Format

Send to

Choose Destination
Biophys J. 2001 Jun;80(6):2856-66.

Time-resolved detection of transient movement of helices F and G in doubly spin-labeled bacteriorhodopsin.

Author information

1
Lehrstuhl für Biophysik, Ruhr-Universität Bochum, D-44780 Bochum, Germany.

Abstract

Photo-excited structural changes of the light-driven proton pump bacteriorhodopsin were monitored using double-site-directed spin labeling combined with electron paramagnetic resonance (EPR) spectroscopy. The inter-spin distances between nitroxides attached at residue positions 100 and 226, 101 and 160, and 101 and 168 were determined for the BR initial state and the trapped M photo-intermediate. Distance changes that occur during the photocycle were followed with millisecond time resolution under physiological conditions at 293 K. The kinetic analysis of the EPR data and comparison with the absorbance changes in the visible spectrum reveal an outward movement of helix F during the late M intermediate and a subsequent approach of helix G toward the proton channel. The displacements of the cytoplasmic moieties of these helices amount to 0.1-0.2 nm. We propose that the resulting opening of the proton channel decreases the pK of the proton donor D96 and facilitates proton transfer to the Schiff base during the M-to-N transition.

PMID:
11371459
PMCID:
PMC1301470
DOI:
10.1016/S0006-3495(01)76252-2
[Indexed for MEDLINE]
Free PMC Article

Supplemental Content

Full text links

Icon for Elsevier Science Icon for PubMed Central
Loading ...
Support Center