MICROCALORIMETRIC STUDY OF WHEAT-GERM-AGGLUTININ BINDING TO N-ACETYLGLUCOSAMINE AND ITS OLIGOMERS
MICROCALORIMETRIC STUDY OF WHEAT-GERM-AGGLUTININ BINDING TO N-ACETYLGLUCOSAMINE AND ITS OLIGOMERS
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DOI：
10.1021/bi00165a012
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发表时间：
1992-12-22
期刊：
影响因子：
2.9
通讯作者：
FREIRE, E
中科院分区：
文献类型：
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作者：
BAINS, G;LEE, RT;FREIRE, E
用等温滴定量热法测定了麦胚凝集素（WGA）与N-乙酰氨基葡萄糖（GlcNAc）及其β（1，4）寡聚体的缔合能。在26 ℃下，用GlcNAc、（GlcNAc）2、（GlcNAc）3、（GlcNAc）4和（GlcNAc）5滴定WGA，获得的结合常数分别为0.4、5.3、11.1、12.3和19.1 mM-1，结合焓分别为-6.1、-15.6、-19.4、-19.3和-18.2 kcalmol-1。术语TDELTAS始终为负值，表明结合过程是由化学驱动的。在pH 4.5下进行的WGA滴定与在pH 7.0下进行的滴定无显著差异，表明pK（a）在此范围内的基团均不直接参与结合事件。此外，在具有较高质子化焓的缓冲系统中进行滴定没有改变结合焓，证实当WGA在pH 7下结合GlcNAc残基时没有净质子化或去质子化。四个独立的结合位点的模型被发现，充分描述的结合曲线，除了在（GlcNAc）4的情况下，表现出积极的协同性。在WGA-（GlcNAC）2复合物的结构的背景下讨论了能量值。
The energetics of association of wheat germ agglutinin (WGA) with N-acetylglucosamine (GlcNAc) and its beta(1,4) oligomers have been measured using isothermal titration calorimetry. Association constants of 0.4, 5.3, 11.1, 12.3, and 19.1 mM-1 and enthalpies of binding of -6.1, -15.6, -19.4, -19.3, and -18.2 kcal mol-1 were obtained at 26-degrees-C for the titration of WGA with GlcNAc, (GlcNAc)2, (GlcNAC)3, (GlcNAC)4, and (GlcNAc)5, respectively. The term TDELTAS was always of negative value, indicating that the binding process is enthalpically driven. Titrations of WGA performed at pH 4.5 did not differ significantly from those performed at pH 7.0, suggesting that no groups with a pK(a) in this range are directly involved in the binding event. Also, performing the titration in a buffer system with a higher enthalpy of protonation did not change the enthalpy of binding confirming that there is no net protonation or deprotonation when WGA binds GlcNAc residues at pH 7. A model of four independent binding sites was found to adequately describe the binding curves, except in the case of (GlcNAc)4 which exhibited positive cooperativity. The energetic values are discussed within the context of the structure of the WGA-(GlcNAC)2 complex.