Analysis of type 2 metallothionein gene from mangrove species (Kandelia candel)

Metallothioneins are Cys-rich, low-molecular weight, metal-binding proteins. In this paper, we aimed to evaluate the roles of type 2 metallothionein in Kandelia candel (KcMT2) by analyzing its mRNA expression in leaves in response to heavy metals, as well as the metal-binding properties of its protein. The transcriptional response of KcMT2 gene to different heavy metals (Zn, Cu, Pb and Cd) was measured using real-time quantitative PCR. The results showed that the gene was regulated by the four metals tested. Significant increase in the expression of KcMT2 mRNA was also found in response to Zn, Cu, Pb and Cd. To analyze further the possible roles of KcMT2 against heavy metals, it was expressed in Escherichia coli BL21 as a carboxy-terminal extension of glutathione-S-transferase (GST). The E. coli cells expressing GST-KcMT2 fusion protein showed higher growth compared to the control cells under Zn, Cu, Pb or Cd exposure, and the GST-KcMT2 fusion protein had a stronger binding affinity for Zn, Cu, Pb and Cd than GST alone. Results presented here reveal that KcMT2 may play important roles in the heavy metal homeostasis or detoxification.