Poster abstracts

Poster number 32 submitted by Yukti Aggarwal

Effect of temperature on DNA photolyase dynamics

Yukti Aggarwal (Biophysics)

Abstract:
DNA Photolyase is a family of enzymes that repairs DNA lesions that are known to have mutagenic, carcinogenic and lethal effects on organisms. The action mechanism of these enzymes involves ‘photo-reactivation’ via visible light and their substrates are UV-induced pyrimidine dimers in damaged DNA, such as cyclobutane type pyrimidine dimers (CPD) and 6-4 photoproduct (6-4 PP). Although no longer present in mammalian system to repair DNA, humans have analogues called ‘Cryptochromes’ that mediate circadian rhythms. These enzymes contain FAD (Flavin Adenine Dinonucleotide), which upon photoreduction to FADH- either via direct absorption of photon or resonance energy transfer from second chromophore MTHF (Methenyltetrahydrofolate), transfers electron directly to substrate for catalytic repair of dimers followed by regeneration of reduced enzyme. The photochemical reactions pertaining to catalytic steps have been under intense investigation for past several years and still several aspects of it needs clarification. One aspect is the temperature dependence of enzyme dynamics. This study of process of electron transfer and lifetime of catalytic cofactor FADH- in 6-4 Photolyase has been carried out using Time-Correlated Single Photon Counting (TCSPC) over the temperature range from 77K to 293K to unravel dynamics at sub-nano and pico second time scale under present study. The kinetics of electron transfer has been found to be non-exponential and can still be seen at 77K. Different protein mutants would be studied and other than using TCSPC, experiments will be carried out using Ultrafast Spectroscopy to understand role of protein in electron transfer dynamics.

Keywords: DNA photolyase, TCSPC, electron transfer