Donald Plocke, S.J.
associate professor of biology
Ph.D., Massachusetts Institute of Technology
Fields of Interest
Molecular biology; structure and function of Class III Metallothioneins; metal ions as regulators in microbial systems; metal ion detoxification mechanisms.
My research interests have included the biological roles of metal ions such as zinc and iron as well as the mechanisms for protection against the toxic effects of metals such as cadmium and copper, using the fission yeast Schizosaccharomyces pombe as a model system for eukaryotic cells. Recent studies have examined mechanisms for protection against copper and cadmium. The properties of metal-binding peptides known as Class III metallothioneins, as well as the conditions for their synthesis, have been the object of several studies.
Work on copper resistance has involved the isolation of a copper-resistant strain of S. pombe, which, unlike S. cerevisiae, does not contain a gene for a Class II metallothionein that accounts for copper resistance in the latter organism. Rather, the resistance trait in S. pombe results from a single recessive chromosomal mutation that appears to affect the properties of the cytoplasmic membrane with the consequence that entry of copper into the cell is inhibited.
Studies involving resistance to cadmium ions have focused on the synthesis of Class III metallothioneins (sometimes called phytochelatins) that have the overall structure [(gammaGlu-Cys)nGly]. These peptides, present in higher plants, occur in S. pombe as well, and their synthesis is stimulated in response to a variety of metal ions, cadmium being the most effective. Peptide synthesis is catalyzed by the constitutive enzyme gammaGlu-Cys dipeptidyl transpeptidase (phytochelatin synthase), that uses glutathione (gammaGlu-Cys-Gly) as an initial substrate. Complexes are formed with metal ions and several peptide molecules, often of heterogeneous lengths, frequently containing inorganic "labile" sulfide as well. Our work has focused on delineation of the stoichiometries and structures of the complexes formed with cadmium and zinc, as well as the conditions required for their formation and their possible biological functions in addition to a likely detoxifying role.
Plocke, D.J., and Lauro, M. M. 1999. Synthesis and properties of Class III metallothioneins of S. pombe in response to cadmium and zinc. In Metallothionein IV (C. Klaassen, ed.) Basel: Birkhäuser Verlag, 195–199.
Plocke, D.J., and Kägi, J.H. 1992. Spectral characteristics of cadmium-containing phytochelatin complexes isolated from Schizosaccharomyces pombe. European Journal of Biochemistry 207: 201–205 (link to PubMed abstract).
Whiteside, S.G., and Plocke, D.J. 1992. Selection and characterization of a copper-resistant subpopulation of Schizosaccharomyces pombe. Journal of General Microbiology 138: 2417–2423.
Plocke, D.J. 1991. Cadmium-binding peptide complexes from Schizosaccharomyces pombe. Methods in Enzymology 205: 603–610 (link to PubMed abstract).
Whiteside, S.G., and Plocke, D.J. 1988. Identification and isolation of core histones from Schizosaccharomyces pombe. FEBS Letters 226: 250–254 (link to PubMed abstract).