Saturday, February 18, 2012
Exhibit Hall A-B1 (VCC West Building)
Thymine dimers are the most common type of DNA damage caused by UV radiation. Natural Photolyase enzymes can repair thymine dimers with the help of light of 350-450 nm wavelength, which it harvests with different bound chromophores. We have reported a deoxyribozyme (DNAzyme), UV1C, that catalyzes the repair of cyclobutane thymine dimers with the help of light of 300-310 nm wavelength, again without needing any cofactors. While most DNA absorbs very little light at and above 300nm, UV1C shows maximum rate enhancement at 305 nm irradiation. The catalytic core of the UV1C DNAzyme contains a parallel stranded G-quadruplex which we believe functions as an “antenna” for >300nm light. We have recently attempted to “tune the antenna” of UV1C so that it is able to repair thymine dimers with longer wavelengths, and ultimately visible light. The guanine base analog 6-Methylisoxanthopterin (6MI) is also capable of participating in the G-quartet structure of the DNAzymze, but has an absorbance maximum at 340nm. By systematically replacing the guanine bases in the active site with 6MI, we have found mutants of UV1C that are active with longer wavelength light. The different rates of repair of the different mutants also provides valuable information about which specific guanines within the DNAzyme participate directly in catalysis.