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Mechanistic Insights into the Radical S ‐adenosyl‐ l ‐methionine Enzyme NosL From a Substrate Analogue and the Shunt Products
Author(s) -
Ji Xinjian,
Li Yongzhen,
Jia Youli,
Ding Wei,
Zhang Qi
Publication year - 2016
Publication title -
angewandte chemie international edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.831
H-Index - 550
eISSN - 1521-3773
pISSN - 1433-7851
DOI - 10.1002/anie.201509900
Subject(s) - chemistry , hydrogen atom abstraction , tryptophan , stereochemistry , methionine , residue (chemistry) , enzyme , catalysis , propanoic acid , enzyme catalysis , catalytic cycle , amino acid , radical , biochemistry
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 D 2 O and H 2 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.