Document Detail

Proton translocation by bacteriorhodopsin in the absence of substantial conformational changes.
MedLine Citation:
PMID:  12051928     Owner:  NLM     Status:  MEDLINE    
Unlike wild-type bacteriorhodopsin (BR), the BR triple mutant D96G/F171C/F219L has been shown to undergo only minor structural rearrangements during its photocycle. Nonetheless, the mutant is capable of transporting protons at a rate of 125(+/-40) H+/BR per minute under light-saturating conditions. Light adaptation of the triple mutant's retinal proceeds in a pH-dependent manner up to a maximum of 63% all-trans. These two findings imply that the transport activity of the triple mutant comprises 66% of the wild-type activity. Time-resolved spectroscopy reveals that the identity and sequence of intermediates in the photocycle of the triple mutant in the all-trans configuration correspond to that of wild-type BR. The only differences relate to a slower rise and decay of the M and O intermediates, and a significant spectral contribution from a 13-cis component. No indication for accumulation of the N intermediate is found under a variety of conditions that normally favor the formation of this species in wild-type BR. The Fourier transform infrared (FTIR) spectrum of the M intermediate in the triple mutant resembles that of wild type. Minor changes in the amide I region during the photocycle suggest that only small movements of the protein backbone occur. Electron microscopy reveals large differences in conformation between the unilluminated state of the mutant protein and wild-type but no light-induced changes in time-resolved measurements. Evidently, proton transport by the triple mutant does not require the major conformational rearrangements that occur on the same time-scale with wild-type. Thus, we conclude that large conformational changes observed in the photocycle of the wild-type and many BR mutants are not a prerequisite for the change in accessibility of the Schiff base nitrogen atom that must occur during vectorial catalysis to allow proton transport.
J Tittor; S Paula; S Subramaniam; J Heberle; R Henderson; D Oesterhelt
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  Journal of molecular biology     Volume:  319     ISSN:  0022-2836     ISO Abbreviation:  J. Mol. Biol.     Publication Date:  2002 May 
Date Detail:
Created Date:  2002-06-07     Completed Date:  2002-07-16     Revised Date:  2006-11-15    
Medline Journal Info:
Nlm Unique ID:  2985088R     Medline TA:  J Mol Biol     Country:  England    
Other Details:
Languages:  eng     Pagination:  555-65     Citation Subset:  IM    
Copyright Information:
Copyright 2002 Elsevier Science Ltd.
Max-Planck-Institut für Biochemie, 82152 Martinsried, Germany.
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MeSH Terms
Archaea / chemistry*
Azides / pharmacology
Bacteriorhodopsins / chemistry*,  genetics,  metabolism*,  ultrastructure
Hydrogen-Ion Concentration
Ion Transport / drug effects,  radiation effects
Microscopy, Electron
Mutation / genetics
Photolysis / drug effects
Protein Conformation / drug effects
Retinaldehyde / chemistry,  metabolism
Spectroscopy, Fourier Transform Infrared
Spectrum Analysis
Reg. No./Substance:
0/Azides; 0/Protons; 116-31-4/Retinaldehyde; 53026-44-1/Bacteriorhodopsins

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