Thermodynamic and Kinetic Aspects of Metal Binding to the Histidine-rich Protein, Hpn

Abstract

The histidine-rich protein, Hpn, binds to essential metals Ni2+, Cu2+, Zn2+ and a therapeutic metal Bi3+ with the in vitro affinities in the order of Cu2+ > Ni2+ > Bi3+ > Zn2+. In contrast, the in vivo (in E. coli) protection by the protein is in the order of Ni2+ > Bi3+ > Cu2+ approximately Zn2+. The release of Ni2+ from the protein follows a two-step process consisting of a rapidly established equilibrium and subsequently a rate-determining step (dissociation of Hpn-Ni...EDTA to Ni-EDTA). Our work suggests the nickel storage and homeostasis in H. pylori as the primary role of Hpn.

Metal‐Binding Properties of an Hpn‐Like Histidine‐Rich Protein

“…It shows that the peptide also migrated much more slowly than expected, that is, the peptide migrated to a position that corresponded to the molecular mass of 32 kDa, which is around 10 times larger than its theoretical mass of 2.9 kDa. Since the peptide is only histidine-rich and this migration feature is often noted in His-rich proteins (see Table S2 in the Supporting Information), [11,12,[26][27][28][29][30][31] we propose that the propensity to form a high-order multimer of Hpnl is caused by its high percentage of histidines rather than glutamine residues in the protein sequence. Moreover, since His-rich domains in protein can also interact with other ligands such as haem, heparin, plasmin, and IgG to regulate critical biological processes, [32,33] the histidines in Hpnl may facilitate the formation of oligomers by either aligning or stacking on the top of each other.…”

“…[4] Therefore, H. pylori has developed a series of sophisticated processes to sense cellular nickel ions and take up these nutrients by means of a nickel-specific permease NixA [5] and an ATPbinding cassette-type transporter AbcABCD, [6] a nickel-dependent regulator NikR, [7] accessory proteins UreIEFGH [8,9] and HypA C H T U N G T R E N N U N G ABCDEF [9,10] for activation of urease and hydrogenase, storage proteins Hpn [11] and Hpn-like (Hpnl), [12] and the efflux system CznABC. [13] Recent transcriptome analysis showed that the hpnl gene in H. pylori is up-regulated by NikR and ArsRS at transcriptional levels in the presence of appropriate amounts of nickel ions.…”

Metallomics: An integrated biometal science

“…The protein plays an important role in the metabolism, homeostatic control, and detoxification of a number of essential (Zn(Ⅱ), Cu(Ⅰ)) or toxic (Cd(Ⅱ), Hg(Ⅱ), As(Ⅲ/Ⅴ)) trace elements. Similarly, a group of histidine-rich proteins from Helicobacter pylori have been studied in our group [48][49][50][51] . For H. pylori, the nickel-containing enzymes urease and hydrogenase are essential for its colonization in the acidic environment in the stomach, and thus a constant supply of nickel ions is required for the synthesis and activity of these enzymes [9] .…”

UreE-UreG Complex Facilitates Nickel Transfer and Preactivates GTPase of UreG in Helicobacter pylori

“…The utilization of nickel must be tightly controlled in H. pylori as a plethora of nickel causes serious cell damage to H. pylori (9). Therefore, H. pylori has developed an elaborate system to tightly regulate the cellular nickel homeostasis from uptake, storage, and delivery to efflux through biosynthesis of a series of metalloproteins and chaperones (10), such as nickel storage protein Hpn and Hpnl (11)(12)(13)(14), which are only produced by this pathogen, and HspA (15,16), which has a distinct His-Cys-rich C terminus with nickel binding ability.…”