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ID: 124582.0, MPI für biophysikalische Chemie / Molekulare Biologie (Dr. Thomas M. Jovin)
Strong bending of purple membranes in the M-state
Authors:Porschke, D.
Date of Publication (YYYY-MM-DD):2003-08-15
Title of Journal:Journal of Molecular Biology
Issue / Number:3
Start Page:667
End Page:679
Review Status:not specified
Audience:Not Specified
Abstract / Description:Structure changes of purple membranes during the photocycle were analysed in solution by measurements of the electric dichroism. The D96Nmutant was used to characterize the M-state at neutral pH. The transition from the resting state to 61% photo-stationary M-state is associated with a strong reduction of the dichroism decay time constant by a factor of ~2. Because the change of the time constant is independent of the bacteriorhodopsin concentration, the effect is not attributed to light-induced dissociation but to light-induced bending of purple membranes. After termination of light-activation the dichroism decay of the resting state is restored with a time constant close to that of the M-state decay, which is more than two orders of magnitude slower than proton transfer to the bulk. Thus, bending is not due to asymmetric protonation but to the structure of the M-state. A very similar reduction of decay time constants at a corresponding degree of light-activation was found for wild-type bacteriorhodopsin at pH-values 7.8–9.3, where the lifetime of the M-state is extended. Light-induced bending is also reflected in changes of the stationary dichroism, whereas the overall permanent dipole moment remains almost constant, suggesting compensation of changes in molecular and global contributions. Bead model simulations indicate that disks of ~1 mm diameter are bent at a degree of photo-activation of 61% to a radius of ~0.25 mm, assuming a cylindrical bending modus. The large light-induced bending effect is consistent with light-induced opening of the protein on the cytoplasmic side of the membrane detected by electron crystallography, which is amplified due to coupling of monomers in the membrane. Bending may function as a mechanical signal.
Free Keywords:electric dichroism; rotational diffusion; bead model simulation;
D96N; dipole moment
Comment of the Author/Creator:Date: 2003, AUG 15
Last Change of the Resource (YYYY-MM-DD):2004-07-28
External Publication Status:published
Document Type:Article
Communicated by:N. N.
Affiliations:MPI für biophysikalische Chemie/AG Dietmar Pörschke
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