Mechanism of Aromatic Amino Acid Hydroxylation

Fitzpatrick, Paul F.

doi:10.1021/bi035656u

Cited by 254 publications

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“…The crystal structures of the catalytic domains of all three enzymes show very similar folds and active sites (5-7), consistent with these enzymes sharing a common catalytic mechanism (8). The structures of the regulatory domains of PheH and TyrH show that both contain ACT domains (5,9,10), although the two enzymes are regulated differently (2,11).…”

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confidence: 54%

Identification of the Allosteric Site for Phenylalanine in Rat Phenylalanine Hydroxylase

Zhang

Fitzpatrick

2016

Journal of Biological Chemistry

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Liver phenylalanine hydroxylase (PheH) is an allosteric enzyme that requires activation by phenylalanine for full activity. The location of the allosteric site for phenylalanine has not been established. NMR spectroscopy of the isolated regulatory domain (RDPheH(25-117) is the regulatory domain of PheH lacking residues 1-24) of the rat enzyme in the presence of phenylalanine is consistent with formation of a side-by-side ACT dimer. Six residues in RDPheH(25-117) were identified as being in the phenylalanine-binding site on the basis of intermolecular NOEs between unlabeled phenylalanine and isotopically labeled protein. The location of these residues is consistent with two allosteric sites per dimer, with each site containing residues from both monomers. Site-specific variants of five of the residues (E44Q, A47G, L48V, L62V, and H64N) decreased the affinity of RDPheH(25-117) for phenylalanine based on the ability to stabilize the dimer. Incorporation of the A47G, L48V, and H64N mutations into the intact protein increased the concentration of phenylalanine required for activation. The results identify the location of the allosteric site as the interface of the regulatory domain dimer formed in activated PheH. Phenylalanine hydroxylase (PheH)2 catalyzes a key step in phenylalanine catabolism, the hydroxylation of phenylalanine to tyrosine in the liver using tetrahydropterin (BH 4 ) and oxygen. A deficiency in human PheH increases the level of phenylalanine in the blood, resulting in the inherited disease phenylketonuria (PKU) (1). Thus, the activity of PheH must be tightly controlled to maintain appropriate phenylalanine levels. PheH is activated by phenylalanine and inhibited by BH 4 (2, 3). In addition, phosphorylation of PheH at Ser-16 is reported to decrease the concentration of phenylalanine required to activate PheH (4).Mammalian PheH is a homotetramer, and each monomer contains an N-terminal regulatory domain, a central catalytic domain, and a C-terminal tetramerization domain. The other two aromatic amino acid hydroxylases, tyrosine hydroxylase (TyrH) and tryptophan hydroxylase, have similar architectures.The crystal structures of the catalytic domains of all three enzymes show very similar folds and active sites (5-7), consistent with these enzymes sharing a common catalytic mechanism (8). The structures of the regulatory domains of PheH and TyrH show that both contain ACT domains (5, 9, 10), although the two enzymes are regulated differently (2, 11). To date, there is no published structure of a full-length mammalian PheH, or indeed of any eukaryotic aromatic amino acid hydroxylase, in that the available structures are of proteins lacking the N-terminal regulatory domain, much of the C-terminal tetramerization domain, or both. The structure of a dimeric form of rat PheH containing both the catalytic and regulatory domains but lacking the C-terminal 24 residues required for tetramer formation (5) has provided the present model for the structural basis for activation by phenylalanine. In this structure the...

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confidence: 54%

Identification of the Allosteric Site for Phenylalanine in Rat Phenylalanine Hydroxylase

Zhang

Fitzpatrick

2016

Journal of Biological Chemistry

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“…For all three enzymes, hydroxylation of the physiological substrate occurs via an electrophilic aromatic substitution reaction with an activated oxygen species [13][14][15]. In the case of TyrH the latter has been shown to be an Fe(IV) species [16], consistent with the proposed involvement of an Fe(IV)O as the hydroxylating intermediate in all three enzymes [12]. The reactivities of the hydroxylating intermediates in all three enzymes are similar [17] and they have overlapping substrate specificities [18][19][20], supporting the proposal for a common Fe(IV)O intermediate.…”

supporting

confidence: 64%

“…The similar structures of the catalytic domains [9][10][11] and a variety of mechanistic studies suggest that the three aromatic amino acid hydroxylases share a common catalytic mechanism [12]. For all three enzymes, hydroxylation of the physiological substrate occurs via an electrophilic aromatic substitution reaction with an activated oxygen species [13][14][15].…”

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confidence: 98%

Characterization of metal ligand mutants of phenylalanine hydroxylase: Insights into the plasticity of a 2-histidine-1-carboxylate triad

Fitzpatrick

2008

Archives of Biochemistry and Biophysics

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The iron atom in the nonheme iron monooxygenase phenylalanine hydroxylase is bound on one face by His285, His290, and Glu330. This arrangement of metal ligands is conserved in the other aromatic amino acid hydroxylases, tyrosine hydroxylase and tryptophan hydroxylase. A similar 2-His-1-carboxylate facial triad of two histidines and an acidic residue are the ligands to the iron in other nonheme iron enzymes, including the α-ketoglutarate dependent hydroxylases and the extradiol dioxygenases. Previous studies of the effects of conservative mutations of the iron ligands in tyrosine hydroxylase established that there is some plasticity in the nature of the ligands and that the three ligands differ in their sensitivity to mutagenesis. To determine the generality of this finding for enzymes containing a 2-His-1-carboxylate facial triad, the His285, His290, and Glu330 in rat phenylalanine hydroxylase were mutated to glutamine, glutamate, and histidine. All of the mutant proteins had low but measurable activities for tyrosine formation. In general, mutation of Glu330 had the greatest effect on activity and mutation of His290 the least. All of the mutations resulted in an excess of tetrahydropterin oxidized relative to tyrosine formation, with mutation of His285 having the greatest effect on the coupling of the two partial reactions. The H285Q enzyme had the highest activity as tetrahydropterin oxidase at 20% the wild-type value. All of the mutations greatly decreased the affinity for iron, with mutation of Glu330 the most deleterious. The results complement previous results with tyrosine hydroxylase in establishing the plasticity of the individual iron ligands in this enzyme family.Phenylalanine hydroxylase (PheH) 1 is a tetrahydropterin-dependent nonheme enzyme that catalyzes the hydroxylation of phenylalanine to tyrosine, an important pathway for phenylalanine catabolism (Scheme 1) [1]. As a liver enzyme, PheH is critical for catabolizing excess phenylalanine in the diet. Consequently, a deficiency in PheH results in the debilitating disease phenylketonuria [2]. PheH belongs to the small family of aromatic amino acid hydroxylases, all of which use tetrahydrobiopterin as the source of electrons to hydroxylate the aromatic ring of an aromatic amino acid. Tyrosine hydroxylase (TyrH) and tryptophan †

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“…6) (28). Tryptophan hydroxylase belongs to a family of aromatic amino acid hydroxylases and requires iron and the coenzyme tetrahydropterin for catalytic activity (29). It is interesting that the SL gene encodes CYP71P1 in the P450 superfamily, which is different from the tetrahydropterin-dependent hydroxylase family in mammals (Fig.…”

Section: Discussionmentioning

confidence: 99%

Sekiguchi Lesion Gene Encodes a Cytochrome P450 Monooxygenase That Catalyzes Conversion of Tryptamine to Serotonin in Rice

Fujiwara

Maisonneuve

Isshiki

et al. 2010

Journal of Biological Chemistry

198

192

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Serotonin is a well known neurotransmitter in mammals and plays an important role in various mental functions in humans. In plants, the serotonin biosynthesis pathway and its function are not well understood. The rice sekiguchi lesion (sl) mutants accumulate tryptamine, a candidate substrate for serotonin biosynthesis. We isolated the SL gene by map-based cloning and found that it encodes CYP71P1 in a cytochrome P450 monooxygenase family. A recombinant SL protein exhibited tryptamine 5-hydroxylase enzyme activity and catalyzed the conversion of tryptamine to serotonin. This pathway is novel and has not been reported in mammals. Expression of SL was induced by the N-acetylchitooligosaccharide (chitin) elicitor and by infection with Magnaporthe grisea, a causal agent for rice blast disease. Exogenously applied serotonin induced defense gene expression and cell death in rice suspension cultures and increased resistance to rice blast infection in plants. We also found that serotonin-induced defense gene expression is mediated by the RacGTPase pathway and by the G␣ subunit of the heterotrimeric G protein. These results suggest that serotonin plays an important role in rice innate immunity.

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Mechanism of Aromatic Amino Acid Hydroxylation

Cited by 254 publications

References 91 publications

Identification of the Allosteric Site for Phenylalanine in Rat Phenylalanine Hydroxylase

Identification of the Allosteric Site for Phenylalanine in Rat Phenylalanine Hydroxylase

Characterization of metal ligand mutants of phenylalanine hydroxylase: Insights into the plasticity of a 2-histidine-1-carboxylate triad

Sekiguchi Lesion Gene Encodes a Cytochrome P450 Monooxygenase That Catalyzes Conversion of Tryptamine to Serotonin in Rice

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