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Changes in hydrogen-bond strengths explain reduction potentials in 10 rubredoxin variants.

Authors
  • Lin, I-Jin
  • Gebel, Erika B
  • Machonkin, Timothy E
  • Westler, William M
  • Markley, John L
Type
Published Article
Journal
Proceedings of the National Academy of Sciences
Publisher
Proceedings of the National Academy of Sciences
Publication Date
Oct 11, 2005
Volume
102
Issue
41
Pages
14581–14586
Identifiers
PMID: 16199518
Source
Medline
License
Unknown

Abstract

The rubredoxin from Clostridium pasteurianum (CpRd) provides an excellent system for investigating how the protein sequence modulates the reduction potential of the active site in an iron-sulfur protein. (15)N NMR spectroscopy has allowed us to determine with unprecedented accuracy the strengths of all six key hydrogen bonds between protein backbone amides and the sulfur atoms of the four cysteine residues that ligate the iron in the oxidized (Fe(III)) and reduced (Fe(II)) forms of wild-type CpRd and nine mutants (V44G, V44A, V44I, V44L, V8G, V8A, V8I, V8L, and V8G/V44G). The length (or strength) of each hydrogen bond was inferred from the magnitude of electron spin delocalized across the hydrogen bond from the iron atom onto the nitrogen. The aggregate lengths of these six hydrogen bonds are shorter in both oxidation states in variants with higher reduction potential than in those with lower reduction potential. Differences in aggregate hydrogen bonding upon reduction correlate linearly with the published reduction potentials for the 10 CpRd variants, which span 126 mV. Sequence effects on the reduction potential can be explained fully by their influence on hydrogen-bond strengths.

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