Ashok S. Bhagwat Title Professor Division Biochemistry Education B.Sc., University of Bombay, 1972 M.Sc. Indian Institute of Technology, 1974 Ph.D., Pennsylvania State University, 1982 Postdoctoral Fellow, Cold Spring Harbor Laboratory, 1982-1987 Office Chem 443 Phone (313)577-2549 E-Mail

The research in our group is focused on elucidating cellular mechanisms that promote or prevent mutations. The cellular factors that increase mutagenesis include generation of reactive chemical species, methylation of DNA, transcription and human enzymes that damage DNA. Counteracting these potentially hazardous processes are proteins that protect DNA against damage or repair DNA that has been damaged. It is important to understand the interplay between these opposing forces to explain diverse phenomena such as how antibodies are altered to improve recognition of infectious agents, what causes genetic diseases including cancer and how hyperthermophiles survive at temperatures near 100°C. Specific projects include:

The role of AID in antibody maturation: When a foreign agent infects humans, the antibody genes are altered through mutational and recombination processes so that the antibodies will better fit the infecting antigens. This process requires the enzyme activation-induced deaminase (AID), which converts cytosines in DNA to uracil. We are studying the role of this enzyme in causing mutations and DNA strand breaks using biochemical, genetic and bioinformatics tools. Human patients with hyperIgM (HIGM) syndrome often carry mutations in this gene and the location of known HIGM mutations in the structural model for AID is shown (SHMsomatic hypermutation; CSR- class-switch recombination).

Enzymatic dealkylation of DNA: Alkylation of DNA occurs due to the action of cellular or external chemicals. Enzymes related to E. coli AlkB reverse this modification. Two functional human homologs of this enzyme are known and we are studying the biochemistry of five other homologs discovered through a careful search of the human genome.

Transcription-induced mutations: Transcription requires opening of the chromatin and a temporary separation of DNA strands. Both these events expose DNA bases and are known to increase chemical damage. We are studying the effects of different classes of chemical agents on DNA undergoing transcription, and the resulting mutations.

Protection of DNA by proteins: Cellular DNA is wrapped around proteins and this is widely thought to protect it from damage. However, little information is currently available as to which proteins protect DNA and which may sensitize it to damage. We are conducting a systematic study of proteins from hyperthermophiles for their ability to protect or sensitize DNA.

Carpenter, M., Divvela, P., Pingoud, V., Bujnicki, J.M. and Bhagwat, A.S. (2006) “Sequencedependent Enhancement of Hydrolytic Deamination of Cytosines in DNA by the Restriction Enzyme PspGI,” Nucleic Acids Res, in press.

Samaranayake, M., Bujnicki, J.M., Carpenter, M. and Bhagwat, A.S. (2006) Evaluation of molecular models for the affinity maturation of antibodies: roles of cytosine deamination by AID and DNA repair. Chem Rev, 106, 700-719.

Klapacz, J. and Bhagwat, A.S. (2005) “Transcription promotes guanine to thymine mutations in the non-transcribed strand of an Escherichia coli gene,” DNA Repair (Amst), 4, 806-813.

Bhagwat, A.S. (2004) DNA-cytosine deaminases: from antibody maturation to antiviral defense. DNA Repair (Amst), 3, 85-89.

Sohail, A., Klapacz, J., Samaranayake, M., Ullah, A. and Bhagwat, A.S. (2003), “Human activation- induced cytidine deaminase causes transcription- dependent, strand-biased C to U deaminations,”Nucleic Acids Res, 31, 2990- 2994.