Three metallothionein isoforms and sequestration of intracellular silver in the hyperaccumulator Amanita strobiliformis
Abstract
Metallothioneins (MTs) are cysteine-rich peptides involved in heavy metal tolerance of many eukaryotes. Here, we examined their involvement in intracellular binding of silver (Ag) in the ectomycorrhizal fungus Amanita strobiliformis.
The Ag complexes and their peptide ligands were characterized using chromatography and mass spectrometry. The full-length coding sequences obtained from a cDNA library were used for complementation assays in yeast mutant strains.
Abundance of respective transcripts in A. strobiliformis was measured by quantitative real-time reverse-transcribed polymerase chain reaction (qRT-PCR). Ag-speciation analyses showed that intracellular Ag was in wild-grown fruit bodies and cultured extraradical mycelia of A. strobiliformis sequestered by metallothioneins.
The determined sequence of the peptide facilitated isolation of three cDNA clones, AsMT1a, AsMT1b and AsMT1c. These encode isomorphic MTs consisting of 34 amino acid residues and sharing 82% identity.