A novel l-isoleucine-4'-dioxygenase and l-isoleucine dihydroxylation cascade in Pantoea ananatis.

A unique operon structure has been identified in the genomes of several plant- and insect-associated bacteria. The distinguishing feature of this operon is the presence of tandem hilA and hilB genes encoding dioxygenases belonging to the PF13640 and PF10014 (BsmA) Pfam families, respectively. The genes encoding HilA and HilB from Pantoea ananatis AJ13355 were cloned and expressed in Escherichia coli. The culturing of E. coli cells expressing hilA (E. coli-HilA) or both hilA and hilB (E. coli-HilAB) in the presence of l-isoleucine resulted in the conversion of l-isoleucine into two novel biogenic compounds: l-4'-isoleucine and l-4,4'-dihydroxyisoleucine, respectively. In parallel, two novel enzymatic activities were detected in the crude cell lysates of the E. coli-HilA and E. coli-HilAB strains: l-isoleucine, 2-oxoglutarate: oxygen oxidoreductase (4'-hydroxylating) (HilA) and l-4'-hydroxyisoleucine, 2-oxoglutarate: oxygen oxidoreductase (4-hydroxylating) (HilB), respectively. Two hypotheses regarding the physiological significance of C-4(4')-hydroxylation of l-isoleucine in bacteria are also discussed. According to first hypothesis, the l-isoleucine dihydroxylation cascade is involved in synthesis of dipeptide antibiotic in P. ananatis. Another unifying hypothesis is that the C-4(4')-hydroxylation of l-isoleucine in bacteria could result in the synthesis of signal molecules belonging to two classes: 2(5H)-furanones and analogs of N-acyl homoserine lactone.

L-leucine 5-hydroxylase of Nostoc punctiforme is a novel type of Fe(II)/α-ketoglutarate-dependent dioxygenase that is useful as a biocatalyst.

L-Leucine 5-hydroxylase (LdoA) previously found in Nostoc punctiforme PCC 73102 is a novel type of Fe(II)/α-ketoglutarate-dependent dioxygenase. LdoA catalyzed regio- and stereoselective hydroxylation of L-leucine and L-norleucine into (2S,4S)-5-hydroxyleucine and (2S)-5-hydroxynorleucine, respectively. Moreover, LdoA catalyzed sulfoxidation of L-methionine and L-ethionine in the same manner as previously described L-isoleucine 4-hydroxylase. Therefore LdoA should be a promising biocatalyst for effective production of industrially useful amino acids.

A novel family of bacterial dioxygenases that catalyse the hydroxylation of free L-amino acids.

L-isoleucine-4-hydroxylase (IDO) is a recently discovered member of the Pfam family PF10014 (the former DUF 2257 family) of uncharacterized conserved bacterial proteins. To uncover the range of biochemical activities carried out by PF10014 members, eight in silico-selected IDO homologues belonging to the PF10014 were cloned and expressed in Escherichia coli. L-methionine, L-leucine, L-isoleucine and L-threonine were found to be catalysed by the investigated enzymes, producing L-methionine sulfoxide, 4-hydroxyleucine, 4-hydroxyisoleucine and 4-hydroxythreonine, respectively. An investigation of enzyme kinetics suggested the existence of a novel subfamily of bacterial dioxygenases within the PF10014 family for which free L-amino acids could be accepted as in vivo substrates. A hypothesis regarding the physiological significance of hydroxylated l-amino acids is also discussed.

Characterization of Bacillus thuringiensis L-isoleucine dioxygenase for production of useful amino acids.

We determined the enzymatic characteristics of an industrially important biocatalyst, α-ketoglutarate-dependent l-isoleucine dioxygenase (IDO), which was found to be the enzyme responsible for the generation of (2S,3R,4S)-4-hydroxyisoleucine in Bacillus thuringiensis 2e2. Depending on the amino acid used as the substrate, IDO catalyzed three different types of oxidation reactions: hydroxylation, dehydrogenation, and sulfoxidation. IDO stereoselectively hydroxylated several hydrophobic aliphatic l-amino acids, as well as l-isoleucine, and produced (S)-3-hydroxy-l-allo-isoleucine, 4-hydroxy-l-leucine, (S)-4-hydroxy-l-norvaline, 4-hydroxy-l-norleucine, and 5-hydroxy-l-norleucine. The IDO reaction product of l-isoleucine, (2S,3R,4S)-4-hydroxyisoleucine, was again reacted with IDO and dehydrogenated into (2S,3R)-2-amino-3-methyl-4-ketopentanoate, which is also a metabolite found in B. thuringiensis 2e2. Interestingly, IDO catalyzed the sulfoxidation of some sulfur-containing l-amino acids and generated l-methionine sulfoxide and l-ethionine sulfoxide. Consequently, the effective production of various modified amino acids would be possible using IDO as the biocatalyst.

Metabolic engineering of Escherichia coli to produce (2S, 3R, 4S)-4-hydroxyisoleucine.

The stereo-specific L-isoleucine-4-hydroxylase (L-isoleucine dioxygenase (IDO)) was cloned and expressed in an Escherichia coli 2Δ strain lacking the activities of α-ketoglutarate dehydrogenase (EC 1.2.4.2), isocitrate liase (EC 4.1.3.1), and isocitrate dehydrogenase kinase/phosphatase (EC 2.7.11.5). The 2Δ strain could not grow in a minimal-salt/glucose/glycerol medium due to the blockage of TCA during succinate synthesis. The IDO activity in the 2Δ strain was able to "shunt" destroyed TCA, thereby coupling L-isoleucine hydroxylation and cell growth. Using this strain, we performed the direct biotransformation of L-isoleucine into 4-HIL with an 82% yield.