Aix-Marseille Univ, CNRS, ICR, Marseille, France.
Phys Chem Chem Phys. 2020 Jun 10;22(22):12447-12455. doi: 10.1039/d0cp01714k.
Cryptochromes are a class of flavoproteins proposed as candidates to explain magnetoreception of animals, plants and bacteria. The main hypothesis is that a biradical is formed upon blue-light absorption by flavin adenine dinucleotide (FAD). In a protein milieu, the oxidized form of FAD can be reduced, leading to four redox derivative forms: anionic and neutral semi-reduced radicals, and anionic and neutral fully reduced forms. All these forms have a characteristic electronic absorption spectrum, with a strong vibrational resolution. Here, we carried out a normal mode analysis at the electrostatic embedding QM/MM level of theory to compute the vibrationally resolved absorption spectra of the five redox forms of FAD embedded in a plant cryptochrome. We show that explicitly accounting for vibrational broadening contributions to electronic transitions is essential to reproduce the experimental spectra. In the case of the neutral radical form of FAD, the absorption spectrum is reproduced only if the presence of a tryptophan radical is considered.
隐花色素是一类黄素蛋白，被认为是解释动物、植物和细菌磁受体的候选物质。主要假说是，在吸收蓝光后，黄素腺嘌呤二核苷酸（FAD）形成双自由基。在蛋白质环境中，FAD 的氧化形式可以被还原，导致四种氧化还原衍生物形式：阴离子和中性半还原自由基，以及阴离子和中性完全还原形式。所有这些形式都具有特征性的电子吸收光谱，具有强烈的振动分辨率。在这里，我们在静电嵌入 QM/MM 理论水平上进行了正常模式分析，以计算嵌入在植物隐花色素中的 FAD 的五种氧化还原形式的振动分辨吸收光谱。我们表明，明确考虑振动加宽对电子跃迁的贡献对于重现实验光谱至关重要。在 FAD 的中性自由基形式的情况下，如果考虑色氨酸自由基的存在，则可以重现吸收光谱。
