Abstract
The open reading frame SCO4226 of Streptomyces coelicolor A3(2) encodes an 82-residue hypothetical protein. Biochemical assays revealed that each SCO4226 dimer binds four nickel ions. To decipher the molecular function, we solved the crystal structures of SCO4226 in both apo- and nickel-bound (Ni-SCO4226) forms at 1.30 and 2.04 Å resolution, respectively. Each subunit of SCO4226 dimer adopts a canonical ferredoxin-like fold with five β-strands flanked by two α-helices. In the structure of Ni-SCO4226, four nickel ions are coordinated at the surface of the dimer. Further biochemical assays suggested that the binding of Ni2+ triggers the self-aggregation of SCO4226 in vitro. In addition, RT-qPCR assays demonstrated that the expression of SCO4226 gene in S. coelicolor is specifically up-regulated by the addition of Ni2+, but not other divalent ions such as Cu2+, Mn2+ or Co2+. All these results suggested that SCO4226 acts as a nickel binding protein, probably required for nickel sequestration and/or detoxification.
Highlights
Nickel is first demonstrated as a bacterial growth nutrient for Hydrogenomonas strains [1]
The intracellular accumulation of nickel to millimolar level is toxic to cells, and inhibits the growth of most bacteria [6], which might be due to the induction of reactive oxygen species [7]
Microorganisms evolve a variety of transporters, sensor/regulators and storage proteins to maintain nickel homeostasis [8,9]
Summary
Nickel is first demonstrated as a bacterial growth nutrient for Hydrogenomonas strains [1]. The coordinates and the structure factors of apo- and nickel-SCO4226 are available from the PDB database (accession numbers 4OI3 and 4OI6, respectively). In the structure of Ni-SCO4226, four nickel ions are assigned at the dimer interface, with Ni-1 and Ni-4 on one side, and Ni-2 and Ni-3 on the other (Figure 1B).
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