitair Instituut voor Biotechnologie, Vrije Universiteit Brussel, Sint-Genesius-Rode, Belgium.
Biochim Biophys Acta. 1998 Mar 3;1383(1):9-36. doi: 10.1016/s0167-4838(97)00182-9.
The legume lectins are a large family of homologous carbohydrate binding proteins that are found mainly in the seeds of most legume plants. Despite their strong similarity on the level of their amino acid sequences and tertiary structures, their carbohydrate specificities and quaternary structures vary widely. In this review we will focus on the structural features of legume lectins and their complexes with carbohydrates. These will be discussed in the light of recent mutagenesis results when appropriate. Monosaccharide specificity seems to be achieved by the use of a conserved core of residues that hydrogen bond to the sugar, and a variable loop that determines the exact shape of the monosaccharide binding site. The higher affinity for particular oligosaccharides and monosaccharides containing a hydrophobic aglycon results mainly from a few distinct subsites next to the monosaccharide binding site. These subsites consist of a small number of variable residues and are found in both the mannose and galactose specificity groups. The quaternary structures of these proteins form the basis of a higher level of specificity, where the spacing between individual epitopes of multivalent carbohydrates becomes important. This results in homogeneous cross-linked lattices even in mixed precipitation systems, and is of relevance for their effects on the biological activities of cells such as mitogenic responses. Quaternary structure is also thought to play an important role in the high affinity interaction between some legume lectins and adenine and a series of adenine-derived plant hormones. The molecular basis of the variation in quaternary structure in this group of proteins is poorly understood.
豆类凝集素是一大类同源的碳水化合物结合蛋白，主要存在于大多数豆类植物的种子中。尽管它们在氨基酸序列和三级结构水平上有很强的相似性，但它们的碳水化合物特异性和四级结构却有很大差异。在这篇综述中，我们将重点关注豆类凝集素的结构特征及其与碳水化合物的复合物。在适当的时候，我们将根据最近的诱变结果进行讨论。单糖特异性似乎是通过使用与糖形成氢键的保守残基核心以及决定单糖结合位点确切形状的可变环来实现的。对含有疏水糖苷配基的特定寡糖和单糖的较高亲和力主要源于单糖结合位点旁边的一些不同亚位点。这些亚位点由少数可变残基组成，在甘露糖和半乳糖特异性组中均有发现。这些蛋白质的四级结构构成了更高水平特异性的基础，其中多价碳水化合物各个表位之间的间距变得很重要。这甚至在混合沉淀系统中也会导致均匀的交联晶格，并且与其对细胞生物活性（如促有丝分裂反应）的影响相关。四级结构也被认为在一些豆类凝集素与腺嘌呤以及一系列腺嘌呤衍生的植物激素之间的高亲和力相互作用中起重要作用。人们对这组蛋白质中四级结构变化的分子基础了解甚少。
