EVIDENCE OF ALPHA-HELIX SLIDINGS DURING BACTERIORHODOPSIN PHOTOCYCLE-ENERGETICS COUPLING

The three-dimensional structure of bacteriorhodopsin indicates that th e all-trans-cis retinal bending causes alpha-helix slidings during the bacteriorhodopsin photocycle. For the elucidation of alpha-helix slid ings taking place during the bacteriorhodopsin photocycle, we calculat ed ASAs of hydrophobic and hydrophilic atoms translocated by alpha-hel ix slidings with thermodynamic criteria found previously. Thermodynami c parameters calculated from ASAs (calculated (Delta)G(transfer) and T DeltaS) mere consistent with those (observed (Delta)G(transfer) and TD eltaS) obtained empirically. These findings indicate that alpha-helix slidings take place during bacteriorhodopsin photocycle-energetics cou pling. These mechanisms not only explain various phenomena, including some mutants forming a long-lived intermediate, but also predict Vario us yet-unobserved phenomena, including the generation of heat in early photocycle intermediates. Copyright (C) 1997 by the Tohoku University Medical Press.