Nickel Ligation of the N-Terminal Amine of HypA Is Required for Urease Maturation in Helicobacter pylori

Biochemistry. 2017 Feb 28;56(8):1105-1116. doi: 10.1021/acs.biochem.6b00912. Epub 2017 Feb 17.

Abstract

The human pathogen Helicobacter pylori requires nickel for colonization of the acidic environment of the stomach. HypA, a Ni metallochaperone that is typically associated with hydrogenase maturation, is also required for urease maturation and acid survival of H. pylori. There are two proposed Ni site structures for HypA; one is a paramagnetic six-coordinate site characterized by X-ray absorption spectroscopy (XAS) in unmodified HypA, while another is a diamagnetic four-coordinate planar site characterized by solution nuclear magnetic resonance in an N-terminally modified HypA construct. To determine the role of the N-terminal amine in Ni binding of HypA, an N-terminal extension variant, L2*-HypA, in which a leucine residue was inserted into the second position of the amino acid sequence in the proposed Ni-binding motif, was characterized in vitro and in vivo. Structural characterization of the Ni site using XAS showed a coordination change from six-coordinate in wild-type HypA (WT-HypA) to five-coordinate pyramidal in L2*-HypA, which was accompanied by the loss of two N/O donor protein ligands and the addition of an exogenous bromide ligand from the buffer. The magnetic properties of the Ni sites in WT-HypA compared to those of the Ni sites in L2*-HypA confirmed that a spin-state change from high to low spin accompanied this change in structure. The L2*-HypA H. pylori strain was shown to be acid sensitive and deficient in urease activity in vivo. In vitro characterization showed that L2*-HypA did not disrupt the HypA-UreE interaction that is essential for urease maturation but was at least 20-fold weaker in Ni binding than WT-HypA. Characterization of the L2*-HypA variant clearly demonstrates that the N-terminal amine of HypA is involved in proper Ni coordination and is necessary for urease activity and acid survival.

MeSH terms

  • Amines / metabolism*
  • Bacterial Proteins / chemistry*
  • Bacterial Proteins / genetics
  • Bacterial Proteins / metabolism*
  • Carrier Proteins / chemistry*
  • Carrier Proteins / genetics
  • Carrier Proteins / metabolism*
  • Helicobacter pylori / enzymology*
  • Metallochaperones
  • Models, Molecular
  • Mutation
  • Nickel / metabolism*
  • Protein Structure, Quaternary
  • Protein Structure, Secondary
  • Urease / metabolism*

Substances

  • Amines
  • Bacterial Proteins
  • Carrier Proteins
  • HypA protein, Helicobacter pylori
  • Metallochaperones
  • Nickel
  • Urease