Dr Ulrike Kappler
Position: UQ Strategic Postdoctoral Research Fellow
Affiliation: University of Queensland, School of Molecular and Microbial Sciences
School of Molecular and Microbial Sciences
University of Queensland
Brisbane QLD 4072
Phone: +61 (07) 33651892
Fax: +61 (07) 33654699
I am interested in bacterial sulfite-oxidizing metalloenzymes, which constitute a large new group of bacterial molybdoenzymes. Sulfite-oxidizing enzymes occur mainly in microorganisms capable of dissimilatory sulfur oxidation such as our model organism, the soil bacterium Starkeya novella.
Molecular basis for the oxidation of sulfite in bacterial sulfite dehydrogenases
We have purified the first confirmed bacterial sulfite dehydrogenase fom Starkeya novella and have shown that it contains heme c and molybdenum. It also is structurally different from the well studied mammalian and avian sulfite oxidases: While having similar catalytic parameters, initial spectroscopic studies have shown that the reaction centre of the bacterial sulfite dehydrogenase is different from that of the sulfite oxidases. Using a variety of biochemical and spectroscopic techniques we are currently trying to elucidate the molecular processes underlying these differences.
To make the enzyme more accessible to e.g. site-directed mutagenesis, a protein expression system that uses Rhodobacter capsulatus as the host has been successfully developed. A crystal structure of the enzyme (collaboration with S Bailey) will aid the understanding of the processes involved and in selecting targets for site-directed mutagenesis.
Diversity and in vivo function of sulfite dehydrogenases
In addition, the in vivo role of the enzyme is being investigated using a proteomics approach to identify components of the relevant sulfur oxidation pathways. Starkeya novella is capable of chemolithotrophic growth on different reduced sulfur compounds but can also grow as a heterotroph. We hope to identify proteins involved in sulfur oxidation by comparing protein maps generated from cells grown under different conditions.
Another area of interest is the diversity of sulfite-oxidizing enzymes. Genome projects have revealed the presence of sulfite-dehydrogenase related genes in various microorganisms and archaea, including some plant and human pathogens. Selected enzymes are being targeted for heterologous expression and further studies.
- Kappler, U., Bennett, B., Rethmeier, J., Schwarz, G., Deutzmann, R., McEwan, A.G. and C. Dahl (2000)
Sulfite: cytochrome c oxidoreductase from Thiobacillus novellus – purification, characterization and molecular biology of a heterodimeric member of the sulfite oxidase family. Journal of Biological Chemistry 275, 13202-13212
- Kappler, U. and C. Dahl (2001) Enzymology and molecular biology of prokaryotic sulfite oxidation FEMS Microbiology Letters 203, 1-9
- Kappler, U. and A.G. McEwan (2002) A system for the heterologous expression of complex redox proteins in Rhodobacter capsulatus: characterization of recombinant sulfite:cytochrome c oxidoreductase from Starkeya novella. FEBS Letters 529, 208-214
- Aguey-Zinsou, K.-F.; Bernhardt, P.V., Kappler, U. and A.G. McEwan (2003) Direct electrochemistry of a bacterial sulfite dehydrogenase J.Am.Chem.Soc. 125, 530-535
- Feng, C.I., Kappler U., Tollin, G. and J.E. Enemark Laser-flash photolysis of a bacterial sulfite dehydrogenase J.Am.Chem.Soc. 125 (2003) 14696 -14697
- Kappler, U., Aguey-Zinsou, K.-F., Hanson, G.R., Bernhardt, P.V. and A.G. McEwan Cytochrome c551 from Starkeya novella – characterization, spectroscopic properties and phylogeny of a diheme protein of the SoxAX family in press, J.Biol.Chem. (2004)
J.E. Enemark (University of Arizona, USA)
Sue Bailey (Daresbury Laboratories, UK)