Complete stereospecific repair of a synthetic dinucleotide spore photoproduct by spore photoproduct lyase |
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Authors: | Sunshine C Silver Tilak Chandra Egidijus Zilinskas Shourjo Ghose William E Broderick Joan B Broderick |
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Institution: | (1) Department of Chemistry and Biochemistry, The Astrobiology Biogeocatalysis Research Center, Montana State University, 103 CBB, Bozeman, MT 59717, USA; |
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Abstract: | Spore photoproduct lyase (SP lyase), a member of the radical S-adenosylmethionine superfamily of enzymes, catalyzes the repair of 5-thyminyl-5,6-dihydrothymine spore photoproduct (SP)],
a type of UV-induced DNA damage unique to bacterial spores. The anaerobic purification and characterization of Clostridium acetobutylicum SP lyase heterologously expressed in Escherichia coli, and its catalytic activity in repairing stereochemically defined synthetic dinucleotide SPs was investigated. The purified
enzyme contains between 2.3 and 3.1 iron atoms per protein. Electron paramagnetic resonance (EPR) spectroscopy reveals an
isotropic signal centered at g = 1.99, characteristic of a 3Fe–4S]+ cluster accounting for 3–4% of the iron in the sample. Upon reduction, a nearly axial signal (g = 2.03, 1.93 and 1.92) characteristic of a 4Fe–4S]+ cluster is observed that accounts for 34–45% of total iron. Addition of S-adenosylmethionine to the reduced enzyme produces a rhombic signal (g = 2.02, 1.93, 1.82) unique to the S-adenosyl-l-methionine complex while decreasing the overall EPR intensity. This reduced enzyme is shown to rapidly and completely repair
the 5R diastereomer of a synthetic dinucleotide SP with a specific activity of 7.1 ± 0.6 nmol min−1 mg−1, whereas no repair was observed for the 5S diastereomer. |
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