Wang Shao-Chun, Lee C Ted
Department of Chemical Engineering and Material Science, University of Southern California, Los Angeles, California 90089-1211, USA.
J Phys Chem B. 2006 Aug 17;110(32):16117-23. doi: 10.1021/jp060981n.
The interaction of a light-responsive azobenzene surfactant with bovine serum albumin (BSA) has been investigated as a means to examine photoreversible changes in protein secondary structure. The cationic azobenzene surfactant undergoes a reversible photoisomeriztion upon exposure to the appropriate wavelength of light, with the visible-light (trans) form being more hydrophobic and, thus, inducing a greater degree of protein unfolding than the UV-light (cis) form. Fourier transform infrared (FT-IR) spectroscopy is used to provide quantitative information on the secondary structure elements in the protein (alpha-helices, beta-strands, beta-turns, and unordered domains). Comparing the secondary structure changes induced by light illumination in the presence of the photoresponsive surfactant with previous measurements of the tertiary structure of BSA obtained from small-angle neutron scattering (SANS) allows the three discrete conformation changes in BSA to be fully characterized. At low surfactant concentrations, an alpha-helix --> beta-structure rearrangement is observed as the tertiary structure of BSA changes from a heart-shaped to a distorted heart-shaped conformation. Intermediate surfactant concentrations lead to a dramatic decrease in the alpha-helix fraction in favor of unordered structures, which is accompanied by an unfolding of the C-terminal portion of the protein as evidenced from SANS. Further increases in photosurfactant concentration lead to a beta --> unordered transition with the protein adopting a highly elongated conformation in solution. Each of these protein conformational changes can be precisely and reversibly controlled with light illumination, as revealed through FT-IR spectra collected during repeated visible-light <--> UV-light cycles.
已对光响应性偶氮苯表面活性剂与牛血清白蛋白（BSA）之间的相互作用进行了研究，以此作为一种检测蛋白质二级结构光可逆变化的手段。阳离子偶氮苯表面活性剂在暴露于适当波长的光时会发生可逆的光异构化，可见光（反式）形式比紫外光（顺式）形式疏水性更强，因此能诱导更大程度的蛋白质解折叠。傅里叶变换红外（FT-IR）光谱用于提供有关蛋白质中二级结构元件（α-螺旋、β-链、β-转角和无规结构域）的定量信息。将在光响应性表面活性剂存在下光照诱导的二级结构变化与先前通过小角中子散射（SANS）获得的BSA三级结构测量结果进行比较，可以全面表征BSA中三种离散的构象变化。在低表面活性剂浓度下，随着BSA的三级结构从心形变为扭曲心形构象，会观察到α-螺旋向β-结构的重排。中等表面活性剂浓度会导致α-螺旋比例急剧下降，有利于形成无规结构，同时蛋白质的C端部分发生解折叠，这从SANS中可以得到证明。光表面活性剂浓度的进一步增加会导致β向无规转变，蛋白质在溶液中呈现高度伸长的构象。通过在重复的可见光<->紫外光循环过程中收集的FT-IR光谱表明，这些蛋白质构象变化中的每一种都可以通过光照精确且可逆地控制。
