Adsorption of cadmium ion and gallium ion to immobilized metallothionein fusion protein.
A fusion protein made from maltose binding protein (pmal) and human metallothionein (MT) was expressed using E. coli. The purified recombinant protein (pmal-MT) was immobilized on Chitopearl resin, and characteristics of pmal-MT for metal binding were evaluated. As expected from the tertiary structure of metallothionein, the pmal-MT ligand adsorbed 12.1 cadmium molecules per one molecule of the ligand at pH 5.2. The pmal-MT ligand also bound 26.6 gallium molecules per one molecule of the ligand at pH 6.5. Neither cadmium ion nor gallium ion bound to a control protein bovine serum albumin (BSA). Adsorption isotherms for both ions were correlated by Langmuir-type equations. Two types of binding sites have been elucidated on the basis of HSAB (hard and soft acid and base) theory. It was suggested that gallium ion specifically binds to amino acid residues containing oxygen and nitrogen atoms, while cadmium ion binds to specific binding sites formed by multiple cysteine residues. The pmal-MT ligand bound these metals in the concentration range of 0.2-1.0 mM, and the bound metal ions could be eluted under relatively mild conditions (pH 2.0). The pmal-MT Chitopearl resin was stable and could be used repeatedly without loss of binding activity. Thus, this new ligand would be useful for recovery of toxic heavy metals and/or valuable metal ions from various aqueous solutions.
Terashima
Masaaki
M
Department of Chemical Engineering, Graduate School of Engineering, Osaka Prefecture University, 1-1, Gakuen-cho, Sakai, Osaka 599-8531, Japan. terasima@chemeng.osakafu-u.ac.jp
Oka
Noriyuki
N
Sei
Takamasa
T
Yoshida
Hiroyuki
H
D000327:Adsorption; D001665:Binding Sites; D002104:Cadmium / Q000737:chemistry / Q000302:isolation & purification*; D002352:Carrier Proteins / Q000737:chemistry; D002614:Chelating Agents / Q000737:chemistry; D005708:Gallium / Q000737:chemistry / Q000302:isolation & purification*; D006863:Hydrogen-Ion Concentration; D058619:Maltose-Binding Proteins; D008668:Metallothionein / Q000737:chemistry*; D011993:Recombinant Fusion Proteins / Q000737:chemistry*
D002352:Carrier Proteins; D002614:Chelating Agents; D058619:Maltose-Binding Proteins; D011993:Recombinant Fusion Proteins; D002104:Cadmium; D008668:Metallothionein; D005708:Gallium