Purification and characterization of metallothionein protein in marine catfish, Arius arius , on exposure to cadmium

Fishes are bio-concentrators for heavy metals, but cannot thrive in excessively polluted water. Heavy metals can accumulate in Arius arius , and cadmium (Cd) activates its metal-binding protein. Presently, Cd-binding metallothionein (MT) in A. arius is subjected to sub-lethal cadmium chloride (CdCl 2 at 20 mg/L for 72 h). Separation of MT was achieved from liver homogenate supernatants via affinity chromatography and Sephadex G-25, assessed by 15% SDS-PAGE, verified by Western blotting, and quantified by MALDI-TOF. Using mass fingerprinting, peptide masses were searched in Swiss-Prot. A. arius bounded MT amino acid sequences matched Oreochromis mossambicus with 100%. The 60 amino acids of MT and cysteine content were identified (20 residues). MT contains 6021 daltons based on the MALDI-TOF–MS. The MT protein was modeled using modular9v8 software, confirmed using Ramachandran plot, and utilized as a biomarker for Cd toxicity in fish. The 3D structures might help to identify the binding sites and may lead to innovative treatments for stress and cadmium toxicity.