Conformational flexibility of α-lactalbumin related to its membrane binding capacity
Conformational flexibility of α-lactalbumin related to its membrane binding capacity
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DOI：
10.1016/j.jmb.2005.04.020
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发表时间：
2005-06-24
影响因子：
5.6
通讯作者：
Martínez, A
中科院分区：
文献类型：
--
作者：
Halskau, O;Underhaug, J;Martínez, A
用荧光光谱、圆二色谱和核磁共振研究了阴离子表面活性剂十二烷基硫酸钠(十二烷基硫酸钠)诱导的牛乳蛋白(BLA)的不同折叠状态。测定了不含十二烷基硫酸钠的条件下蛋白质的溶液结构，表明在自然条件下仍具有流动性。微摩尔浓度的十二烷基硫酸钠使BLA部分变性为类熔球(MG)状态，从天然状态到类MG状态的转变依赖于pH，当pH为6.5时，蛋白质对表面活性剂更敏感。本征发射荧光的测量表明，与CD数据估计的大部分二级结构相比，在较低浓度的十二烷基硫酸钠时，三级结构消失。由低浓度的十二烷基硫酸钠诱导的类MG状态在核磁共振中观察不到，可能是波动和/或聚集。当较高浓度的十二烷基硫酸钠高于临界胶束浓度时，核磁共振可观察到的状态重新出现。这种胶束相关的构象被部分指定，并被发现与酸-三氟乙醇状态有很大的相似之处，保留了天然BLA的A和C螺旋的弱化版本。我们从蛋白质固有的灵活性以及它形成多折叠状态和与膜结合的能力方面讨论了结果。此外，我们还提出，具有稳定的类MG构象的蛋白质可以在体内通过低水平的具有表面活性的化合物来稳定这些状态。(C)2005爱思唯尔有限公司。保留所有权利。
Different folding states of the small, globular milk protein bovine alpha-lactalbumin (BLA) induced by the anionic surfactant sodium dodecyl-sulphate (SDS) have been examined by fluorescence spectroscopy, CD and NMR. The solution structure of the protein in the absence of SDS was also determined, indicating fluidity even under native conditions. BLA is partly denatured to a molten globule (MG)-like state by micromolar concentrations of SDS, and the transitions from native to MG-like state are dependent on pH, the protein being more sensitive to the surfactant at pH 6.5. As indicated by measurements of the intrinsic emission fluorescence, the tertiary structure disappears at lower concentrations of SDS than most of the secondary structure, as estimated from CD data. The MG-like state induced by low concentrations of SDS is not observable by NMR, and is probably fluctuating and/or aggregating. At higher concentrations of SDS above the critic concentration of micelles, an NMR-observable state reappears. This micelle-associated conformer was partially assigned, and found to bear strong resemblance to the acid-trifluoroethanol state, retaining weakened versions of the A and C helix of native BLA. We discuss the results in terms of the inherent flexibility of the protein, and its ability to form multiple folding states and to bind to membranes. Also, we propose that proteins with stable MG-like conformers can have these states stabilized by low levels of compounds with surfactant properties in vivo. (c) 2005 Elsevier Ltd. All rights reserved.