Long-Time Scale Simulations Reveal Key Dynamics That Drive the Onset of the N State in the Proteorhodopsin Photocycle.

Proteorhodopsin (PR) is a microbial proton pump that plays a significant role in phototrophy of bacteria in marine environments. Fundamental understanding of the structure-function relationship that drives proton pumping in PR has largely been elusive due to a lack of high-resolution structures of the photointermediates in the PR photocycle. Extending upon previous work, we used long-time scale molecular dynamics (MD) simulations to characterize the M state of the blue variant of PR, which represents the first proton transfer that takes place in the photocycle.