Heterologous Expression of a rice metallthionein isoform type 2 (OsMTI-2b) in Escherichia coli

Metallothioneins (MTs) are low molecular weight, Cys-rich proteins that are able to bind metals through the thiol groups of their Cys residues. Plants have multiple MT isoforms which are divided in 4 types based on distribution of Cys residues. In the present work, the gene encoding OsMTI-2b, a rice MT type 2 (Oryza sativa), was cloned into pET41a vector. The resulting construct was transformed into Escherichia coli strain Rosetta (DE3). Following the induction with Isopropyl β-D-1-thiogalactopyranoside the OsMTI-2b was expressed as carboxyl-terminal extensions of glutathione-S-transferase (GST). As compared with control, the E. coli cells expressing GST-OsMTI-2b showed increased tolerance against metals Ni, Cd, Pb and Zn. Furthermore in the medium of cells expressing GST-OsMTI-2b the concentration of Pb2, Cd2, Ni2, Zn2 and Cu2痧⭹꬞ 15.85±0.7, 13.07±0.8, 11.8±0.8, 14.51±0.75 and 7.47±0.6 ppm, respectively. In comparison, the concentration of these metals did not change in the medium of control strain.