C-type lectin-like carbohydrate recognition of the hemolytic lectin CEL-III containing ricin-type β-trefoil folds
C-type lectin-like carbohydrate recognition of the hemolytic lectin CEL-III containing ricin-type β-trefoil folds
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DOI：
10.1074/jbc.m705604200
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发表时间：
2007-12-28
影响因子：
4.8
通讯作者：
Kusunoki, Masami
中科院分区：
文献类型：
--
作者：
Hatakeyama, Tomomitsu;Unno, Hideaki;Kusunoki, Masami
CEL-III是从海洋无脊椎动物Cucumaria echinata中分离的一种Ca 2+依赖性溶血凝集素。CEL-III/GalNAc和CEL-III/甲基α-半乳糖苷复合物的三维结构通过X-射线晶体学分析解决。在这些复合物中，发现5个碳水化合物分子与位于多肽N-末端2/3部分的两个碳水化合物结合结构域（结构域1和2）结合，并且含有类似于蓖麻毒素B-链的β-三叶折叠。结合的碳水化合物分子的3-OH和4-OH与位于亚结构域1 α、1 γ、2 α、2 β和2 γ的Ca 2+配位，同时与附近的氨基酸侧链形成氢键网络，这类似于C型凝集素中的碳水化合物结合。碳水化合物的结合进一步稳定的芳香族氨基酸残基，如酪氨酸和色氨酸，通过堆积相互作用与碳水化合物的疏水面。突变分析证实了碳水化合物结合位点中氨基酸残基的重要性。结合的GalNAc和甲基α-半乳糖苷的取向类似于乳糖的半乳糖部分结合到蓖麻毒蛋白B链的碳水化合物结合位点，尽管蓖麻毒蛋白B链不需要Ca 2+离子用于碳水化合物结合。碳水化合物的结合诱导了亚结构域2 α和2 β中碳水化合物结合位点的局部结构变化。GalNAc的结合也引起结构域3的主链结构的轻微变化，这可能与特定碳水化合物结合后引起蛋白质寡聚化的构象变化有关。
CEL-III is a Ca2+ dependent hemolytic lectin, isolated from the marine invertebrate Cucumaria echinata. The three-dimensional structure of CEL-III/GalNAc and CEL-III/ methyl alpha-galactoside complexes was solved by x-ray crystallographic analysis. In these complexes, five carbohydrate molecules were found to be bound to two carbohydrate-binding domains (domains 1 and 2) located in the N-terminal 2/3 portion of the polypeptide and that contained beta-trefoil folds similar to ricin B-chain. The 3-OH and 4-OH of bound carbohydrate molecules were coordinated with Ca2+ located at the subdomains 1 alpha, 1 gamma, 2 alpha, 2 beta, and 2 gamma, simultaneously forming hydrogen bond networks with nearby amino acid side chains, which is similar to carbohydrate binding in C-type lectins. The binding of carbohydrates was further stabilized by aromatic amino acid residues, such as tyrosine and tryptophan, through a stacking interaction with the hydrophobic face of carbohydrates. The importance of amino acid residues in the carbohydrate-binding sites was confirmed by the mutational analyses. The orientation of bound GalNAc and methyl alpha-galactoside was similar to the galactose moiety of lactose bound to the carbohydrate-binding site of the ricin B-chain, although the ricin B-chain does not require Ca2+ ions for carbohydrate binding. The binding of the carbohydrates induced local structural changes in carbohydrate-binding sites in subdomains 2 alpha and 2 beta. Binding of GalNAc also induced a slight change in the main chain structure of domain 3, which could be related to the conformational change upon binding of specific carbohydrates to induce oligomerization of the protein.