Fritz Haber Center for Molecular Dynamics Research, Institute of Chemistry, The Hebrew University of Jerusalem, Jerusalem, 9190401, Israel.
DTU Chemistry, Technical University of Denmark, DK-2800, Kongens Lyngby, Denmark.
Chemistry. 2022 May 16;28(28):e202200139. doi: 10.1002/chem.202200139. Epub 2022 Apr 5.
Proteorhodopsin (PR) is a photoactive proton pump found in marine bacteria. There are two phenotypes of PR exhibiting an environmental adaptation to the ocean's depth which tunes their maximum absorption: blue-absorbing proteorhodopsin (BPR) and green-absorbing proteorhodopsin (GPR). This blue/green color-shift is controlled by a glutamine to leucine substitution at position 105 which accounts for a 20 nm shift. Typically, spectral tuning in rhodopsins is rationalized by the external point charge model but the Q105L mutation is charge neutral. To study this tuning mechanism, we employed the hybrid QM/MM method with sampling from molecular dynamics. Our results reveal that the positive partial charge of glutamine near the C -C bond of retinal shortens the effective conjugation length of the chromophore compared to the leucine residue. The derived mechanism can be applied to explain the color regulation in other retinal proteins and can serve as a guideline for rational design of spectral shifts.
紫膜质体（PR）是一种在海洋细菌中发现的光活性质子泵。有两种表型的 PR 对海洋深度的环境适应进行了调整，从而调整了它们的最大吸收：蓝光吸收紫膜质体（BPR）和绿光吸收紫膜质体（GPR）。这种蓝/绿颜色的移动是由 105 位的谷氨酰胺到亮氨酸取代控制的，这导致了 20nm 的移动。通常，视紫红质的光谱调谐可以通过外部点电荷模型来解释，但 Q105L 突变是电荷中性的。为了研究这种调谐机制，我们采用了混合量子力学/分子力学方法，并从分子动力学中进行了采样。我们的结果表明，视黄醛 C-C 键附近谷氨酰胺的正部分电荷与亮氨酸残基相比，缩短了发色团的有效共轭长度。这种衍生的机制可以应用于解释其他视蛋白中的颜色调节，并可以作为光谱位移的合理设计的指导方针。
