A His-Asp repeat peptide sequence was identified in a His-rich metal binding protein （HP） produced by a halophilic marine bacterium, Chromohalobacter salexigens DSM 3043^T. A synthetic peptide, PepB20, containing 8 His-Asp repeats showed binding to an Ni-loaded metal-chelating column and elution around 150-200 mM imidazole in the presence of both low （0.15 M） and high （1.5 M） concentrations of NaCl. Addition of Ni or Zn ions at 0.1 to 1 mM resulted in changes in secondary structure of PepB20, leading to metal-induced insoluble aggregation at 1 mM. PepB20 showed different circular dichroism （CD） profiles induced by the binding of Ni or Zn ions, suggesting a formation of different secondary structures by these metal ions. We described metal binding properties and consequent structure changes of PepB20 examined by CD measurements and discuss the possible physiological importance of the His-rich metal binding insertion sequence found in HP.

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