Yang, LinlinNelson, Renae S.Benjdia, AlhosnaLin, GengjieTelser, JoshuaStoll, StefanSchlichting, IlmeLi, Lei2025-05-122025-05-122013Yang L, Nelson RS, Benjdia A, et al. A radical transfer pathway in spore photoproduct lyase [published correction appears in Biochemistry. 2013 Jul 16;52(28):4869]. Biochemistry. 2013;52(18):3041-3050. doi:10.1021/bi3016247https://hdl.handle.net/1805/47936Spore 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.en-USPublisher PolicyCrystallizationCatalysisMutationProteinsArticle