title: A radical transfer pathway in spore photoproduct lyase.
abstract: Spore photoproduct lyase (SPL) repairs a covalent UV-induced thymine dimer, spore photoproduct (SP), in germinating endospores and is responsible for the strong UV resistance of endospores. SPL is a radical S-adenosyl-l-methionine (SAM) enzyme, which uses a [4Fe-4S](+) cluster to reduce SAM, generating a catalytic 5'-deoxyadenosyl radical (5'-dA(•)). This in turn abstracts a H atom from SP, generating an SP radical that undergoes β scission to form a repaired 5'-thymine and a 3'-thymine allylic radical. Recent biochemical and structural data suggest that a conserved cysteine donates a H atom to the thymine radical, resulting in a putative thiyl radical. Here we present structural and biochemical data that suggest that two conserved tyrosines are also critical in enzyme catalysis. One [Y99(Bs) in Bacillus subtilis SPL] is downstream of the cysteine, suggesting that SPL uses a novel hydrogen atom transfer (HAT) pathway with a pair of cysteine and tyrosine residues to regenerate SAM. The other tyrosine [Y97(Bs)] has a structural role to facilitate SAM binding; it may also contribute to the SAM regeneration process by interacting with the putative (•)Y99(Bs) and/or 5'-dA(•) intermediates to lower the energy barrier for the second H abstraction step. Our results indicate that SPL is the first member of the radical SAM superfamily (comprising more than 44000 members) to bear a catalytically operating HAT chain.
authors.affiliation: Department of Chemistry and Chemical Biology, Indiana University-Purdue University Indianapolis, Indianapolis, IN 46202, USA.
authors.forename: Linlin
authors.initials: L
authors.lastname: Yang
authors.forename: Renae S
authors.initials: RS
authors.lastname: Nelson
authors.forename: Alhosna
authors.initials: A
authors.lastname: Benjdia
authors.forename: Gengjie
authors.initials: G
authors.lastname: Lin
authors.forename: Joshua
authors.initials: J
authors.lastname: Telser
authors.forename: Stefan
authors.initials: S
authors.lastname: Stoll
authors.forename: Ilme
authors.initials: I
authors.lastname: Schlichting
authors.forename: Lei
authors.initials: L
authors.lastname: Li
mesh_terms: D002384:Catalysis; D002851:Chromatography, High Pressure Liquid; D003460:Crystallization; D007700:Kinetics; D008958:Models, Molecular; D009154:Mutation; D011506:Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D012436:S-Adenosylmethionine / Q000378:metabolism
chemical_list: D011506:Proteins; D012436:S-Adenosylmethionine; C088014:spore photoproduct lyase