4.6 Article

Biochemical Similarities and Differences between the Catalytic [4Fe-4S] Cluster Containing Fumarases FumA and FumB from Escherichia coli

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PLOS ONE
卷 8, 期 2, 页码 -

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PUBLIC LIBRARY SCIENCE
DOI: 10.1371/journal.pone.0055549

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  1. Netherlands Ministry of Economic Affairs
  2. B-Basic partner organizations through B-Basic, a public-private NWO-ACTS programme (ACTS = Advanced Chemical Technologies for Sustainability)

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Background: The highly homologous [4Fe-4S] containing fumarases FumA and FumB, sharing 90% amino acid sequence identity, from Escherichia coli are differentially regulated, which suggests a difference in their physiological function. The ratio of FumB over FumA expression levels increases by one to two orders of magnitude upon change from aerobic to anaerobic growth conditions. Methodology/Principal Findings: To understand this difference in terms of structure-function relations, catalytic and thermodynamic properties were determined for the two enzymes obtained from homologous overexpression systems. FumA and FumB are essentially identical in their Michaelis-Menten kinetics of the reversible fumarate to L-malate conversion; however, FumB has a significantly greater catalytic efficiency for the conversion of D-tartrate to oxaloacetate consistent with the requirement of the fumB gene for growth on D-tartrate. Reduction potentials of the [4Fe-4S](2+) Lewis acid active centre were determined in mediated bulk titrations in the presence of added substrate and were found to be approximately 2290 mV for both FumA and FumB. Conclusions/Significance: This study contradicts previously published claims that FumA and FumB exhibit different catalytic preferences for the natural substrates L-malate and fumarate. FumA and FumB differ significantly only in the catalytic efficiency for the conversion of D-tartrate, a supposedly non-natural substrate. The reduction potential of the substrate-bound [4Fe-4S] active centre is, contrary to previously reported values, close to the cellular redox potential.

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