|Vandeweghe, Jennifer - USDA-UCB PGEC|
Submitted to: Molecular Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 15, 2001
Publication Date: October 1, 2001
Interpretive Summary: Fission yeast detoxify cadmium by synthesizing phytochelatins, peptides of the structure (gamma GluCys)nGly, which bind cadmium and mediate its sequestration into the vacuole. The fission yeast protein HMT2, a putative sulfide-oxidizing enzyme of the mitochondria, appears to be essential for tolerance to multiple forms of stress, including exposure to cadmium. We found that hmt2- strains are unable to accumulate normal levels of phytochelatins in response to cadmium. Specifically, the high sulfide levels accumulated in the absence of HMT2 function appear to block the activity of phytochelatin synthase, perhaps by precipitating the free cadmium ions required enzyme activity. Although sulfide is required for phytochelatin-mediated metal tolerance, aberrantly high sulfide levels are sufficient to inhibit this pathway. Thus, precise regulation of sulfur metabolism, mediated in part by HMT2, is essential for metal tolerance in fission yeast.
Technical Abstract: This article describes the role of a mitochondrial sulfide-oxidizing enzyme, HMT2, in the biosynthesis of metal binding phytochelatin peptides. The biosynthesis of phytochelatins requires metal-cofactors for the phytochelatin synthase enzyme. During metal stress, sulfide levels rise. In the absence of HMT2, an anomalously high sulfide concentration precipitates the free cadmium ions required for the enzymatic activity of phytochelatin synthase, thereby prevents high level synthesis of phytochelatin peptides.