Histidine-rich protein, HPN and metallothionein: are they similar?

Abstract

Helicobacter pylori (H. pylori), a Gram-negative, and spiral-shaped bacterium, has been known to be the causative agent of chronic gastritis and peptic ulcers. The organism produces a large amount of a nickel-containing enzyme urease (~ 10%), which is believed to neutralize gastric acid by producing ammonia for the survival of the bacteria.[1,2] A constant supply of nickel is therefore essential for the synthesis and activity of nickel-containing enzymes. Many histidine-rich proteins and motifs have been found in microorganisms.[2] Hpn (28 His residues out of 60 aa) is a small cytoplasmic protein in H. pylori and is present as a multimer with 20-mer being the predominant species in solution and binds to five Ni2+ and four Bi3+ per monomer moderately (Kd of 7.1 and 11.1 μM respectively).[3] Although in vitro, it binds to Cu2+ stronger than Ni2+ and Bi3+, the in vivo protection by the protein is in the order of Ni2+> Bi3+> Cu2+. [4] Hpn may therefore serve to buffer intracellular Ni2+ in much the same way as that the small and cysteine-rich protein, metallothionein interacts with Zn2+/Cu+ . [5,6] This work was supported by RGC of Hong Kong, Area of Excellence of UGC and the University of Hong Kong! REFERENCES 1. Covacci A, Telford JL, Del Giudice G, Parsonnet J, Rappuoli R (1999) Science 284, 1328-1333. 2. Tomb J-F et al (1997) Nature 388, 539-547. 3. Ge R, Watt RM, Sun X, Tanner JA, He QY, Huang JD, Sun H (2006) Biochem. J. 393, 285-293. 4. Ge R, Zhang Y, Sun X, Watt RM, He QY, Huang JD, Wilcox DE, Sun H (2006) J. Am. Chem. Soc. 128, 11330-11331. 5. Vašák MJ, Hasler DW (2000) Curr. Opin Chem Biol 4, 177-183 6. Wang H, Zheng Q, Cai B, Li H, Sze KH, Huang ZX, Wu HM, Sun H (2006) FEBS Lett. 580, 795-800.