Reaction: dAMP + S-adenosyl-L-methionine = 4'-phospho-dehydrooxetanocin + 5'-deoxyadenosine + L-methionine (overall reaction)
(1a) S-adenosyl-L-methionine + reduced acceptor = 5'-deoxyadenosin-5'-yl radical + L-methionine + acceptor
(1b) 5'-deoxyadenosin-5'-yl radical + dAMP + acceptor = 4'-phospho-dehydrooxetanocin + 5'-deoxyadenosine + reduced acceptor
Glossary: oxetanocin A = [(2S,3R,4R)-4-(6-amino-9H-purin-9-yl)oxetane-2,3-diyl]dimethanol
Other name(s): oxsB (gene name)
Systematic name: dAMP isomerase (4'-phospho-dehydrooxetanocin-forming)
Comments: The enzyme is a B12-dependent radical SAM (AdoMet) enzyme involved in the biosynthesis of oxetanocin A. The enzyme catalyses an oxidative ring contraction, forming an oxetane aldehyde. The reaction requires S-adenosyl-L-methionine, a cobalamin cofactor, and a reductant (the reductant does not show in the overall reaction because it is being restored during the cycle). The reaction is initiated by formation of 5'-deoxyadenosin-5'-yl radical, which then abstracts a hydrogen atom from C2'. The enzyme is also able to catalyse the radical mediated, stereoselective C2'-methylation of dAMP.
Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc, CAS registry number:
References:
1. Bridwell-Rabb, J., Zhong, A., Sun, H.G., Drennan, C.L. and Liu, H.W. A B12-dependent radical SAM enzyme involved in oxetanocin A biosynthesis. Nature 544 (2017) 322-326. [PMID: 28346939]
2. Lee, Y.H., Yeh, Y.C., Fan, P.H., Zhong, A., Ruszczycky, M.W. and Liu, H.W. Changing Fates of the Substrate Radicals Generated in the Active Sites of the B12-Dependent Radical SAM Enzymes OxsB and AlsB. J. Am. Chem. Soc. 145 (2023) 3656-3664. [PMID: 36719327]