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Expanding the Chemistry of the Class C Radical SAM Methyltransferase NosN by Using an Allyl Analogue of SAM
Author(s) -
Ji Xinjian,
Mandalapu Dhanaraju,
Cheng Jinduo,
Ding Wei,
Zhang Qi
Publication year - 2018
Publication title -
angewandte chemie
Language(s) - English
Resource type - Journals
eISSN - 1521-3757
pISSN - 0044-8249
DOI - 10.1002/ange.201712224
Subject(s) - chemistry , stereochemistry , substrate (aquarium) , radical cyclization , allyl alcohol , enzyme , catalysis , biochemistry , oceanography , geology
The radical S‐adenosylmethionine (SAM) superfamily enzymes cleave SAM reductively to generate a highly reactive 5′‐deoxyadenosyl (dAdo) radical, which initiates remarkably diverse reactions. Unlike most radical SAM enzymes, the class C radical SAM methyltransferase NosN binds two SAMs in the active site, using one SAM to produce a dAdo radical and the second as a methyl donor. Here, we report a mechanistic investigation of NosN in which an allyl analogue of SAM (allyl‐SAM) was used. We show that NosN cleaves allyl‐SAM efficiently and the resulting dAdo radical can be captured by the olefin moieties of allyl‐SAM or 5′‐allylthioadenosine (ATA), the latter being a derivative of allyl‐SAM. Remarkably, we found that NosN produced two distinct sets of products in the presence and absence of the methyl acceptor substrate, thus suggesting substrate‐triggered production of ATA from allyl‐SAM. We also show that NosN produces S‐adenosylhomocysteine from 5′‐thioadenosine and homoserine lactone. These results support the idea that 5′‐methylthioadenosine is the direct methyl donor in NosN reactions, and demonstrate great potential to modulate radical SAM enzymes for novel catalytic activities.