Cadmium-inducible BgMT2, a type 2 metallothionein gene from mangrove species (Bruguiera gymnorrhiza), its encoding protein shows metal-binding ability

Metallothioneins (MTs) are a family of low-molecular-weight Cys-rich proteins and are thought to play possible role in metal metabolism or detoxification. To shed light on the role of type 2 MT in Bruguiera gymnorrhiza (BgMT2) under heavy metal stress, B. gymnorrhiza seedlings were exposed to different concentrations of CdCl2 (2 μM, 10 μM, 20 μM or 40 μM) for 3, 7 and 11 d. Real-time quantitative PCR analysis demonstrated that BgMT2 gene transcripts in leaves of B. gymnorrhiza increased in all Cd concentrations and exposure durations. BgMT2 was overexpressed in Escherichia coli BL21 (DE3) as a fusion protein (GST-BgMT2), and bacteria expressing the fusion protein had higher tolerance to Zn, Cu, Pb and Cd than control cells. Moreover, by analysis of metal-binding properties of GST-BgMT2 fusion protein, the expression of BgMT2 endowed resistance in E. coli to Zn, Cu, Pb and Cd by BgMT2 protein sequestering the four metals. Taken together, these data suggest that BgMT2 gene plays an important role in resistance to heavy metals.

Research highlights
► A real-time quantitative PCR protocol was developed to directly evaluate mangrove metallothionein gene expression.
► Cadmium could induce mangrove metallothionein gene expression
► Mangrove metallothionein gene was overexpressing in Escherichia coli.
► Mangrove metallothionein could enhance E. coli tolerance to heavy metals by chelating them.