Audette G F, Vandonselaar M, Delbaere L T
Department of Biochemistry, University of Saskatchewan, 107 Wiggins Road, Saskatoon, Saskatchewan, S7N 5E5, Canada.
J Mol Biol. 2000 Dec 1;304(3):423-33. doi: 10.1006/jmbi.2000.4214.
The tertiary and quaternary structure of the lectin I from Ulex europaeus (UE-I) has been determined to 2.2 A resolution. UE-I is a dimeric metalloglycoprotein that binds the H-type 2 human blood group determinant [alpha-L-Fucalpha(1-->2)-beta-D-Galbeta(1-->4)-beta-D-Glc NAcalpha-]. Nine changes from the published amino acid sequence were necessary to account for the electron density. The quaternary structural organization of UE-I is that of the most commonly occurring legume lectin dimer. The tertiary structure of the monomeric subunits is similar to that in the conventional lectin subunit; however, some structural differences are noted. These differences include a four-stranded anti-parallel "S" sheet in UE-I versus the five-stranded S sheet in other lectin monomers. The Ala residue of the Ala-Asp cis-peptide bond present in the carbohydrate-binding site of the conventional lectin monomer is replaced with a Thr in the UE-I structure. Also, a novel disulfide bridge linking Cys115 and Cys150 is present. There are two metallic ions, one calcium and the other manganese, per subunit. N-linked oligosaccharides are at residues 23 and 111 of each subunit. One molecule of R-2-methyl-2, 4-pentanediol (R-MPD) is present in a shallow depression on the surface of each subunit. In order to examine the binding of the H-type 2 blood group determinant by UE-I, its beta-methyl glycoside (H-type 2-OMe) was docked into the binding site of R-MPD. The epitope previously identified for H-type 2-OMe by chemical mapping proved, with only minor adjustment of amino acid residues, to be complementary to the shallow cavity occupied by R-MPD in the structure. Several key interactions have been proposed between the H-type 2-OMe and UE-I.
已确定来自欧洲荆豆的凝集素I（UE-I）的三级和四级结构，分辨率为2.2埃。UE-I是一种二聚体金属糖蛋白，可结合H型2人类血型决定簇[α-L-岩藻糖α(1→2)-β-D-半乳糖β(1→4)-β-D-葡萄糖胺α-]。为了与电子密度相符，已公布的氨基酸序列中有九个位置发生了变化。UE-I的四级结构组织是最常见的豆科植物凝集素二聚体结构。单体亚基的三级结构与传统凝集素亚基的结构相似；然而，也发现了一些结构差异。这些差异包括UE-I中为四链反平行“S”片层，而其他凝集素单体中为五链S片层。传统凝集素单体碳水化合物结合位点中存在的Ala-Asp顺式肽键的Ala残基在UE-I结构中被Thr取代。此外，还存在一个连接Cys115和Cys150的新型二硫键。每个亚基有两个金属离子，一个是钙，另一个是锰。N-连接寡糖位于每个亚基的第23和111位残基处。每个亚基表面的浅凹陷处存在一分子R-2-甲基-2,4-戊二醇（R-MPD）。为了研究UE-I与H型2血型决定簇的结合，将其β-甲基糖苷（H型2-OMe）对接至R-MPD的结合位点。通过化学图谱先前确定的H型2-OMe的表位，只需对氨基酸残基进行微小调整，就证明与结构中R-MPD占据的浅腔互补。已提出H型2-OMe与UE-I之间存在几种关键相互作用。
