α-Lactalbumin is unfolded by all classes of surfactants but by different mechanisms
α-Lactalbumin is unfolded by all classes of surfactants but by different mechanisms
复制标题
DOI：
10.1016/j.jcis.2008.10.021
复制
发表时间：
2009-01-15
影响因子：
9.9
通讯作者：
Westh, Peter
中科院分区：
文献类型：
--
作者：
Otzen, Daniel E.;Sehgal, Pankaj;Westh, Peter
我们证明所有四类表面活性剂（阴离子、阳离子、非离子和两性离子）都会使 α-乳清蛋白 (α LA) 变性，使 α LA 成为比较其变性机制的优秀模型系统。在所有表面活性剂中，这至少涉及两个步骤，但由于带电表面活性剂的强结合特性，这在带电表面活性剂中更为复杂。在非常低的浓度下，带电表面活性剂作为单体特异性结合，但只有当 4-10 个表面活性剂分子结合在蛋白质表面上形成簇时，才会发生第一次变性过程，随后当 20-25 个表面活性剂分子结合时，会发生第二次结构损失。亚胶束相互作用可以建模为多个位点的简单独立结合，在胶束形成开始之前不会达到饱和。相反，在两性离子和非离子表面活性剂存在的情况下，通过量热法没有检测到特定的亚胶束表面活性剂结合，并且变性仅发生在 cmc 周围。带电表面活性剂的展开速率非常快，并且在 cmc 周围达到类似的平台水平，表明单体和胶束在相互排斥的基础上起作用。相比之下，两性离子和非离子表面活性剂的解折叠过程缓慢。并且该速率随着 cmc 的增加而增加，表明单体与胶束协同变性。 (C) 2008 Elsevier Inc. 保留所有权利。
We show that all four classes of surfactants (anionic, cationic, non-ionic, and zwitterionic) denature alpha-lactalbumin (alpha LA), making alpha LA an excellent model system to compare their denaturation mechanisms. This involves at least two steps in all surfactants but is more complex in charged surfactants due to their strong binding properties. At very low concentrations, charged surfactants bind specifically as monomers, but the first denaturation process only sets in when 4-10 surfactant molecules are bound to form clusters on the protein surface and is followed by a second loss of structure as 20-25 surfactant molecules are bound. Sub-micellar interactions can be modeled as simple independent binding at multiple sites which does not achieve saturation before micelle formation sets in. In contrast, no specific sub-micellar surfactant binding is detected by calorimetry in the presence of zwitterionic and non-ionic surfactants, and denaturation only Occurs around the cmc. Unfolding rates are very rapid in charged surfactants and reach a similar plateau level around the cmc, indicating that monomers and micelles operate on a mutually exclusive basis. In contrast, unfolding occurs slowly in zwitterionic and non-ionic surfactants; and the rate increases with the cmc, suggesting that monomers cooperate with micelles in denaturation. (C) 2008 Elsevier Inc. All rights reserved.