Mechanisms of the Opsin Shift

质子化的视网膜希夫碱在溶液中与载脂蛋白结合时吸收最大值的移动，即所谓的视蛋白移动，是蛋白质结合口袋中发色团与其环境之间特殊相互作用的最明显证据。过去提出的解释视蛋白位移起源的机制无法得到适当的检验，因为这些结构在很大程度上是假设的，而且没有用于光谱定量计算的计算工具。随着视网膜结合蛋白x射线结构的可用性和可靠的量子力学方法的发展，计算包括部分蛋白质结合袋的视网膜发色团的激发态已经成为可能。该提议的目的是在不同蛋白质环境下视网膜发色团激发态的非经验计算和CASPT2校正多构型SCF波函数的基础上。在已知x射线数据的约束下，将优化发色团的几何形状。根据计算资源的不同，环境将包含在计算中。在这些计算的基础上，将研究视蛋白转移的不同机制，并评估它们的相对贡献。计算结果将用于验证，通过紫外/可见和CD光谱，为紫红质和bR光循环的中间体提出的结构。

The shift of the absorption maximum of a protonated retinal Schiff base in solution upon binding to the apoprotein, the so-called opsin shift, is the most conspicuous evidence of the special interaction between the chromophore and its environment in the protein binding pocket. Mechanisms which have been proposed in the past to expiain the origin of the opsin shift could not be tested properly, since the structures were largely hypothetical and computational tools for quantitative calculation of the spectra were not available. With the availability of X-ray structures of retinal binding proteins and the development of reliable quantum-mechanical methods the calculation of excited states of the retinal chromophore including parts of the protein binding pocket has become feasible.The objective of the proposal is the non-empirical calculation of the excited states of the retinal chromophore in different protein environments an the basis of CASPT2 corrected muiticonfigurational SCF wavefunctions. Chromophore geometries will be optimized subject to the constraints of the known X-ray data. The environment will be included in the calculations depending an the computational resources. On the basis of these calculations the different mechanisms of the opsin shift will be studied and their relative contributions evaluated. The calculations will be used to validate, via the UV/Vis and CD spectra, the structures propesed for the intermediates of the rhodopsin and the bR photocycles.