Ultrafast dynamics of energy and electron transfer in DNA-photolyase

 
 
 
 

Ultrafast dynamics of energy and electron transfer in DNA-photolyase

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Title: Ultrafast dynamics of energy and electron transfer in DNA-photolyase
Author: Saxena, Chaitanya
Description: One of the detrimental effects of UV radiation on the biosphere is the formation of cyclobutane pyrimidine dimers (Pyr<>Pyr) between two adjacent thymine bases in DNA. Pyr<>Pyr dimers bring DNA repair machinery in the cell to a standstill and may result in mutation or cell death. Photolyase which is a photoenzyme that exists in all three branches of life, harnesses blue or near-UV light energy to cleave the cyclobutane ring of the Pyr<>Pyr and, thus, prevents the harmful effects of UV radiation. Photolyase obtained from E.coli is a monomeric protein with two noncovalently attached cofactors: one is a light-harvesting photoantenna, a pterin molecule in the form of methenyltetrahydrofolate (MTHF), and the other one is the catalytic cofactor, a fully reduced deprotonated flavin molecule (FADH -). In the proposed hypothesis for the catalysis, the enzyme binds a Pyr<>Pyr in DNA, independent of light. The antenna chromophore MTHF harvests UV/blue-light photon, and transfers the excitation energy (dipole-dipole interaction) to FADH -. Excited FADH -*then transfers an electron to the Pyr<>Pyr, which consequently splits the Pyr<>Pyr into two pyrimidines and hence repairs the damaged DNA. The repair cycle ends when the excess electron is transferred from the repaired pyrimidine back to the nascent-formed FADH and regenerates the active FADH -form. The complex mechanism of energy and electron transfer in photolyase enzyme was investigated using state-of-the-art femtosecond laser spectroscopy in this study. The photophysics of FADH -cofactor was also studied in aqueous solution. Dramatic shortening of the excited state lifetime of FADH -in aqueous solution compare to its lifetime in protein environment compelled us to propose that enzyme photolyase modulates photophysical properties of the flavin cofactor to perform the essential biological function of electron transfer to repair damaged DNA.
Permanent Link: http://rave.ohiolink.edu/etdc/view?acc_num=osu1171317950
http://hdl.handle.net/2374.OX/6816
Date: 2007

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