SCIENCE AT THE EDGE SEMINAR

Friday, 29 August 2008 at 11:30am

Room 1400 Biomedical and Physical Sciences Bldg.

Refreshments at 11:15


Speaker: Dr. Dongping Zhong
         Departments of Physics, Chemistry, and Biochemistry
         Programs of Biophysics, Chemical Physics, and Biochemistry
         The Ohio State University

Title:   Ultrafast Enzymatic Catalysis: DNA Repair by Photolyase

Abstract:

Photolyase uses light energy to split ultraviolet-induced cyclobutane
pyrimidine dimers in damaged DNA.  Although this enzyme has been discovered
for about 50 years, the molecular mechanism has never been directly revealed.
Here, we report the direct mapping of entire catalytic processes through
femtosecond synchronization of the enzymatic dynamics with the repair
function.  By integrating physical, chemical and biochemical methods, we
are able to observe the repair processes to be completed within hundreds of
picoseconds through a cyclic electron transfer reaction.  The reactions are
strongly modulated by active-site solvation to achieve maximum repair
efficiency.  These results show that the photocycle of DNA repair by
photolyase is through a radical mechanism and completed on ultrafast time
scales at the dynamic active site with no net electron change in redox
states of the flavin cofactor.