The Mechanism of Cyclobutylpyrimidine Dimer Repair by Photoinduced Electron Transfer in DNA Photolyase: Protein and Model Studies

Temple University, Philadelphia PA

Investigators

Abstract

Stanley MCB 9982532 Many organisms have developed DNA repair mechanisms based on photo-induced ultrafast electron transfer from a flavoprotein, called DNA photolyase, to the tightly bound cyclobutylpyrimidine dimer (CPD) lesion. The objective of this research is to elucidate the detailed kinetics and dynamics of the electron transfer and dimer splitting reactions of the photolyase-CPD complex, using near-UV/UV femtosecond absorption spectroscopy. An analysis of these experiments will show whether the CPD is repaired by a concerted or sequential mechanism and what intermediates are involved. Flavin-DNA model systems will be synthesized to isolate and highlight various kinetic details of the enzymatic reaction, including the role of the protein in the repair. Fluorescent labeling technology will be used to gain real-time information on the structural changes that accompany the CPD splitting reaction. Ultraviolet radiation is capable of crosslinking adjacent nucleic acid bases in DNA, leading to mutation and cell death. The most common and lethal DNA photo-lesion is the cyclobutylpyrimidine dimer (CPD). In response to these lesions many organisms use flavoproteins to repair the damaged DNA. These proteins are called photolyases and are unusual in that they require visible light to undo the damage wrought by the mutagenic UV radiation. Upon absorption of visible light the repair process is complete within 2 nanoseconds. This research is aimed at understanding the molecular mechanism behind the light-driven repair reaction.