Sheila S. David

Professor

 

Tel: (530) 752-4280

Fax: (530) 752-8995

 

Email:  david@chem.ucdavis.edu

 

Chemical Biology/Bioinorganic and Bioorganic Chemistry

 

B.A. Saint Olaf College, 1984

Ph.D. University of Minnesota, 1989

NIH Postdoctoral Fellow, California Institute of Technology, 1990-1992

 

Appointed to Faculty at UC, Davis, 2006

 

Research Interests

 

DNA Repair, Molecular Mechanisms of Cancer, Nucleic Acid Chemistry and Enzymology, Iron-Sulfur Proteins

 

We use chemical approaches to investigate the fascinating area of DNA repair.  Damage to DNA can result in deleterious outcomes, such as cancer and aging; fortunately, most DNA damage is repaired by DNA repair enzymes (Figure 1)! Our laboratory focuses on the repair of damaged DNA bases which is mediated by the process of base excision repair.  The key enzymes in this pathway are the damage-specific DNA glycosylases that search through the vast amount of normal DNA to find subtle potentially mutagenic base modifications.  Our goals are to understand the molecular details associated with the recognition and repair of DNA damage, and how these features impact mutagenesis and carcinogenesis. 

As chemical biologists interested in DNA repair, we use a variety of approaches and put them together in revealing ways.  The tools of enzymology are used to study the enzyme and its interactions with DNA substrates.  Synthetic techniques are used to synthesize modified DNA substrates to test hypotheses about mechanism, as well as prepare analogues that are resistant to the action of the enzymes.  Bioinorganic approaches are used to manipulate and evaluate the metal sites that are present in most of these enzymes.  Biophysical techniques are used to characterize the protein-DNA complex.  The tools of cell biology and molecular biology are used to manipulate and evaluate “repair” in cells.  Taken together this work makes important connections between the molecular insight derived from our in vitro studies, and how these features impact repair in cells.  Ultimately this will reveal the critical features of the DNA repair process that prevents deleterious mutations leading to cancer, and how these processes may be manipulated for beneficial therapeutic purposes.

 

Main Projects in the Laboratory:

 

1)      Recognition of Damaged DNA by MutY and the Role of MUTYH Variants in Colorectal Cancer:

Oxidative damage to DNA has been implicated as an important causative agent in cancer.  Oxidation of guanine leads to the formation of OG (where OG = 7,8-dihydro-8-oxoguanine) which promotes misincorporation of A during DNA replication to form OG:A base-pairs.  In E. coli, two enzymes prevent mutations caused by OG; the Fpg protein removes OG from OG:C base pairs, while the MutY enzyme removes adenine from OG:A base pairs.  Once the damaged or inappropriate bases are removed, they are replaced with the normal undamaged bases.  Our previous work on delineating the basic properties of the bacterial MutY was important for subsequent work that we participated in that linked defective OG:A repair by the human homologue of MutY (MUTYH) and colorectal cancer (Figure 2).   Our present goals on this project are: (1) To understand how MutY locates OG:A mismatches (2) To elucidate the properties of MUTYH variants that are found in colorectal cancer (3)  To develop new approaches for evaluating the repair activity of MutY/MUTYH that may be useful for diagnostic purposes  (4) To develop novel inhibitors of MutY and MUTYH

 

2)  The Role of [4Fe-4S] Clusters in Base Excision Repair Enzymes

An unusual feature of many of the base excision repair glycosylases (such as MutY/MYH) is the presence of a [4Fe-4S] cluster.  This cluster plays an important role in mediating damage recognition, and recent work also indicates a role for electron-transfer chemistry in the sensing and repair of DNA damage.  Along this line, we have recently also begun to investigate a unique class of [4Fe-4S] cluster containing uracil-DNA glycosylases, that are structurally distinct from MutY, but may use the metal cofactor in an analogous fashion. Our goals in this aspect of work is to determine how the [4Fe-4S] cluster may aid or regulate the ability of these enzymes to find and repair damaged DNA bases.

 

3) Beyond OG

We are also examining the repair by a variety of different enzymes of other oxidized guanine lesions, including primarily spiroiminodihydantoin and guanidinohydantoin (in collaboration with Prof. Cynthia Burrows (Utah)). These two lesions are highly mutagenic and repair may be contributing to the mutagenicity and toxicity afforded by these lesions.  Thus, using similar approaches as we have developed with MutY, we are revealing the molecular features associated with the recognition and repair of these lesions, and how this is associated with the mutagenesis caused by these lesions.

             

 

Recent Representative Publications

 

"An Electron Trap for DNA-bound Repair Enzymes:  A Strategy for DNA-mediated Signaling," Yavin, E., Stemp, E.D.A., O’Shea, V.L., David, S. S., Barton, J.K., Proc. Natl. Acad. Sci, USA,  2006, 103, 3610-3614.

 

"Insight into the Role of Tyrosine 82 and Glycine 253 in the Escherichia coli Adenine Glycosylase MutY, " Livingston, A.L., Kundu, S., Pozzi, M.H., Anderson, D.W., David, S. S., Biochemistry,  2005, 44, 14179-14190.

 

"A Role for Iron-Sulfur Clusters in DNA Repair,” Lukianova, O.A., David, S. S., Curr. Op. Chem. Biol., 2005, 9, 145-151

 

"Protein-DNA Charge Transport:  Redox Activation of a DNA Repair Protein by Guanine Radical, “ Yavin, E.,  Boal, A. K., Stemp,  E. D.A., Boon, E.M., Livingston, A.L., O’Shea, V.L., David, S.S., Barton, J.K., Proc. Natl. Acad. Sci. USA, 2005, 102, 3552-3557

 

"Insight into the functional consequences of hMYH variants associated with colorectal cancer: Distinct differences in the adenine glycosylase activity and the response to AP endonucleases of Y150C and G365D murine MYH," Pope, M.A., Chmiel, N.H., David, S.S., DNA Repair, 2005, 4, 315-325. 38.

 

"A Residue in MutY Important for Catalysis Identified by Photocross-Linking and Mass Spectrometry, " Chepanoske, C. L., Lukianova, O. A., Lombard, M., Golinelli-Cohen, M.-P., David, S. S., Biochemistry, 2004, 43, 651-662

 

"Probing the Requirements for Recognition and Catalysis in Fpg and MutY With Nonpolar Adenine Isosteres, " Francis, A. W., Helquist, S. A., Kool, E. T., David, S. S., J. Am. Chem. Soc, 2003, 125, 16235-16242.

 

"Recognition and Removal of Oxidized Guanines in Duplex DNA by the Base Excision Repair Enzymes hOGG1, yOGG1 and yOGG2, " Leipold, M. D., Workman, H., Muller, J.G., Burrows, C. J., David, S. S., Biochemistry, 2003, 42, 11373-1138129, "Escherichia coli MutY and Fpg Utilize a Processive Mechanism for Target Location,” Francis, A. W. and David, S. S., Biochemistry, 2003, 42, 801-810.

 

"Inherited variants of hMYH associated with colorectal cancer exhibit a compromised ability to recognize and repair A:OG (7,8-dihydro-8-oxo-2’-deoxyguanosine) mismatches in DNA,” Chmiel, N.H.; Livingston, A.L.; David, S.S., Journal of Molecular Biology, 2003, 327, 431-443.

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