engleski

Exploring the copper affinity toward the CrdA protein from Helicobacter pylori

Adaptation of Helicobacter pylori to the conditions in the gastric mucosa involves acquisition mechanisms that can overcome a temporary lack of essential metal ions. Several proteins are involved in the transport of copper ions and in control of the concentration of free copper ions in the cytoplasm below toxic values. Among them are P-type ATPase CopA [1], HP1326 (CrdA), HP1327 (CrdB), HP1328, and HP1329 [2]. In this research we structurally characterized the CrdA protein from Helicobacter pylori (HpCrdA) and we explored its binding affinity toward copper ions. CD measurements confirmed the major contribution of -sheets in the HpCrdA structure. The modeled HpCrdA structure showed a conserved methionine-rich region, a potential binding site for Cu(I) (Fig. 1), as in the structures of similar copper-binding proteins, CopC and PcoC, from Pseudomonas syringae and from Escherichia coli, respectively. In contrast to CopC and PcoC, HpCrdA contains two additional methionines and two glutamic acid residues (MMXEMPGMXXMXEM) in the conserved amino acid motif but lacks the canonical Cu(II) binding site (two histidine residues). Since the position of the methionine-rich site is in a flexible loop it can adopt different geometries for the two copper oxidation states. Based on the copper affinity studies we concluded that HpCrdA binds copper in both oxidation states (I and II), but with different binding affinities, micromolar was found for Cu(II), and less than nanomolar was proposed for Cu(I).

protein, CrdA, interaction, copper ions

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