Metal-Specific Synthesis of Two Metallothioneins and γ -glutamyl Peptides in Candida glabrata

Cellular resistance to heavy metal cytotoxicity in most species is mediated by the binding of metal ions either to a cysteine-rich polypeptide in the metallothionein family or to short cysteine-containing gamma-glutamyl peptides. One of these metal binding systems has been found in most organisms studied. However, the yeast Candida (Torulopsis) glabrata expresses both metallothionein and the gamma-glutamyl peptides for metal detoxification, and each system is regulated in a metal-specific manner. Exposure of C. glabrata to copper salts stimulates formation of two metallothionein-like polypeptides with a cysteine content of 30 mol% and the repeated sequence Cys-Xaa-Cys. The cells synthesize gamma-glutamyl peptides upon exposure to cadmium salts. Penta- and tetrapeptides that form a cadmium-thiolate cluster in a peptide oligomer containing labile sulfur are synthesized.