Zhang Jing, Wang Shao-Chun, Lee C Ted
Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, 90089-1211, USA.
J Phys Chem B. 2009 Jun 25;113(25):8569-80. doi: 10.1021/jp807875u.
Photoreversible control of the conformation of bacteriorhodopsin in the presence of a light-responsive surfactant is demonstrated through combined UV-vis, FT-IR, and (31)P NMR spectroscopy and dynamic light scattering (DLS) measurements. The azobenzene-based surfactant photoisomerizes upon 434 nm visible (trans, relatively hydrophobic) and 350 nm UV (cis, relatively hydrophilic) illumination, allowing surfactant micellization to be reversibly controlled. This leads to partitioning of the membrane protein into micelles in the unfolded state under visible light, while UV light leads to solubilization of the protein within purple membrane bilayers in the folded state. A three-stage model of purple membrane-photosurfactant interactions is examined through NMR and DLS measurements. Phototriggered unfolding of bacteriorhodopsin, occurring through alpha(II) --> alpha(I) and reverse beta-turn --> extended beta-strand transitions, requires approximately 20 s for completion, while light-induced refolding requires a somewhat longer 80 s as the membrane protein repartitions into the reformed bilayer membrane. Each of these conformational changes can be precisely and reversibly controlled with simple light illumination, providing a novel technique to probe membrane protein folding.
通过紫外可见光谱、傅里叶变换红外光谱、³¹P核磁共振光谱以及动态光散射（DLS）测量，证明了在存在光响应表面活性剂的情况下细菌视紫红质构象的光可逆控制。基于偶氮苯的表面活性剂在434 nm可见光（反式，相对疏水）和350 nm紫外光（顺式，相对亲水）照射下发生光异构化，从而使表面活性剂的胶束化得以可逆控制。这导致膜蛋白在可见光下以未折叠状态分配到胶束中，而紫外光则导致蛋白在折叠状态下溶解于紫色膜双层中。通过核磁共振和动态光散射测量研究了紫色膜 - 光响应表面活性剂相互作用的三阶段模型。细菌视紫红质的光触发解折叠通过α(II)→α(I)和反向β-转角→延伸β-链转变发生，完成需要约20秒，而光诱导的重新折叠需要稍长的80秒，因为膜蛋白重新分配到重新形成的双层膜中。这些构象变化中的每一个都可以通过简单的光照精确且可逆地控制，为探测膜蛋白折叠提供了一种新技术。
