Fritz Haber Centre for Molecular Dynamics Research, Institute of Chemistry, Hebrew University of Jerusalem, Israel.
Phys Chem Chem Phys. 2021 Mar 21;23(11):6544-6551. doi: 10.1039/d0cp06582j. Epub 2021 Mar 10.
In photosynthetic complexes, tuning of chlorophyll light-absorption spectra by the protein environment is crucial to their efficiency and robustness. Recombinant type II water soluble chlorophyll-binding proteins from Brassicaceae (WSCPs) are useful for studying spectral tuning mechanisms due to their symmetric homotetramer structure, and the ability to rigorously modify the chlorophyll's protein surroundings. Our previous comparison of the crystal structures of two WSCP homologues suggested that protein-induced chlorophyll ring deformation is the predominant spectral tuning mechanism. Here, we implement a more rigorous analysis based on hybrid quantum mechanics and molecular mechanics calculations to quantify the relative contributions of geometrical and electrostatic factors to the absorption spectra of WSCP-chlorophyll complexes. We show that when considering conformational dynamics, geometry distortions such as chlorophyll ring deformation accounts for about one-third of the spectral shift, whereas the direct polarization of the electron density accounts for the remaining two-thirds. From a practical perspective, protein electrostatics is easier to manipulate than chlorophyll conformations, thus, it may be more readily implemented in designing artificial protein-chlorophyll complexes.
在光合作用复合物中，蛋白质环境对叶绿素光吸收光谱的调谐对于其效率和稳健性至关重要。来自十字花科的重组 II 型水溶性叶绿素结合蛋白（WSCP）由于其对称的同四聚体结构以及严格修饰叶绿素蛋白质环境的能力，是研究光谱调谐机制的有用工具。我们之前对两种 WSCP 同源物的晶体结构进行了比较，结果表明，蛋白质诱导的叶绿素环变形是主要的光谱调谐机制。在这里，我们基于混合量子力学和分子力学计算实施了更严格的分析，以量化几何和静电因素对 WSCP-叶绿素复合物吸收光谱的相对贡献。我们表明，当考虑构象动力学时，叶绿素环变形等几何变形约占光谱位移的三分之一，而电子密度的直接极化则占其余三分之二。从实际的角度来看，蛋白质静电比叶绿素构象更容易操纵，因此，在设计人工蛋白-叶绿素复合物时可能更容易实施。
