Saha Debasish, Ray Debes, Kohlbrecher Joachim, Aswal Vinod Kumar
Solid State Physics Division, Bhabha Atomic Research Centre, Mumbai 400 085, India.
Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institut, CH-5232 PSI Villigen, Switzerland.
ACS Omega. 2018 Jul 25;3(7):8260-8270. doi: 10.1021/acsomega.8b00630. eCollection 2018 Jul 31.
The interaction of protein and surfactant yields protein-surfactant complexes which have a wide range of applications in the cosmetics, foods, and pharmaceutical industries among others. Ionic and nonionic surfactants are known to interact differently with the protein. The interplay of electrostatic and hydrophobic interactions governs the resultant structure of protein-surfactant complexes. The present study enlightens the paramount role of the hydrophobic interaction, tuned by the hydrophobic tail length of ionic surfactants, in the unfolding of anionic bovine serum albumin (BSA) protein. The unfolding of BSA in the presence of four different tail-length cationic surfactants, that is, C10TAB, C12TAB, C14TAB, and C16TAB, has been investigated by small-angle neutron scattering and dynamic light scattering. All cationic surfactants unfold the protein at a certain concentration range. The propensity of protein unfolding increases with increasing the hydrophobic tail length. The denatured structure of BSA upon addition of cationic surfactants is characterized by the random flight model representing a beads-on-a-string chain-like complex. The unfolded protein binds the surfactant micelles in the protein-surfactant cluster. The micelles get elongated with the increasing concentration of cationic surfactants, whereas the number of micelles per cluster is decreased. In the final stage, the protein-surfactant cluster merges to one large micelle with unfolded protein wrapping the micelle surface. The pathway of protein unfolding is described in terms of the changes in the micellar size, the number of micelles formed per cluster, the separation between the micelles in the cluster, the aggregation number of micelles, and the number of proteins per cluster. The protein-surfactant interaction is further examined in the presence of a nonionic surfactant, that is, C12E10. The nonionic surfactant significantly suppresses the interaction of BSA protein with ionic surfactants by forming mixed micelles. As a result of the mixed micelles formation by ionic-nonionic surfactants, the ionic surfactant moves out from the unfolded BSA protein, and this enables the protein to refold back to its native structure. The propensity of mixed micelle-driven refolding of proteins is significantly changed with changing the tail length of the ionic surfactant.
蛋白质与表面活性剂的相互作用会产生蛋白质 - 表面活性剂复合物，这些复合物在化妆品、食品和制药等行业有着广泛的应用。已知离子型和非离子型表面活性剂与蛋白质的相互作用方式不同。静电相互作用和疏水相互作用的相互影响决定了蛋白质 - 表面活性剂复合物的最终结构。本研究揭示了由离子型表面活性剂的疏水尾链长度调节的疏水相互作用在阴离子牛血清白蛋白（BSA）蛋白质解折叠过程中的至关重要作用。通过小角中子散射和动态光散射研究了在四种不同尾链长度的阳离子表面活性剂（即C10TAB、C12TAB、C14TAB和C16TAB）存在下BSA的解折叠情况。所有阳离子表面活性剂在一定浓度范围内都会使蛋白质解折叠。蛋白质解折叠的倾向随着疏水尾链长度的增加而增大。加入阳离子表面活性剂后BSA的变性结构以随机飞行模型为特征，该模型代表一种串珠状链状复合物。解折叠的蛋白质在蛋白质 - 表面活性剂聚集体中与表面活性剂胶束结合。随着阳离子表面活性剂浓度的增加，胶束会伸长，而每个聚集体中的胶束数量会减少。在最后阶段，蛋白质 - 表面活性剂聚集体合并成一个大胶束，解折叠的蛋白质包裹着胶束表面。蛋白质解折叠的途径通过胶束大小的变化、每个聚集体中形成的胶束数量、聚集体中胶束之间的间距、胶束的聚集数以及每个聚集体中的蛋白质数量来描述。在非离子表面活性剂（即C12E10）存在的情况下，进一步研究了蛋白质 - 表面活性剂的相互作用。非离子表面活性剂通过形成混合胶束显著抑制了BSA蛋白质与离子型表面活性剂的相互作用。由于离子型 - 非离子型表面活性剂形成混合胶束，离子型表面活性剂从解折叠的BSA蛋白质中移出，这使得蛋白质能够重新折叠回其天然结构。随着离子型表面活性剂尾链长度的变化，混合胶束驱动蛋白质重新折叠的倾向会发生显著变化。
