Evidence of α-Helix Slidings during Bacteriorhodopsin Photocycle-Energetics Coupling

Abstract

The three-dimensional structure of bacteriorhodopsin indicates that the all-trans-cis retinal bending causes α-helix slidings during the bacteriorhodopsin photocycle. For the elucidation of α-helix slidings taking place during the bacteriorhodopsin photocycle, we calculated ASAs of hydrophobic and hydrophilic atoms translocated by α-helix slidings with thermodynamic criteria found previously. Thermodynamic parameters calculated from ASAs (calculated ΔGtransfer and TΔS) were consistent with those (observed ΔGtransfer and TΔS) obtained empirically. These findings indicate that α-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 © 1997 by the Tohoku University Medical Press.