Binding Capacity of Halophilic Histidine-rich Metal-binding Protein and Potential Application for Bio-sorption of Heavy-metals from Saline Environments

摘要

His-rich metal binding protein (HP) from halophilic marine bacterium Chromohalobacter salexigens has been characterized by its unique insertion sequence consisting of 46 amino acid residues, IS46 with abundant His residues, identified from the sequence comparison with well-studied other metal binding proteins such as TroA from Treponema pallidum. Here, we carried out equilibrium dialysis of HP against buffer solutions containing Zn, Cu, Ni or Mn ions for quantitative determination of the metal-binding capacity of HP. It was found that a maximum 10 molecules of Zn, Cu or Ni ions was bound to one molecule of HP under the saturated conditions. The affinity of metal ions to HP was Zn > Cu > Ni > Mn. We further examined the potential use of HP for bio-sorption of metal ions in saline environments. His-tagged HP-immobilized Sepharose column bound 9.5 Ni ions per one molecule of the immobilized protein, suggesting possible applications of HP for bio-sorption and recovery of heavy metal ions under saline conditions.