Pyridoxal Enzymes: Mechanistic Diversity and Uniformity

Hayashi, Hideyuki

doi:10.1093/oxfordjournals.jbchem.a124931

Cited by 167 publications

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“…Assays were performed for 1 h at 30°C in HEPES buffer at the pH values indicated in the presence of 2 mg of purified enzyme, 3 mM L-Tyr, 0.1 mM PLP, 0.1 mM EDTA, and 0.5 mM a-ketoglutarate. e-amino group of the Lys residue via a Schiff base linkage (Hayashi, 1995). Once the amino acid substrate interacts with the active site, a new Schiff base is generated.…”

Section: Involvement Of Tyrat In Bia Metabolism In Opium Poppymentioning

confidence: 99%

“…This reaction is readily reversible; thus, both amino acids and a-keto acids are substrates for transaminases. Pyridoxal-5#-phosphate (PLP) functions as a coenzyme forming a Schiff base with the amino acid, which is required for activity and involves a conserved Lys residue at the catalytic core of all aminotransferases (Hayashi, 1995). PLP-dependent aminotransferases are divided into four subgroups based on sequence identity.…”

mentioning

confidence: 99%

“…Subgroup II includes acetyl-Orn aminotransferase, Orn aminotransferase, and Lys aminotransferase. Subgroups III and IV include Ser aminotransferase, phospho-Ser aminotransferase, D-amino acid aminotransferases, and branched-chain amino acid aminotransferases (Hayashi, 1995).…”

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confidence: 99%

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Tyrosine Aminotransferase Contributes to Benzylisoquinoline Alkaloid Biosynthesis in Opium Poppy

Lee

Facchini

2011

Plant Physiology

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Tyrosine aminotransferase (TyrAT) catalyzes the transamination of L-Tyr and a-ketoglutarate, yielding 4-hydroxyphenylpyruvic acid and L-glutamate. The decarboxylation product of 4-hydroxyphenylpyruvic acid, 4-hydroxyphenylacetaldehyde, is a precursor to a large and diverse group of natural products known collectively as benzylisoquinoline alkaloids (BIAs). We have isolated and characterized a TyrAT cDNA from opium poppy (Papaver somniferum), which remains the only commercial source for several pharmaceutical BIAs, including codeine, morphine, and noscapine. TyrAT belongs to group I pyridoxal 5#-phosphate (PLP)-dependent enzymes wherein Schiff base formation occurs between PLP and a specific Lys residue. The amino acid sequence of TyrAT showed considerable homology to other putative plant TyrATs, although few of these have been functionally characterized. Purified, recombinant TyrAT displayed a molecular mass of approximately 46 kD and a substrate preference for L-Tyr and a-ketoglutarate, with apparent K m values of 1.82 and 0.35 mM, respectively. No specific requirement for PLP was detected in vitro. Liquid chromatography-tandem mass spectrometry confirmed the conversion of L-Tyr to 4-hydroxyphenylpyruvate. TyrAT gene transcripts were most abundant in roots and stems of mature opium poppy plants. Virus-induced gene silencing was used to evaluate the contribution of TyrAT to BIA metabolism in opium poppy. TyrAT transcript levels were reduced by at least 80% in silenced plants compared with controls and showed a moderate reduction in total alkaloid content. The modest correlation between transcript levels and BIA accumulation in opium poppy supports a role for TyrAT in the generation of alkaloid precursors, but it also suggests the occurrence of other sources for 4-hydroxyphenylacetaldehyde.

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Section: Involvement Of Tyrat In Bia Metabolism In Opium Poppymentioning

confidence: 99%

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confidence: 99%

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Tyrosine Aminotransferase Contributes to Benzylisoquinoline Alkaloid Biosynthesis in Opium Poppy

Lee

Facchini

2011

Plant Physiology

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“…The absence of the transamination activity in chDSD can also be explained on the basis of the present crystal structure. In the case of aminotransferases, an acidic residue forms a hydrogen bond with the N1 atom, resulting in the protonation of the N1 atom (42). Importantly, the quinonoid intermediate, which is necessary for conversion to the ketimine intermediate in the transamination reaction (42), is stabilized through the protonated N1 atom.…”

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confidence: 99%

“…In the case of aminotransferases, an acidic residue forms a hydrogen bond with the N1 atom, resulting in the protonation of the N1 atom (42). Importantly, the quinonoid intermediate, which is necessary for conversion to the ketimine intermediate in the transamination reaction (42), is stabilized through the protonated N1 atom. On the other hand, because the N1 atom of PLP forms a hydrogen bond with the hydroxyl group of Tyr 174 in chDSD (Fig.…”

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confidence: 99%

Crystal Structure of a Zinc-dependent d-Serine Dehydratase from Chicken Kidney

Tanaka

Senda

Venugopalan

et al. 2011

Journal of Biological Chemistry

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D-Serine is a co-agonist of the NMDA receptor, an excitatory neurotransmitter receptor important for higher brain functions, including learning and memory (1, 2). The NMDA receptor is a glutamate-gated ion channel (3), and glutamate does not activate the receptor unless a co-agonist binding site is simultaneously occupied by D-serine or glycine (4). Because significant concentrations of D-serine exist in vertebrate brains (5), D-serine is believed to physiologically control the sensitivity of the NMDA receptor to glutamate (6).In mammals, D-serine is produced by a bifunctional serine racemase/dehydratase (7) and is mainly degraded by D-amino acid oxidase (2, 7). In rat brains, the localization of D-amino acid oxidase activity is reciprocal to that of D-serine (8, 9), suggesting that D-amino acid oxidase determines the basal levels of D-serine in mammalian brains. However, we have found recently that, in the chicken brain, D-serine is degraded mainly by a D-serine dehydratase (DSD) 4 (10), which catalyzes the ␣,␤-elimination of water from D-serine to form pyruvate and ammonia. In addition, we have found that the chicken DSD (chDSD) has a primary structure similar to those of metal-activated D-threonine aldolases (11-13), which are fold-type III PLP-dependent enzymes (14), and is distinct from a well known metal-independent bacterial DSD (dsdA) belonging to the foldtype II PLP-dependent enzyme family (14,15). Interestingly, a fold-type III family protein coded by gene YGL196W of Saccharomyces cerevisiae was recently identified as a zinc-dependent DSD (scDSD) (16). To understand why avian species use DSD to metabolize D-serine in the brain and its physiological functions, it is important to reveal the structural and enzymatic properties of this novel DSD family.In the present study, we showed that chDSD requires Zn 2ϩ just as scDSD does. Then, to reveal the catalytic roles of Zn 2ϩ in the dehydration of D-serine, we determined the crystal structures of chDSD, EDTA-treated chDSD, and the EDTA-treated chDSD⅐D-serine complex. Although there is only one DSD entry in the Protein Data Bank (PDB), DSD from Burkholderia xenovorans LB400 (PDB code 3GWQ), the structure contains neither PLP nor zinc, and the enzymatic properties of this DSD *

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Structure modelling and site-directed mutagenesis of the rat aromatic L-amino acid pyridoxal 5´-phosphate-dependent decarboxylase: A functional study

et al. 1999

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The pyridoxal-5Ј-phosphate-dependent enzymes (B 6 enzymes) are grouped into three main families named ␣, ␤, and ␥. Proteins in the ␣ and ␥ families share the same fold and might be distantly related, while those in the ␤ family exhibit specific structural features. The rat aromatic L-amino acid decarboxylase (AADC; EC(4.1.1.28)) catalyzes the synthesis of two important neurotransmitters: dopamine and serotonin. It binds the cofactor pyridoxal-5Ј-phosphate and belongs to the ␣ family. Despite the low level of sequence identity (approximately 10%) shared by the rat AADC and the sequences of the enzymes belonging to the B 6 enzymes family, including the known three-dimensional structures, a multiple sequence alignment was deduced. A model was built using segments belonging to seven of the eleven known structures. By homology, and based on knowledge of the biochemistry of the aspartate aminotransferase, structurally and functionally important residues were identified in the rat AADC. Site-directed mutagenesis of the conserved residues D271, T246, and C311 was carried out in order to confirm our predictions and highlight their functional role. Mutation of D271A and D271N resulted in complete loss of enzyme activity, while the D271E mutant exhibited 2% of the wild-type activity. Substitution of T246A resulted in 5% of the wild-type activity while the C311A mutant conserved 42% of the wild-type activity. A functional model of the AADC is discussed in view of the structural model and the complementary mutagenesis and labelling studies. Proteins 1999;37:191-203.

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Pyridoxal Enzymes: Mechanistic Diversity and Uniformity

Cited by 167 publications

References 0 publications

Tyrosine Aminotransferase Contributes to Benzylisoquinoline Alkaloid Biosynthesis in Opium Poppy

Tyrosine Aminotransferase Contributes to Benzylisoquinoline Alkaloid Biosynthesis in Opium Poppy

Crystal Structure of a Zinc-dependent d-Serine Dehydratase from Chicken Kidney

Structure modelling and site-directed mutagenesis of the rat aromatic L-amino acid pyridoxal 5´-phosphate-dependent decarboxylase: A functional study

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