Cloning, expression and characterization of metallothionein from Antarctic clam Laternula elliptica

Abstract

The genes for two apparent subtypes of metallothioneins (MTs) isoform were isolated from Antarctic clam, Laternula elliptica. Determination of the nucleotide sequence showed that the gene consist of 222 bp that codes a 73-amino acid protein. The comparison between MTs cDNA sequences of L. elliptica and other bivalves shows strong homologies on positions of cysteine residues which are to be important for their metal binding abilities. The gene for the metallothionein was inserted into a pET vector and overexpressed as carboxyl terminal extension of glutathionein-S-transferase (GST) in Escherichia coli. After the GST fusion proteins had been purified by glutathione-Sepharose affinity chromatography column and digested with enterokinase, the metallothionein was purified with gel filtration and analyzed for their biochemical properties. Recombinant MTs were reconstituted with Cd, Cu, and Zn, and kinetic studies of the reactions with electrophilic disulphide, DTNB, were investigated to explore the metal binding ability. It is reveal that the Cd-MT and Zn-Mt react with DTNB biphasically and Zn-MT reacts with DTNB more rapidly and significantly greater observed pseudo-first order rate constant. Cu-MT react monophasic and release metal slowly from metallothionein.