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Stereochemistry in the Reaction of the myo-Inositol Phosphate Synthase Ortholog Ari2 during Aristeromycin Biosynthesis
journal contribution
posted on 2019-12-13, 20:35 authored by Fumitaka Kudo, Takeshi Tsunoda, Kaito Yamaguchi, Akimasa Miyanaga, Tadashi EguchiThe myo-inositol-1-phosphate synthase
(MIPS) ortholog
Ari2, which is encoded in the aristeromycin biosynthetic gene cluster,
catalyzes the formation of five-membered cyclitol phosphate using d-fructose 6-phosphate (F6P) as a substrate. To understand the
stereochemistry during the Ari2 reaction in vivo,
we carried out feeding experiments with (6S)-d-[6-2H1]- and (6R)-d-[6-2H1]glucose in the aristeromycin-producing
strain Streptomyces citricolor. We observed retention
of the 2H atom of (6S)-d-[6-2H1]glucose and no incorporation of the 2H atom from (6R)-d-[6-2H1]glucose in aristeromycin. This indicates that Ari2 abstracts
the pro-R proton at C6 of F6P after oxidation of
C5-OH by nicotinamide adenine dinucleotide (NAD+) to generate
the enolate intermediate, which then attacks the C2 ketone to form
the C–C bond via aldol-type condensation. The reaction of Ari2
with (6S)-d-[6-2H1]- and (6R)-d-[6-2H1]F6P in
vitro exhibited identical stereochemistry compared with that
observed during the feeding experiments. Furthermore, analysis of
the crystal structure of Ari2, including NAD+ as a ligand,
revealed the active site of Ari2 to be similar to that of MIPS of Mycobacterium tuberculosis, supporting the similarity of
the reaction mechanisms of Ari2 and MIPS.
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2 H atomNADfive-membered cyclitol phosphateInositol Phosphate Synthase Ortholog Ari 2aristeromycin-producing strain Streptomyces citricoloraristeromycin biosynthetic gene clusternicotinamide adenine dinucleotideAri 2inositol -1-phosphate synthaseAri 2 reactionF 6PAri 2 abstractsglucose5-OHMIPSd-fructose 6- phosphateC 2 ketone
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