Document Detail

Molecular basis for enzymatic sulfite oxidation: how three conserved active site residues shape enzyme activity.
MedLine Citation:
PMID:  19004819     Owner:  NLM     Status:  MEDLINE    
Sulfite dehydrogenases (SDHs) catalyze the oxidation and detoxification of sulfite to sulfate, a reaction critical to all forms of life. Sulfite-oxidizing enzymes contain three conserved active site amino acids (Arg-55, His-57, and Tyr-236) that are crucial for catalytic competency. Here we have studied the kinetic and structural effects of two novel and one previously reported substitution (R55M, H57A, Y236F) in these residues on SDH catalysis. Both Arg-55 and His-57 were found to have key roles in substrate binding. An R55M substitution increased Km(sulfite)(app) by 2-3 orders of magnitude, whereas His-57 was required for maintaining a high substrate affinity at low pH when the imidazole ring is fully protonated. This effect may be mediated by interactions of His-57 with Arg-55 that stabilize the position of the Arg-55 side chain or, alternatively, may reflect changes in the protonation state of sulfite. Unlike what is seen for SDHWT and SDHY236F, the catalytic turnover rates of SDH R55M and SDHH57A are relatively insensitive to pH (approximately 60 and 200 s(-1), respectively). On the structural level, striking kinetic effects appeared to correlate with disorder (in SDHH57A and SDHY236F) or absence of Arg-55 (SDHR55M), suggesting that Arg-55 and the hydrogen bonding interactions it engages in are crucial for substrate binding and catalysis. The structure of SDHR55M has sulfate bound at the active site, a fact that coincides with a significant increase in the inhibitory effect of sulfate in SDHR55M. Thus, Arg-55 also appears to be involved in enabling discrimination between the substrate and product in SDH.
Susan Bailey; Trevor Rapson; Kayunta Johnson-Winters; Andrei V Astashkin; John H Enemark; Ulrike Kappler
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Publication Detail:
Type:  Journal Article; Research Support, N.I.H., Extramural; Research Support, Non-U.S. Gov't; Research Support, U.S. Gov't, Non-P.H.S.     Date:  2008-11-12
Journal Detail:
Title:  The Journal of biological chemistry     Volume:  284     ISSN:  0021-9258     ISO Abbreviation:  J. Biol. Chem.     Publication Date:  2009 Jan 
Date Detail:
Created Date:  2009-01-19     Completed Date:  2009-03-23     Revised Date:  2013-06-04    
Medline Journal Info:
Nlm Unique ID:  2985121R     Medline TA:  J Biol Chem     Country:  United States    
Other Details:
Languages:  eng     Pagination:  2053-63     Citation Subset:  IM    
Molecular Biophysics Group, Science and Technology Facilities Council Daresbury Laboratory, Warrington WA4 4AD, United Kingdom.
Data Bank Information
Bank Name/Acc. No.:
PDB/2CA3;  2CA4
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MeSH Terms
Alphaproteobacteria / enzymology,  genetics
Catalytic Domain*
Crystallography, X-Ray
Electron Spin Resonance Spectroscopy
Hydrogen-Ion Concentration
Models, Molecular
Mutation / genetics
Protein Structure, Quaternary
Protein Structure, Tertiary
Sulfite Dehydrogenase / chemistry*,  genetics,  metabolism*
Sulfites / chemistry*,  metabolism*
Grant Support
Reg. No./Substance:
0/Sulfites; EC Dehydrogenase

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine

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