Cloning and Characterization of Metallothionein genes of Suillus Species

Abstract

Metallothioneins are low molecular weight proteins that are rich in cysteine residues and have the ability to bind to various metal ions like (eg: Zn2+, Cu2+). These proteins have been actively involved in the detoxification of heavy metals. They are involved in maintaining the haemostasis of essential traces metals as well as in sequestration of the environmentally toxic metals. The present study is focused on the characterization and evaluation of two MT genes in three Suillus species i.e Suillus sibricus, Suillus himalayensis and Suillus indicus. These two genes (MT1 and MT2) are found to be rich in the cysteine residues and have C-X-C motifs, which are the characterstic feature of metallothionein genes. The expression level of these genes was found to be increases with the increase in the external copper concentration. Heterologous complementation assays in the metal sensitive yeast strains indicated that both MT1 and MT2 genes encode for a polypeptide that provides tolerance against copper, cadmium and zinc. Higher expression level of MT1 and MT2 were observed in the three Suillus species when they were exposed to the different concentration of copper. Moreover there growth was also predicted at different concentration of copper. Thus the data obtained provides the evidence that metallothionien in Suillus species protects them from heavy metal stress.