Photodynamics of Microbial Rhodopsin Mimic M1-L121E: Insights from Computational Modeling

Understanding the photodynamics of rhodopsin is crucial for elucidating light-induced biological processes. This study investigates the excited-state properties and isomerization dynamics of the microbial rhodopsin mimic protein, focusing on its all-trans (AT) and 13-cis (13C) conformations. By scanning the C13═C14 dihedral angle, we revealed distinct isomerization pathways for the two conformations. In the all-trans conformation, the crossing of S1 and S2 energy levels results in significant electronic state mixing, slowing the isomerization rate and extending the excited-state lifetime. Furthermore, the interaction between the chromophore and the protein varies markedly between the conformations, it is attractive in the 13-cis conformations, but repulsive near the mutation site in the all-trans conformations. These findings suggest that the repulsive force in the all-trans conformations may influence ground-state stability, indirectly affecting the excited-state isomerization process.