Naismith J H, Field R A
Centre for Biomolecular Sciences, University, St. Andrews, Scotland, United Kingdom.
J Biol Chem. 1996 Jan 12;271(2):972-6. doi: 10.1074/jbc.271.2.972.
Despite the fact that complex saccharides play an important role in many biological recognition processes, molecular level descriptions of protein-carbohydrate interactions are sparse. The legume lectin concanavalin A (con A), from Canavalia ensiformis, specifically recognizes the trimannoside core of many complex glycans. We have determined the crystal structure of a con A-trimannoside complex at 2.3-A resolution now describe the trimannoside interaction with conA. All three sugar residues are in well defined difference electron density. The 1,6-linked mannose residue is bound at the previously reported monosaccharide binding site; the other two sugars bind in an extended cleft formed by residues Tyr-12, Pro-13, Asn-14, Thr-15, and Asp-16. Hydrogen bonds are formed between the protein and all three sugar residues. In particular, the 1,3-linked mannose residue makes a strong hydrogen bond with the main chain of the protein. In addition, a water molecule, which is conserved in other con A structures, plays an important role in anchoring the reducing sugar unit to the protein. The complex is further stabilized by van der Waals interactions. The structure provides a rationale for the high affinity of con A for N-linked glycans.
尽管复合糖在许多生物识别过程中发挥着重要作用，但蛋白质与碳水化合物相互作用的分子水平描述却很稀少。来自刀豆的豆科凝集素伴刀豆球蛋白A（Con A）能特异性识别许多复合聚糖的三甘露糖核心。我们现已确定了Con A - 三甘露糖复合物的晶体结构，分辨率为2.3 Å，并描述了三甘露糖与Con A的相互作用。所有三个糖残基都具有明确的差分电子密度。1,6 - 连接的甘露糖残基结合在先前报道的单糖结合位点；另外两个糖结合在由酪氨酸 - 12、脯氨酸 - 13、天冬酰胺 - 14、苏氨酸 - 15和天冬氨酸 - 16残基形成的延伸裂隙中。蛋白质与所有三个糖残基之间形成了氢键。特别是，1,3 - 连接的甘露糖残基与蛋白质的主链形成了强氢键。此外，在其他Con A结构中保守的一个水分子在将还原糖单元锚定到蛋白质上起着重要作用。复合物通过范德华相互作用进一步稳定。该结构为Con A对N - 连接聚糖的高亲和力提供了理论依据。
