MIO (3,5-dihydro-5-methylidene-4H-imidazol-4-one)-dependent aminomutases begin their reactions by adding the amino group of the substrate to the methylidene carbon of the MIO prosthesis. The enzyme removes the NH2/H pair from the substrate, yielding an NH2-MIO adduct, a tightly bound acrylate intermediate, and protonated catalytic Tyr
the 3,5-dihydro-5-methylidene-4H-imidazol-4-one (MIO) group in the enzyme's active site N-alkylates the NH2 of the alpha-amino acid substrates and promotes the removal of an intermediary NH2-MIO adduct. Concomitant removal of a beta-proton from the substrate (NH2-MIO adduct) by a catalytic tyrosine yields an acrylate intermediate. The aminomutase reaction continues by vicinal reprotonation and reamination at the alpha- and beta-carbons, respectively, of the acrylate to produce the beta-amino acid. Mechanism of MIO-dependent aminomutase, overview
the enzyme isomerizes (S)-alpha-tyrosine to (R)-beta-tyrosine and is stereoselective for (R)-beta-tyrosine (85%), but also forms the (S)-beta-tyrosine enantiomer (15%) through inversion of configuration at both migration termini
the 3,5-dihydro-5-methylidene-4H-imidazol-4-one (MIO) group in the enzyme's active site N-alkylates the NH2 of the alpha-amino acid substrates and promotes the removal of an intermediary NH2-MIO adduct. Concomitant removal of a beta-proton from the substrate (NH2-MIO adduct) by a catalytic tyrosine yields an acrylate intermediate. The aminomutase reaction continues by vicinal reprotonation and reamination at the alpha- and beta-carbons, respectively, of the acrylate to produce the beta-amino acid. Autocatalysis of the 3,5-dihydro-5-methylidene-4H-imidazol-4-one (MIO) cofactor through cyclization of (A/T/S)-Ser-Gly residues within the active site
i.e. MIO, dependent on. The MIO group is formed by condensation and cyclization of backbone residues of an (A, T, or S)-Ser-Gly triad in the active site. The MIO N-alkylates the NH2 of the alpha-amino acid substrates and promotes the removal of an intermediary NH2-MIO adduct. Concomitant removal of a beta-proton from the substrate (NH2-MIO adduct) by a catalytic tyrosine yields an acrylate intermediate
i.e. MIO, dependent on. The MIO group is formed by condensation and cyclization of backbone residues of an (A, T, or S)-Ser-Gly triad in the active site. The MIO N-alkylates the NH2 of the alpha-amino acid substrates and promotes the removal of an intermediary NH2-MIO adduct. Concomitant removal of a beta-proton from the substrate (NH2-MIO adduct) by a catalytic tyrosine yields an acrylate intermediate. Autocatalysis of the 3,5-dihydro-5-methylidene-4H-imidazol-4-one (MIO) cofactor through cyclization of (A/T/S)-Ser-Gly residues within the active site, overview
(R)-beta-tyrosine occurs in the seeds, leaves, roots, and root exudates of the Nipponbare cultivar. Dry rice seeds from plants that have not been elicited with jasmonic acid also contain significant amounts of beta-tyrosine. When rice seedlings are grown hydroponically, beta-tyrosine is secreted into the medium
MIO-dependent aminomutases belong to a class I lyase-like family, in which the MIO group is formed by condensation and cyclization of backbone residues of an (A, T, or S)-Ser-Gly triad in the active site. The active sites of rice tyrosine aminomutase and Taxus canadensis phenylalanine aminomutase share a high degree of sequence identity, which may in part explain why OsTAM also converts phenylalanine to beta-phenylalanine
MIO (3,5-dihydro-5-methylidene-4H-imidazol-4-one)-dependent aminomutases (AMs) are involved in the the biosynthetic pathways of biologically active, medicinal compounds in plants and microorganisms
tyrosine aminomutase TAM1 is required for beta-tyrosine biosynthesis in Oryza sativa, the tyrosine aminomutase converts the common protein amino acid tyrosine (alpha-tyrosine) into beta-tyrosine. beta-Tyrosine is most prevalent in temperate japonica cultivars. beta-Tyrosine is exuded into hydroponic medium at higher concentrations and may contribute to the allelopathic potential of rice. Pseudomonas syringae growth is inhibited by beta-tyrosine, and seedlings of dicot species are much more sensitive to exogenous beta-tyrosine than rice and other tested monocots
homology modeling of wild-type enzyme OsTAM and OsTAM mutant enzymes using the phenylalanine aminomutase structure from Taxus canadensis with PDB ID 3NZ4 as template. The active site of enzyme TAM has a flexible inner loop region
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CRYSTALLIZATION (Commentary)
ORGANISM
UNIPROT
LITERATURE
mutant enzyme E71A using 100 mM trimethylamine N-oxide, 4.6 M sodium formate, at 4°C, and mutant enzyme Y63F using 95 mM trimethylamine N-oxide, 4.6 M sodium formate with 2 mM L-tyrosine, at 20°C
site-directed mutagenesis, the mutant shows increased activity with phenylalanine and halogenated phenylalanine substrates compared to the wild-type enzyme
site-directed mutagenesis, the mutant shows increased activity with phenylalanine and halogenated phenylalanine substrates compared to the wild-type enzyme, the mutant activity is reduced at converting alpha-tyrosine to its beta-isomer and 4-coumarate (ratio 22:78) compared to the wild-type, the mutant binds alpha-phenylalanine about 9fold better than wild-type OsTAM, total turnover rate of the mutant for converting alpha-phenylalanine to both beta-phenylalanine and cinnamate is about 4fold greater than the wild-type OsTAM rate for making beta-phenylalanine and cinnamate. Mutation of Asn446 of OsTAM to a Lys residue creates an active site bearing the characteristic triad sequence ([aromatic amino acid]-Leu-Lys) conserved in all PALs and thus explains in part why N446K-OsTAM has increased PAL activity compared to wild-type OsTAM
site-directed mutagenesis, the mutant shows altered activity with phenylalanine and halogenated phenylalanine substrates compared to the wild-type enzyme
site-directed mutagenesis, the mutant shows altered activity with phenylalanine and halogenated phenylalanine substrates compared to the wild-type enzyme, mutant activity is reduced at converting alpha-tyrosine to its beta-isomer and 4-coumarate (ratio 2:98) compared to the wild-type, the mutant binds alpha-phenylalanine about 9fold better than wild-type OsTAM, total turnover rate of the mutant for converting alpha-phenylalanine to both beta-phenylalanine and cinnamate is about 4fold greater than the wild-type OsTAM rate for making beta-phenylalanine and cinnamate
site-directed mutagenesis, inactive mutant with L-tyrosine, the mutant binds alpha-phenylalanine about 9fold better than wild-type OsTAM, the mutant converts alpha-phenylalanine to both beta-phenylalanine and cinnamate
site-directed mutagenesis, the mutant shows altered activity with phenylalanine and halogenated phenylalanine substrates compared to the wild-type enzyme
homology modeling of wild-type enzyme OsTAM and OsTAM mutant enzymes using the phenylalanine aminomutase (PAM) structure from Taxus canadensis with PDB ID 3NZ4 as template. Exchanging the active residues of OsTAM, Y125C and N446K for those in a phenylalanine aminomutase Taxus canadensis PAM alters its substrate specificity from tyrosine to phenylalanine
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EXPRESSION
ORGANISM
UNIPROT
LITERATURE
beta-tyrosine accumulation is induced by the plant defense signaling molecule jasmonic acid, jasmonic acid treatment of the seedlings increases beta-tyrosine content in the leaves, roots, and imbibed seed material.