Aminofutalosine Synthase (MqnE): A New Catalytic Motif in Radical SAM Enzymology

Menaquinone Biosynthesis: The Mechanism of 5,8-Dihydroxy-2-naphthoate Synthase (MqnD)

“…Labeled SAM was biosynthesized from [U- 13 C]ATP using a previously reported method. 24 This isotopologue of 6 yielded an oxime with the expected 3 Da mass increase (Figure 4C and Figure S42). These data ruled out the oxime of 14 (m/z 268.03) and the oxime of 15 (m/z 268.03) as possible three-carbon fragments and hence eliminated mechanisms A and B.…”

“…We therefore explored the possibility of a chemoenzymatic synthesis of 6 using MqnE, MTAN, and MqnC (Figure A and Figures S1 and S2). Compound 2 can be readily synthesized in large quantities, and recent studies have demonstrated robust enzymatic activity of the radical SAM enzyme MqnE to give 3 . ,, MTAN, a well-studied nucleosidase, can then be employed to generate 5 (Figures S8–S10). , However, the radical SAM enzyme MqnC has low in vitro activity, and this enzyme is therefore the limiting step in the enzymatic synthesis of 6 .…”

Eukaryotic TYW1 Is a Radical SAM Flavoenzyme

“…A key requirement for activation of all RS enzymes is the obligate reduction from the resting +2 state of the Fe–S cluster to the catalytically active +1 oxidation state. Most in vitro studies employ dithionite as a reductant, − though other non-natural reducing systems such as Ti­(III) citrate , and various mediators have also been shown to be effective , in some but not all cases . Since the demonstration that ribonucleotide reductase can be activated by flavodoxin/flavodoxin reductase with NADPH as the electron source, this reducing system (from Escherichia coli ) has also been employed as a proxy for the cellular reducing system. ,,, This has led to the generalization that a flavodoxin-like protein is most likely involved in the activation of RS enzymes in vivo .…”

“…Most in vitro studies employ dithionite as a reductant, − though other non-natural reducing systems such as Ti­(III) citrate , and various mediators have also been shown to be effective , in some but not all cases . Since the demonstration that ribonucleotide reductase can be activated by flavodoxin/flavodoxin reductase with NADPH as the electron source, this reducing system (from Escherichia coli ) has also been employed as a proxy for the cellular reducing system. ,,, This has led to the generalization that a flavodoxin-like protein is most likely involved in the activation of RS enzymes in vivo . It is somewhat remarkable that the E. coli flavodoxin homologue has been successfully used to reconstitute activity in a wide variety of RS enzymes, as there is no reason to expect that the surfaces that drive the interactions between the flavodoxin homologue and RS enzymes are identical .…”

Antibacterial Strategy against H. pylori: Inhibition of the Radical SAM Enzyme MqnE in Menaquinone Biosynthesis

“…22 We have previously reported mechanistic studies on this enzyme with successful trapping of the captodative radical 3 and the aryl radical anion 7 ( Figure 1). 23,24 High throughput screening for inhibitors of radical SAM enzymes is technically demanding because these enzymes are extremely oxygen sensitive and have low turnover. We therefore undertook a mechanism-guided approach for the development of an inhibitor of MqnE.…”