Binding of the cellulose-binding domain of exoglucanase Cex from Cellulomonas fimi to insoluble microcrystalline cellulose is entropically driven
Binding of the cellulose-binding domain of exoglucanase Cex from Cellulomonas fimi to insoluble microcrystalline cellulose is entropically driven
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DOI：
10.1073/pnas.93.22.12229
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发表时间：
1996-10-29
影响因子：
11.1
通讯作者：
Haynes, CA
中科院分区：
文献类型：
--
作者：
Creagh, AL;Ong, E;Haynes, CA
结合等温滴定微量热法和溶液消耗等温线数据分析了纤维素结合域（CBD）与不溶性细菌微晶纤维素结合的热力学。对两种假定的结合模型的等温滴定微量热法数据的分析表明，细菌微晶纤维素表面存在两类独立的结合位点，其中主要的高亲和力位点的特征在于Langmuir型K-a为6.3（+/- 1.4）× 10（7）M（-1），低亲和力位点的K-a为1.1（+/- 0.6）× 10（6）M（-1）。CBDCex与任一位点的结合是放热的，但主要是由熵的大的正变化驱动的。这不同于蛋白质与可溶性碳水化合物的结合，其通常由相对大的放热标准结合焓变化驱动。微分热容量的变化是大的和负的，这表明吸附剂和蛋白质脱水效应作出了主导贡献的驱动力结合。
Isothermal titration microcalorimetry is combined with solution depletion isotherm data to analyze the thermodynamics of binding of the cellulose-binding domain (CBD) from the beta-1,4-(exo)glucanase Cex of Cellulomonas fimi to insoluble bacterial microcrystalline cellulose. Analysis of isothermal titration microcalorimetry data against two putative binding models indicates that the bacterial microcrystalline cellulose surface presents two independent classes of binding sites, with the predominant high-affinity site being characterized by a Langmuir-type K-a of 6.3 (+/- 1.4) x 10(7) M(-1) and the low-affinity site by a K-a of 1.1 (+/- 0.6) x 10(6) M(-1). CBDCex binding to either site is exothermic, but is mainly driven by a large positive change in entropy. This differs from protein binding to soluble carbohydrates, which is usually driven by a relatively large exothermic standard enthalpy change for binding. Differential heat capacity changes are large and negative, indicating that sorbent and protein dehydration effects make a dominant contribution to the driving force for binding.