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)G(transfer) and TDeltaS) mere consistent with those (observed (Delta)G(transfer) and TDeltaS) 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. Copyright (C) 1997 by the Tohoku University Medical Press.