Document Detail


Hydrogen bonding between the Q(B) site ubisemiquinone and Ser-L223 in the bacterial reaction center: a combined spectroscopic and computational perspective.
MedLine Citation:
PMID:  23016832     Owner:  NLM     Status:  MEDLINE    
Abstract/OtherAbstract:
In the Q(B) site of the Rhodobacter sphaeroides photosynthetic reaction center, the donation of a hydrogen bond from the hydroxyl group of Ser-L223 to the ubisemiquinone formed after the first flash is debatable. In this study, we use a combination of spectroscopy and quantum mechanics/molecular mechanics (QM/MM) calculations to comprehensively explore this topic. We show that ENDOR, ESEEM, and HYSCORE spectroscopic differences between mutant L223SA and the wild-type sample (WT) are negligible, indicating only minor perturbations in the ubisemiquinone spin density for the mutant sample. Qualitatively, this suggests that a strong hydrogen bond does not exist in the WT between the Ser-L223 hydroxyl group and the semiquinone O(1) atom, as removal of this hydrogen bond in the mutant should cause a significant redistribution of spin density in the semiquinone. We show quantitatively, using QM/MM calculations, that a WT model in which the Ser-L223 hydroxyl group is rotated to prevent hydrogen bond formation with the O(1) atom of the semiquinone predicts negligible change for the L223SA mutant. This, together with the better agreement between key QM/MM calculated and experimental hyperfine couplings for the non-hydrogen-bonded model, leads us to conclude that no strong hydrogen bond is formed between the Ser-L223 hydroxyl group and the semiquinone O(1) atom after the first flash. The implications of this finding for quinone reduction in photosynthetic reaction centers are discussed.
Authors:
Erik Martin; Amgalanbaatar Baldansuren; Tzu-Jen Lin; Rimma I Samoilova; Colin A Wraight; Sergei A Dikanov; Patrick J O'Malley
Publication Detail:
Type:  Journal Article; Research Support, N.I.H., Extramural; Research Support, U.S. Gov't, Non-P.H.S.     Date:  2012-10-30
Journal Detail:
Title:  Biochemistry     Volume:  51     ISSN:  1520-4995     ISO Abbreviation:  Biochemistry     Publication Date:  2012 Nov 
Date Detail:
Created Date:  2013-02-07     Completed Date:  2013-02-21     Revised Date:  2013-12-04    
Medline Journal Info:
Nlm Unique ID:  0370623     Medline TA:  Biochemistry     Country:  United States    
Other Details:
Languages:  eng     Pagination:  9086-93     Citation Subset:  IM    
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MeSH Terms
Descriptor/Qualifier:
Electron Spin Resonance Spectroscopy
Hydrogen Bonding
Photosynthetic Reaction Center Complex Proteins / chemistry,  genetics,  metabolism
Quantum Theory
Rhodobacter sphaeroides / chemistry,  metabolism
Spectrum Analysis
Ubiquinone / analogs & derivatives*,  chemistry,  genetics
Grant Support
ID/Acronym/Agency:
GM062954/GM/NIGMS NIH HHS; R01 GM062954/GM/NIGMS NIH HHS; S10 RR025438/RR/NCRR NIH HHS; S10-RR025438/RR/NCRR NIH HHS; S10-RR15878/RR/NCRR NIH HHS
Chemical
Reg. No./Substance:
0/Photosynthetic Reaction Center Complex Proteins; 1339-63-5/Ubiquinone; 303-98-0/coenzyme Q10
Comments/Corrections

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