Evidence of alpha-helix slidings during bacteriorhodopsin photocycle-energetics coupling

The three-dimensional structure of bacteriorhodopsin indicates that the all-trans-cis retinal bending causes alpha-helix slidings during the bacteriorhodopsin photocycle. For the elucidation of alpha-helix slidings taking place during the bacteriorhodopsin photocycle, we calculated ASAs of hydrophobic and hydrophilic atoms translocated by alpha-helix slidings with thermodynamic criteria found previously. Thermodynamic parameters calculated from ASAs (calculated delta Gtransfer and T delta S) were consistent with those (observed delta Gtransfer and T delta S) obtained empirically. These findings indicate that alpha-helix slidings take place during bacteriorhodopsin photocycle-energetics coupling. These mechanisms not only explain various phenomena, including some mutants forming a long-lived intermediate, but also predict various yet-unobserved phenomena, including the generation of heat in early photocycle intermediates.