The role of HBP23 to chronic myelogenous keukemia

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HBP23, heme-binding protein 23, is a member of 2-Cys peroxiredoxin family, and exhibits a peroxidase activity. The crystal Structure shows that Cys52 forms the intermolecular disulfide with Cys173 from another subunit by C-terminal tail swapping in the oxidized form, being surrounded by several hydrophobic residues and the conserved Arg128 and Arg151 in the active site pocket {S.Hirotsu et al.(1999) Proc.Natl.Acad.Sd.U.S.A. 96, 12333-12338}. In this work, we studied the relationships between HBP23 and peroxidase activity, and non-receptor tyrosine kinase c-Abl. HBP23 and the variants prepared by using site-directed mutagenesis. All proteins were overexpressed in E.coli. Non-receptor tyrosine kinase c-Abl was overexpressed in baculovirus-insect cell system. Size-exclusion chromatographic analysis showed that the quaternary structure of HBP23 exchanged ranging from the decamer to the dimer, depending on redox and protein concentration/ionic strength. Peroxidase activity was measured by two systems, thioredoxin system and DTT system. Cys52 was the site for oxidation by peroxides. For the complex formation, thioredoxin required Cys173 of HBP23. Arg128 and Arg151 were required for the reactivity of Cys52. HBP23 formed non-receptor tyrosin kinase, like the human homologue.