Identification and characterization of a recombinant metallothionein protein from a marine alga, Fucus vesiculosus

Abstract

A cDNA library was constructed from macroalgae adapted to prolonged elevated environmental copper levels. To investigate the possible existence of a metallothionein (MT) gene, the library was screened with degenerate probes designed using plant MT cysteine-rich motifs. A gene was identified (1229 bp) with a putative open reading frame (204 bp) encoding a 67-amino-acid protein exhibiting several characteristic features of MT proteins, including 16 cysteine residues (24%) and only one aromatic residue. Although the protein sequence showed high identity with plant and invertebrate MTs, it contained a unique 'linker' region (14 amino acid residues) between the two putative metal-binding domains which contained no cysteine residues. This extended linker is larger than the tripeptide found in archetypal vertebrate MTs, but does not conform either with the 40-amino-acid linkers commonly found in plant MT sequences. An S-peptide Fucus MT fusion protein expressed in Escherichia coli exhibited a relative molecular mass of approximately 14 kDa. The recombinant fusion bound seven Cd ions, of which 50% were dissociated at pH 4.1. Under anaerobic conditions, the Cd ions were displaced by Cu(I), which associated with the protein at a ratio of 13:1. Laboratory exposure of F. vesiculosus to elevated copper resulted in induction of the MT gene. Thus this paper describes, for the first time, an MT gene identified from macroalgae which is induced by copper exposure and whose encoded protein product binds cadmium and copper.

Characterization and expression of a metallothionein gene in the aquatic fern Azolla filiculoides under heavy metal stress

“…For example, Cu 2+ had either no effect or repressed MT gene expression in V. faba, Mimulus guttatus and soybean (De Miranda et al 1990;Kawashima et al 1991;Foley and Singh 1994). In contrast, MT gene expression was enhanced by Cu 2+ in Arabidopsis (Zhou and Goldsbrough 1995), Fucus (Morris et al 1999) and P. oceanica (Giordani et al 2000).…”

“…The RNA expression of MT genes in other species has been shown to be affected by metal ions (De Miranda et al 1990;Kawashima et al 1991;Foley and Singh 1994;Goldsbrough 1994, 1995;Morris et al 1999;Giordani et al 2000). Exposure of A. filiculoides to elevated concentrations of Cd 2+ , Ni 2+ , Cu 2+ and Zn 2+ resulted in induction of the AzMT2 gene (Fig.…”

“…The relationship between MT expression and metal concentration in different organisms suggests that MTs could be an effective reporter of environmental conditions (Morris et al 1999). The isolation and characterization of MTs from model bioindicator organisms could also contribute to our understanding of the biological response to biomonitoring pollutants in the environment (Morris et al 1999).…”

“…The isolation and characterization of MTs from model bioindicator organisms could also contribute to our understanding of the biological response to biomonitoring pollutants in the environment (Morris et al 1999).…”

The Tropical Brown Alga Lobophora variegata (Lamouroux) Womersley: A Prospective Bioindicator for Ag Contamination in Tropical Coastal Waters

“…The high CFs observed in L. variegata could result from (1) biosorption processes, where the metal in solution binds to the cell walls of the macroalgae (Schiewer and Wong 2000) and/or (2) bioconcentration and sequestration processes, where the metal enters within the cell and strongly binds to macromolecules such as polyphenols, phytochelatins and metallothioneins (Morris et al 1999;Cobbett 2000).…”