Binding of multivalent carbohydrates to concanavalin A and Dioclea grandiflora lectin -: Thermodynamic analysis of the "multivalency effect"
Binding of multivalent carbohydrates to concanavalin A and Dioclea grandiflora lectin -: Thermodynamic analysis of the "multivalency effect"
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DOI：
10.1074/jbc.275.19.14223
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发表时间：
2000-05-12
影响因子：
4.8
通讯作者：
Brewer, CF
中科院分区：
文献类型：
--
作者：
Dam, TK;Roy, R;Brewer, CF
用等温滴定微量热法研究了一系列合成的多价碳水化合物类似物与Man/ glc特异性凝集素刀豆蛋白a和大花菜凝集素的结合。选择具有末端α -d -甘露诺吡喃苷残基的二聚体类似物和具有末端3,6-二- o -（α -d -甘露诺吡喃糖基）- α -d -甘露诺吡喃苷残基的二聚体、三聚体和四聚体类似物，分别比较低亲和力和高亲和力类似物的效果。在等温滴定微量热实验中，发现了阻止碳水化合物-凝集素交联配合物沉淀的实验条件。结果表明，凝集素每个单体上的结合位点数目n的值与每个碳水化合物的结合表位数目（价）成反比。因此，观察到单价糖、二价糖和四价糖分别与两种凝集素结合的n值分别接近1.0、0.50和0.25。重要的是，观察到魔芋蛋白a和桔梗凝集素的三链类似物的功能价存在差异。在高亲和力类似物中，结合焓H与结合表位的数目成正比。例如，四价三甲苷类似物的H几乎是相应的单价类似物的四倍。多价碳水化合物相对于单价类似物的K-a值的增加，被称为“多价效应”，被证明是由于更多的正熵（T δ S）对前糖结合的贡献。给出了区分多价配体与具有多个相等亚位的单个受体结合与与单独受体分子结合的一般热力学模型。
Binding of a series of synthetic multivalent carbohydrate analogs to the Man/Glc-specific lectins concanavalin A and Dioclea grandiflora lectin was investigated by isothermal titration microcalorimetry. Dimeric analogs possessing terminal alpha-D-mannopyranoside residues, and di-, tri-, and tetrameric analogs possessing terminal 3,6-di-O-(alpha-D-mannopyranosyl)-alpha-D-mannopyranoside residues, which is the core trimannoside of asparagine-linked carbohydrates, were selected in order to compare the effects of low and high affinity analogs, respectively. Experimental conditions were found that prevented precipitation of the carbohydrate-lectin cross-linked complexes during the isothermal titration microcalorimetry experiments. The results show that the value of n, the number of binding sites on each monomer of the lectins, is inversely proportional to the number of binding epitopes (valency) of each carbohydrate. Hence, n values close to 1.0, 0.50, and 0.25 were observed for the binding of mono-, di-, and tetravalent sugars, respectively, to the two lectins, Importantly, differences in the functional valency of a triantennary analog for concanavalin A and D. grandiflora lectin are observed. The enthalpy of binding, Delta H, is observed to be directly proportional to the number of binding epitopes in the higher affinity analogs. For example, Delta H of a tetravalent trimannoside analog is nearly four times greater than that of the corresponding monovalent analog. Increases in K-a values of the multivalent carbohydrates relative to monovalent analogs, known as the "multivalency effect," are shown to be due to more positive entropy (T Delta S) contributions to binding of the former sugars, A general thermodynamic model for distinguishing binding of multivalent ligands to a single receptor with multiple, equal subsites versus binding to separate receptor molecules is given.