The siderophore-interacting protein YqjH acts as a ferric reductase in different iron assimilation pathways of Escherichia coli

Biochemistry. 2011 Dec 20;50(50):10951-64. doi: 10.1021/bi201517h. Epub 2011 Nov 18.


Siderophore-interacting proteins (SIPs), such as YqjH from Escherichia coli, are widespread among bacteria and commonly associated with iron-dependent induction and siderophore utilization. In this study, we show by detailed biochemical and genetic analyses the reaction mechanism by which the YqjH protein is able to catalyze the release of iron from a variety of iron chelators, including ferric triscatecholates and ferric dicitrate, displaying the highest efficiency for the hydrolyzed ferric enterobactin complex ferric (2,3-dihydroxybenzoylserine)(3). Site-directed mutagenesis revealed that residues K55 and R130 of YqjH are crucial for both substrate binding and reductase activity. The NADPH-dependent iron reduction was found to proceed via single-electron transfer in a double-displacement-type reaction through formation of a transient flavosemiquinone. The capacity to reduce substrates with extremely negative redox potentials, though at low catalytic rates, was studied by displacing the native FAD cofactor with 5-deaza-5-carba-FAD, which is restricted to a two-electron transfer. In the presence of the reconstituted noncatalytic protein, the ferric enterobactin midpoint potential increased remarkably and partially overlapped with the effective E(1) redox range. Concurrently, the observed molar ratios of generated Fe(II) versus NADPH were found to be ~1.5-fold higher for hydrolyzed ferric triscatecholates and ferric dicitrate than for ferric enterobactin. Further, combination of a chromosomal yqjH deletion with entC single- and entC fes double-deletion backgrounds showed the impact of yqjH on growth during supplementation with ferric siderophore substrates. Thus, YqjH enhances siderophore utilization in different iron acquisition pathways, including assimilation of low-potential ferric substrates that are not reduced by common cellular cofactors.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Biocatalysis
  • Circular Dichroism
  • Enterobactin / metabolism
  • Escherichia coli K12 / enzymology*
  • Escherichia coli K12 / growth & development
  • Escherichia coli K12 / metabolism*
  • Escherichia coli Proteins / chemistry
  • Escherichia coli Proteins / genetics
  • Escherichia coli Proteins / metabolism*
  • FMN Reductase / chemistry
  • FMN Reductase / genetics
  • FMN Reductase / metabolism*
  • Ferric Compounds / metabolism*
  • Iron / metabolism*
  • Iron Chelating Agents / metabolism
  • Kinetics
  • Molecular Sequence Data
  • Mutagenesis, Site-Directed
  • Mutant Proteins / chemistry
  • Mutant Proteins / metabolism
  • NADH, NADPH Oxidoreductases / chemistry
  • NADH, NADPH Oxidoreductases / genetics
  • NADH, NADPH Oxidoreductases / metabolism*
  • Oxidation-Reduction
  • Protein Conformation
  • Recombinant Proteins / chemistry
  • Recombinant Proteins / metabolism
  • Sequence Alignment
  • Siderophores / metabolism*
  • Substrate Specificity


  • Escherichia coli Proteins
  • Ferric Compounds
  • Iron Chelating Agents
  • Mutant Proteins
  • Recombinant Proteins
  • Siderophores
  • Enterobactin
  • Iron
  • FMN Reductase
  • NADH, NADPH Oxidoreductases
  • YqjH protein, E coli
  • ferric citrate iron reductase