posted on 2023-12-04, 15:34authored byAustin
R. Hopiavuori, Shaun M. K. McKinnie
FeII/α-ketoglutarate-dependent
dioxygenases
(Fe/αKG)
make up a large enzyme family that functionalize C–H bonds
on diverse organic substrates. Although Fe/αKG homologues catalyze
an array of chemically useful reactions, hydroxylation typically predominates.
Microalgal DabC uniquely forms a novel C–C bond to construct
the bioactive pyrrolidine ring in domoic acid biosynthesis; however,
we have identified that this kainoid synthase exclusively performs
a stereospecific hydroxylation reaction on its cis substrate regioisomer. Mechanistic and kinetic analyses with native
and alternative substrates identified a 20-fold rate increase in DabC
radical cyclization over β-hydroxylation with no observable
1,5-hydrogen atom transfer. Moreover, this dual activity was conserved
among macroalgal RadC1 and KabC homologues and provided insight into
substrate recognition and reactivity trends. Investigation of this
substrate-dependent chemistry improves our understanding of kainoid
synthases and their biocatalytic application.