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The Enzyme-Mediated Direct Reversal of a Dithymine Photoproduct in Germinating Endospores

1 and 1,2,*
Department of Chemistry and Chemical Biology, Indiana University-Purdue University Indianapolis (IUPUI), 402 N Blackford Street, Indianapolis, IN 46202, USA
Department of Biochemistry and Molecular Biology, Indiana University School of Medicine (IUSM), 635 Barnhill Drive, Indianapolis, IN 46202, USA
Author to whom correspondence should be addressed.
Int. J. Mol. Sci. 2013, 14(7), 13137-13153;
Received: 2 May 2013 / Revised: 4 June 2013 / Accepted: 7 June 2013 / Published: 25 June 2013
(This article belongs to the Special Issue Molecular Cut and Paste)
PDF [632 KB, uploaded 19 June 2014]


Spore photoproduct lyase (SPL) repairs a special thymine dimer, 5-thyminyl-5,6-dihydrothymine, which is commonly called spore photoproduct, or SP, in germinating endospores. SP is the exclusive DNA photo-damaging product found in endospores; its generation and swift repair by SPL are responsible for the spores’ extremely high UV resistance. Early in vivo studies suggested that SPL utilizes a direct reversal strategy to repair SP in the absence of light. Recently, it has been established that SPL belongs to the radical S-adenosylmethionine (SAM) superfamily. The enzymes in this superfamily utilize a tri-cysteine CXXXCXXC motif to bind a [4Fe-4S] cluster. The cluster provides an electron to the S-adenosylmethionine (SAM) to reductively cleave its C5'-S bond, generating a reactive 5'-deoxyadenosyl (5'-dA) radical. This 5'-dA radical abstracts the proR hydrogen atom from the C6 carbon of SP to initiate the repair process; the resulting SP radical subsequently fragments to generate a putative thymine methyl radical, which accepts a back-donated H atom to yield the repaired TpT. The H atom donor is suggested to be a conserved cysteine141 in B. subtilis SPL; the resulting thiyl radical likely interacts with a neighboring tyrosine99 before oxidizing the 5'-dA to 5'-dA radical and, subsequently, regenerating SAM. These findings suggest SPL to be the first enzyme in the large radical SAM superfamily (>44,000 members) to utilize a radical transfer pathway for catalysis; its study should shed light on the mechanistic understanding of the SAM regeneration process in other members of the superfamily. View Full-Text
Keywords: thymine dimer; DNA damage; DNA damage repair; radical; transfer pathway thymine dimer; DNA damage; DNA damage repair; radical; transfer pathway
This is an open access article distributed under the Creative Commons Attribution License (CC BY 3.0).

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Yang, L.; Li, L. The Enzyme-Mediated Direct Reversal of a Dithymine Photoproduct in Germinating Endospores. Int. J. Mol. Sci. 2013, 14, 13137-13153.

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