In photosynthetic complexes, tuning of chlorophyll light-absorption spectra by the protein environment is crucial to their efficiency and robustness. Water Soluble Chlorophyll-binding Proteins from Brassicaceae (WSCPs) are useful for studying spectral tuning mechanisms due to their symmetric homotetramer structure, the ability to rigorously modify the chlorophyll’s protein surroundings, and the availability of crystal structures. Here, we present a rigorous analysis based on hybrid Quantum Mechanics and Molecular Mechanics simulations with conformational sampling to quantify the relative contributions of steric and electrostatic factors to the absorption spectra of WSCP-chlorophyll complexes. We show that when considering conformational dynamics, chlorophyll ring deformation accounts for about one-third of the spectral shift, whereas protein electrostatics 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 with desired spectral shift.

中文翻译：

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蛋白质中叶绿素的光谱调谐–静电与环变形

在光合复合物中，通过蛋白质环境调节叶绿素的光吸收光谱对其效率和耐用性至关重要。十字花科的水溶性叶绿素结合蛋白 （WSCP）由于其对称的均四聚体结构，严格修饰叶绿素蛋白质周围环境的能力以及晶体结构的可用性而对于研究光谱调谐机制很有用。在这里，我们提出了基于混合量子力学和分子力学模拟以及构象采样的严格分析，以量化空间和静电因子对WSCP-叶绿素络合物吸收光谱的相对贡献。我们表明，当考虑构象动力学时，叶绿素环变形约占光谱位移的三分之一，而蛋白质静电占其余的三分之二。从实际的角度来看，蛋白质静电比叶绿素构象更易于操纵，因此，