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Multisite Prenylation of 4‑Substituted Tryptophans by Dimethylallyltryptophan Synthase
journal contribution
posted on 2013-02-06, 00:00 authored by Jeffrey
D. Rudolf, Hong Wang, C. Dale PoulterThe aromatic prenyltransferase dimethylallyltryptophan
synthase
in Claviceps purpurea catalyzes the
normal prenylation of tryptophan at C4 of the indole nucleus in the
first committed step of ergot alkaloid biosynthesis. 4-Methyltryptophan
is a competitive inhibitor of the enzyme that has been used in kinetic
studies. Upon investigation of background activity during incubations
of 4-methyltryptophan with dimethylallyl diphosphate, we found that
the analogue was an alternate substrate, which gave four products.
The structures of three of these compounds were established by 1H NMR and 2D NMR studies and revealed that dimethylallyltryptophan
synthase catalyzed both normal and reverse prenylation at C3 of the
indole ring and normal prenylation of N1. Similarly, 4-methoxytryptophan
was an alternate substrate, giving normal prenylation at C5 as the
major product. 4-Aminotryptophan, another alternate substrate, gave
normal prenylation at C5 and C7. The ability of dimethylallyltryptophan
synthase to prenylate at five different sites on the indole nucleus,
with normal and reverse prenylation at one of the sites, is consistent
with a dissociative electrophilic alkylation of the indole ring, where
orientation of the substrates within the active site and substituent
electronic effects determine the position and type of prenylation.
These results suggest a common mechanism for prenylation of tryptophan
by all of the members of the structurally related dimethylallyltryptophan
synthase family.