Spore photoproduct lyase: the known, the controversial, and the unknown - PubMed (original) (raw)

Review

Spore photoproduct lyase: the known, the controversial, and the unknown

Linlin Yang et al. J Biol Chem. 2015.

Abstract

Spore photoproduct lyase (SPL) repairs 5-thyminyl-5,6-dihydrothymine, a thymine dimer that is also called the spore photoproduct (SP), in germinating endospores. SPL is a radical S-adenosylmethionine (SAM) enzyme, utilizing the 5'-deoxyadenosyl radical generated by SAM reductive cleavage reaction to revert SP to two thymine residues. Here we review the current progress in SPL mechanistic studies. Protein radicals are known to be involved in SPL catalysis; however, how these radicals are quenched to close the catalytic cycle is under debate.

Keywords: DNA Repair; DNA-Protein Interaction; Enzyme Catalysis; Enzyme Mechanism; Radiation Biology; Radical; Redox.

© 2015 by The American Society for Biochemistry and Molecular Biology, Inc.

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Figures

FIGURE 1.

FIGURE 1.

The chemical structures of naturally occurring thymine photodimers.

FIGURE 2.

FIGURE 2.

The hypothesized reaction mechanism for SPL (the residues are numbered according to the protein sequence in B. subtilis SPL). This mechanism implies that SPL uses a minimum of four hydrogen atom transfer processes (labeled in blue numbers) in each catalytic cycle. The first two HAT processes are well established, and the last two HAT processes are under debate. SAM is shown to be regenerated at the end of the catalytic cycle, which is also controversial. (The figure is modified with permission from Ref. . Copyright (2013) American Chemical Society.)

FIGURE 3.

FIGURE 3.

Hydrogen atom migration during the SP formation and repair by SPL. A hydrogen atom migrates to the H6pro_S_ position of the formed SP, whereas the H6pro_R_ atom is abstracted to initiate the SP repair process. Therefore, the H6 atom of regenerated 5′-thymine after SPL repair is different from that before SP is formed. This observation provides the rationale for the previous tritium-labeling experiments (18, 26).

FIGURE 4.

FIGURE 4.

The active site of G. thermodenitrificans (Gt) SPL in complex with SP and SAM. Cys-140(Gt), Tyr-96(Gt), and Tyr-98(Gt) equal to Cys-141(Bs), Tyr-97(Bs), and Tyr-99(Bs) in B. subtilis SPL, respectively. The distances (Å) between selected residues, SP, and SAM are indicated by the black numbers near the dashed lines (Protein Data Bank (PDB) code 4FHD).

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