Dr. Bruce L. Martin Assistant Professor e-mail: bmartin@utmem1.utmem.edu Phone: 901-448-4373
B.S. 1981, University of Notre Dame Ph.D. 1987, Iowa State University Postdoctoral 1987-1991, Brown University Research Interests:
Post-translational modifications of enzymes are critical and ubiquitous mechanisms for the control of cellular physiology, particularly those processes involved in signal transduction. Of the different modification reactions which have been identified, protein phosphorylation is arguably the most important in the regulation of these signaling events. Reversible protein phosphorylation- dephosphorylation involves opposing reactions catalyzed by kinases and phosphatases. The primary focus of my lab is understanding the basis for the specificity of protein phosphatases and the regulation of phosphatase activity. A central approach is to define the enzymatic mechanism of phosphatase action to provide direction for the development of novel reagents to use as specific probes of phosphatase function. The calmodulin activated phosphatase, calcineurin, is the model used to study phosphatase action. Calcineurin is a zinc/iron metalloenzyme, but requires exogenous divalent metal for full activity. The enzyme has in vitro activity toward proteins with phosphoserine, phosphothreonine, or phosphotyrosine residues. More significantly for our studies, calcineurin has activity with low molecular weight phosphate esters enabling the systematic study of chemically defined substrates. Using kinetics, spectroscopic techniques, and mutagenesis, we are characterizing the interactions of calcineurin with these essential metals and with substrates at the molecular level.
Little information about the cellular substrate specificity of calcineurin is readily available. I plan to initiate studies to define the cellular substrates using PC12 cells in culture because these cells are readily permeabilized to allow the introduction of specific probes. Using calcineurin and calmodulin antagonists, specific target proteins will be identified and characterized. This system will be used to investigate the biological functions of this specific phosphatase.
These directions of research will merge to provide a model system for testing the developed reagents and answering critical questions about the role of protein dephosphorylation in cell regulation, in particular the role of calcineurin. This system may also serve as a test model for probing calcium and calmodulin regulated signaling events.
Recent Publications:
1. Martin, B.L. (1993) Enzyme Catalyzed Covalent Modification Reactions: An Overview in "Biochemistry LABFAX." Chambers, A., and Rickwood, D., Eds. BIOS ScientificPublishers Ltd. pp. 213, 233-239.
2. Martin, B.L., and Graves, D.J. (1993) Hydrolysis of Trifluoroethyl Phosphate as Evidence that the Serine and Tyrosine Phosphatase Activities of Calcineurin Share the Same Specific-ity Determinant. Biochem. Biophys. Res. Commun. 194, 150-156.
3. Martin, B.L., and Graves, D.J. (1994) Isotope Effects on the Mechanism of Calcineurin Catalysis: Kinetic Solvent Isotope and Isotope Exchange Studies. Biochim. Biophys. Acta 1206, 136-142.
4. Graves, D.J., Martin, B.L., and Wang, J.H. (1994) "Co- and Post- translational Modifications of Proteins: Chemical Principles and Biological Significance." Oxford University Press. 352 pp.