title: Mechanistic Insights into the Radical S-adenosyl-l-methionine Enzyme NosL From a Substrate Analogue and the Shunt Products.
abstract: The radical S-adenosyl-l-methionine (SAM) enzyme NosL catalyzes the transformation of l-tryptophan into 3-methyl-2-indolic acid (MIA), which is a key intermediate in the biosynthesis of a clinically interesting antibiotic nosiheptide. NosL catalysis was investigated by using the substrate analogue 2-methyl-3-(indol-3-yl)propanoic acid (MIPA), which can be converted into MIA by NosL. Biochemical assays with different MIPA isotopomers in D2 O and H2 O unambiguously indicated that the 5'-deoxyadenosyl (dAdo)-radical-mediated hydrogen abstraction is from the amino group of l-tryptophan and not a protein residue. Surprisingly, the dAdo-radical-mediated hydrogen abstraction occurs at two different sites of MIPA, thereby partitioning the substrate into different reaction pathways. Together with identification of an α,β-unsaturated ketone shunt product, our study provides valuable mechanistic insight into NosL catalysis and highlights the remarkable catalytic flexibility of radical SAM enzymes.
authors.affiliation: Department of Chemistry, Fudan University, Shanghai, 200433, China.
authors.forename: Xinjian
authors.initials: X
authors.lastname: Ji
authors.affiliation: Department of Chemistry, Fudan University, Shanghai, 200433, China.
authors.forename: Yongzhen
authors.initials: Y
authors.lastname: Li
authors.affiliation: Department of Chemistry, Fudan University, Shanghai, 200433, China.|Key Laboratory of Extreme Environmental Microbial Resources and Engineering, Gansu Province, Lanzhou, 730000, China.
authors.forename: Youli
authors.initials: Y
authors.lastname: Jia
authors.affiliation: Department of Chemistry, Fudan University, Shanghai, 200433, China.|Key Laboratory of Extreme Environmental Microbial Resources and Engineering, Gansu Province, Lanzhou, 730000, China.
authors.forename: Wei
authors.initials: W
authors.lastname: Ding
authors.affiliation: Department of Chemistry, Fudan University, Shanghai, 200433, China. qizhang@sioc.ac.cn.
authors.forename: Qi
authors.identifier: http://orcid.org/0000-0002-8135-2221
authors.initials: Q
authors.lastname: Zhang
mesh_terms: D002853:Chromatography, Liquid; D013058:Mass Spectrometry; D012436:S-Adenosylmethionine / Q000378:metabolism*; D013379:Substrate Specificity
chemical_list: D012436:S-Adenosylmethionine
keywords: biosynthesis; carbon-chain rearrangement; natural products; radical addition; thiopeptides