Relationship between Ni(II) and Zn(II) coordination and nucleotide binding by the Helicobacter pylori [NiFe]-hydrogenase and urease maturation factor HypB [Protein Structure and Folding]

December 12th, 2013 by Sydor, A. M., Lebrette, H., Ariyakumaran, R., Cavazza, C., Zamble, D. B.

The pathogen Helicobacter pylori requires two nickel-containing enzymes, urease and [NiFe]-hydrogenase, for efficient colonization of the human gastric mucosa. These enzymes possess complex metallocenters that are assembled by teams of proteins in multi-step pathways. One essential accessory protein is the GTPase HypB, which is required for Ni(II) delivery to [NiFe]-hydrogenase and also participates in urease maturation. Ni(II) or Zn(II) binding to a site embedded in the GTPase domain of HypB modulates the enzymatic activity, suggesting a mechanism of regulation. In this study, biochemical and structural analysis of H. pylori HypB (HpHypB) reveal an intricate link between nucleotide and metal binding. HpHypB nickel coordination, stoichiometry, and affinity are modulated by GTP and GDP, an effect not observed for zinc, and biochemical evidence suggests that His107 coordination to nickel toggles on and off in a nucleotide-dependent manner. These results are consistent with the crystal structure of HpHypB loaded with Ni(II), GDP, and Pi, which reveals a nickel site distinct from that of zinc-loaded Methanocaldococcus jannaschii HypB as well as subtle changes to the protein structure. Furthermore, Cys142, a metal ligand from the Switch II GTPase motif, is identified as a key component of the signal transduction between metal binding and the enzymatic activity. Finally, potassium accelerates the enzymatic activity of HpHypB, but has no effect on the other biochemical properties of the protein. Altogether, this molecular-level information about HpHypB provides insight into its cellular function and illuminates a possible mechanism of metal ion discrimination.
  • Posted in Journal of Biological Chemistry, Publications
  • Comments Off on Relationship between Ni(II) and Zn(II) coordination and nucleotide binding by the Helicobacter pylori [NiFe]-hydrogenase and urease maturation factor HypB [Protein Structure and Folding]