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Leandro J, Stokka AJ, Teigen K, Andersen OA, Flatmark T. Substituting Tyr 138 in the active site loop of human phenylalanine hydroxylase affects catalysis and substrate activation. FEBS Open Bio 2017; 7:1026-1036. [PMID: 28680815 PMCID: PMC5494296 DOI: 10.1002/2211-5463.12243] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2017] [Revised: 04/27/2017] [Accepted: 05/10/2017] [Indexed: 11/22/2022] Open
Abstract
Mammalian phenylalanine hydroxylase (PAH) is a key enzyme in l‐phenylalanine (l‐Phe) metabolism and is active as a homotetramer. Biochemical and biophysical work has demonstrated that it cycles between two states with a variably low and a high activity, and that the substrate l‐Phe is the key player in this transition. X‐ray structures of the catalytic domain have shown mobility of a partially intrinsically disordered Tyr138‐loop to the active site in the presence of l‐Phe. The mechanism by which the loop dynamics are coupled to substrate binding at the active site in tetrameric PAH is not fully understood. We have here conducted functional studies of four Tyr138 point mutants. A high linear correlation (r2 = 0.99) was observed between their effects on the catalytic efficiency of the catalytic domain dimers and the corresponding effect on the catalytic efficiency of substrate‐activated full‐length tetramers. In the tetramers, a correlation (r2 = 0.96) was also observed between the increase in catalytic efficiency (activation) and the global conformational change (surface plasmon resonance signal response) at the same l‐Phe concentration. The new data support a similar functional importance of the Tyr138‐loop in the catalytic domain and the full‐length enzyme homotetramer.
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Affiliation(s)
- João Leandro
- Department of Biomedicine University of Bergen Norway.,Metabolism and Genetics Group Research Institute for Medicines (iMed.ULisboa) Faculty of Pharmacy University of Lisbon Portugal.,Present address: Department of Genetics and Genomic Sciences Icahn School of Medicine at Mount Sinai 1425 Madison Avenue, Box 1498 New York NY 10029 USA
| | - Anne J Stokka
- Department of Biomedicine University of Bergen Norway.,The Biotechnology Centre of Oslo University of Oslo Norway
| | - Knut Teigen
- Department of Biomedicine University of Bergen Norway
| | - Ole A Andersen
- Department of Biomedicine University of Bergen Norway.,Evotec (UK) Ltd .Abingdon UK
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2
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Leandro J, Saraste J, Leandro P, Flatmark T. PKU mutation p.G46S prevents the stereospecific binding of l-phenylalanine to the dimer of human phenylalanine hydroxylase regulatory domain. FEBS Open Bio 2017; 7:195-203. [PMID: 28174686 PMCID: PMC5292662 DOI: 10.1002/2211-5463.12175] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2016] [Revised: 12/01/2016] [Accepted: 12/03/2016] [Indexed: 11/23/2022] Open
Abstract
Mammalian phenylalanine hydroxylase (PAH) has a potential allosteric regulatory binding site for l‐phenylalanine (l‐Phe), in addition to its catalytic site. This arrangement is supported by a crystal structure of a homodimeric truncated form of the regulatory domain of human PAH (hPAH‐RD1–118/19–118) [Patel D et al. (2016) Sci Rep doi: 10.1038/srep23748]. In this study, a fusion protein of the domain (MBP‐(pepXa)‐hPAH‐RD1–120) was overexpressed and recovered in a metastable and soluble state, which allowed the isolation of a dimeric and a monomeric fusion protein. When cleaved from MBP, hPAH‐RD forms aggregates which are stereospecifically inhibited by l‐Phe (> 95%) at low physiological concentrations. Aggregation of the cleaved dimer of the mutant form hPAH‐G46S‐RD was not inhibited by l‐Phe, which is compatible with structurally/conformationally changed βαββαβ ACT domain folds in the mutant.
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Affiliation(s)
- João Leandro
- Department of Biomedicine University of Bergen Norway; Metabolism and Genetics Group Research Institute for Medicines and Pharmaceutical Sciences (iMed.UL) Faculty of Pharmacy University of Lisbon Portugal
| | | | - Paula Leandro
- Metabolism and Genetics Group Research Institute for Medicines and Pharmaceutical Sciences (iMed.UL) Faculty of Pharmacy University of Lisbon Portugal
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3
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Zhang S, Fitzpatrick PF. Identification of the Allosteric Site for Phenylalanine in Rat Phenylalanine Hydroxylase. J Biol Chem 2016; 291:7418-25. [PMID: 26823465 DOI: 10.1074/jbc.m115.709998] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2015] [Indexed: 11/06/2022] Open
Abstract
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.
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Affiliation(s)
- Shengnan Zhang
- From the Department of Biochemistry, University of Texas Health Science Center, San Antonio, Texas 78229
| | - Paul F Fitzpatrick
- From the Department of Biochemistry, University of Texas Health Science Center, San Antonio, Texas 78229
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4
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Zhang S, Hinck AP, Fitzpatrick PF. The Amino Acid Specificity for Activation of Phenylalanine Hydroxylase Matches the Specificity for Stabilization of Regulatory Domain Dimers. Biochemistry 2015; 54:5167-74. [PMID: 26252467 PMCID: PMC4551101 DOI: 10.1021/acs.biochem.5b00616] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
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Liver
phenylalanine hydroxylase is allosterically activated by
phenylalanine. The structural changes that accompany activation have
not been identified, but recent studies of the effects of phenylalanine
on the isolated regulatory domain of the enzyme support a model in
which phenylalanine binding promotes regulatory domain dimerization.
Such a model predicts that compounds that stabilize the regulatory
domain dimer will also activate the enzyme. Nuclear magnetic resonance
spectroscopy and analytical ultracentrifugation were used to determine
the ability of different amino acids and phenylalanine analogues to
stabilize the regulatory domain dimer. The abilities of these compounds
to activate the enzyme were analyzed by measuring their effects on
the fluorescence change that accompanies activation and on the activity
directly. At concentrations of 10–50 mM, d-phenylalanine, l-methionine, l-norleucine, and (S)-2-amino-3-phenyl-1-propanol were able to activate the enzyme to
the same extent as 1 mM l-phenylalanine. Lower levels of
activation were seen with l-4-aminophenylalanine, l-leucine, l-isoleucine, and 3-phenylpropionate. The ability
of these compounds to stabilize the regulatory domain dimer agreed
with their ability to activate the enzyme. These results support a
model in which allosteric activation of phenylalanine hydroxylase
is linked to dimerization of regulatory domains.
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Affiliation(s)
- Shengnan Zhang
- Department of Biochemistry, University of Texas Health Science Center , San Antonio, Texas 78229, United States
| | - Andrew P Hinck
- Department of Biochemistry, University of Texas Health Science Center , San Antonio, Texas 78229, United States
| | - Paul F Fitzpatrick
- Department of Biochemistry, University of Texas Health Science Center , San Antonio, Texas 78229, United States
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5
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Roberts KM, Khan CA, Hinck CS, Fitzpatrick PF. Activation of phenylalanine hydroxylase by phenylalanine does not require binding in the active site. Biochemistry 2014; 53:7846-53. [PMID: 25453233 PMCID: PMC4270383 DOI: 10.1021/bi501183x] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
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Phenylalanine
hydroxylase (PheH), a liver enzyme that catalyzes
the hydroxylation of excess phenylalanine in the diet to tyrosine,
is activated by phenylalanine. The lack of activity at low levels
of phenylalanine has been attributed to the N-terminus of the protein’s
regulatory domain acting as an inhibitory peptide by blocking substrate
access to the active site. The location of the site at which phenylalanine
binds to activate the enzyme is unknown, and both the active site
in the catalytic domain and a separate site in the N-terminal regulatory
domain have been proposed. Binding of catecholamines to the active-site
iron was used to probe the accessibility of the active site. Removal
of the regulatory domain increases the rate constants for association
of several catecholamines with the wild-type enzyme by ∼2-fold.
Binding of phenylalanine in the active site is effectively abolished
by mutating the active-site residue Arg270 to lysine. The kcat/Kphe value is
down 104 for the mutant enzyme, and the Km value for phenylalanine for the mutant enzyme is >0.5
M. Incubation of the R270K enzyme with phenylalanine also results
in a 2-fold increase in the rate constants for catecholamine binding.
The change in the tryptophan fluorescence emission spectrum seen in
the wild-type enzyme upon activation by phenylalanine is also seen
with the R270K mutant enzyme in the presence of phenylalanine. Both
results establish that activation of PheH by phenylalanine does not
require binding of the amino acid in the active site. This is consistent
with a separate allosteric site, likely in the regulatory domain.
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Affiliation(s)
- Kenneth M Roberts
- Department of Biochemistry, University of Texas Health Science Center , San Antonio, Texas 78229, United States
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6
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Ronau JA, Paul LN, Fuchs JE, Corn IR, Wagner KT, Liedl KR, Abu-Omar MM, Das C. An additional substrate binding site in a bacterial phenylalanine hydroxylase. EUROPEAN BIOPHYSICS JOURNAL : EBJ 2013; 42:691-708. [PMID: 23860686 PMCID: PMC3972754 DOI: 10.1007/s00249-013-0919-8] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/20/2013] [Revised: 06/20/2013] [Accepted: 06/26/2013] [Indexed: 01/07/2023]
Abstract
Phenylalanine hydroxylase (PAH) is a non-heme iron enzyme that catalyzes oxidation of phenylalanine to tyrosine, a reaction that must be kept under tight regulatory control. Mammalian PAH has a regulatory domain in which binding of the substrate leads to allosteric activation of the enzyme. However, the existence of PAH regulation in evolutionarily distant organisms, for example some bacteria in which it occurs, has so far been underappreciated. In an attempt to crystallographically characterize substrate binding by PAH from Chromobacterium violaceum, a single-domain monomeric enzyme, electron density for phenylalanine was observed at a distal site 15.7 Å from the active site. Isothermal titration calorimetry (ITC) experiments revealed a dissociation constant of 24 ± 1.1 μM for phenylalanine. Under the same conditions, ITC revealed no detectable binding for alanine, tyrosine, or isoleucine, indicating the distal site may be selective for phenylalanine. Point mutations of amino acid residues in the distal site that contact phenylalanine (F258A, Y155A, T254A) led to impaired binding, consistent with the presence of distal site binding in solution. Although kinetic analysis revealed that the distal site mutants suffer discernible loss of their catalytic activity, X-ray crystallographic analysis of Y155A and F258A, the two mutants with the most noticeable decrease in activity, revealed no discernible change in the structure of their active sites, suggesting that the effect of distal binding may result from protein dynamics in solution.
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Affiliation(s)
- Judith A. Ronau
- Brown Laboratory of Chemistry, Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, IN-47907, USA
| | - Lake N. Paul
- Bindley Biosciences Center, Purdue University, West Lafayette, IN 47907, USA
| | - Julian E. Fuchs
- Institute of General, Inorganic and Theoretical Chemistry, and Center for Molecular Biosciences Innsbruck (CMBI), University of Innsbruck, Innrain 80/82, A-6020 Innsbruck, Austria
| | - Isaac R. Corn
- Brown Laboratory of Chemistry, Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, IN-47907, USA
| | - Kyle T. Wagner
- Brown Laboratory of Chemistry, Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, IN-47907, USA
| | - Klaus R. Liedl
- Institute of General, Inorganic and Theoretical Chemistry, and Center for Molecular Biosciences Innsbruck (CMBI), University of Innsbruck, Innrain 80/82, A-6020 Innsbruck, Austria
| | - Mahdi M. Abu-Omar
- Brown Laboratory of Chemistry, Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, IN-47907, USA
| | - Chittaranjan Das
- Brown Laboratory of Chemistry, Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, IN-47907, USA,To whom correspondence should be addressed: Chittaranjan Das, Brown Laboratory of Chemistry, 560 Oval Drive, West Lafayette, IN, 47907, (765)-494-5478, Fax: (765)-494-0239,
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7
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Chen P, Li L, Wang J, Li H, Li Y, Lv Y, Lu C. BmPAH catalyzes the initial melanin biosynthetic step in Bombyx mori. PLoS One 2013; 8:e71984. [PMID: 23991017 PMCID: PMC3753331 DOI: 10.1371/journal.pone.0071984] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2013] [Accepted: 07/06/2013] [Indexed: 11/19/2022] Open
Abstract
Pigmentation during insect development is a primal adaptive requirement. In the silkworm, melanin is the primary component of larval pigments. The rate limiting substrate in melanin synthesis is tyrosine, which is converted from phenylalanine by the rate-limiting enzyme phenylalanine hydroxylase (PAH). While the role of tyrosine, derived from phenylalanine, in the synthesis of fiber proteins has long been known, the role of PAH in melanin synthesis is still unknown in silkworm. To define the importance of PAH, we cloned the cDNA sequence of BmPAH and expressed its complete coding sequence using the Bac-to-Bac baculovirus expression system. Purified recombinant protein had high PAH activity, some tryptophan hydroxylase activity, but no tyrosine hydroxylase activity, which are typical properties of PAH in invertebrates. Because melanin synthesis is most robust during the embryonic stage and larval integument recoloring stage, we injected BmPAH dsRNA into silkworm eggs and observed that decreasing BmPAH mRNA reduced neonatal larval tyrosine and caused insect coloration to fail. In vitro cultures and injection of 4th instar larval integuments with PAH inhibitor revealed that PAH activity was essential for larval marking coloration. These data show that BmPAH is necessary for melanin synthesis and we propose that conversion of phenylalanine to tyrosine by PAH is the first step in the melanin biosynthetic pathway in the silkworm.
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Affiliation(s)
- Ping Chen
- State Key Laboratory of Silkworm Genome Biology and College of Biotechnology, Southwest University, Chongqing, China ; College of Biotechnology, Southwest University, Chongqing, China
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8
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Flydal MI, Martinez A. Phenylalanine hydroxylase: function, structure, and regulation. IUBMB Life 2013; 65:341-9. [PMID: 23457044 DOI: 10.1002/iub.1150] [Citation(s) in RCA: 125] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2012] [Accepted: 01/09/2013] [Indexed: 11/08/2022]
Abstract
Mammalian phenylalanine hydroxylase (PAH) catalyzes the rate-limiting step in the phenylalanine catabolism, consuming about 75% of the phenylalanine input from the diet and protein catabolism under physiological conditions. In humans, mutations in the PAH gene lead to phenylketonuria (PKU), and most mutations are mainly associated with PAH misfolding and instability. The established treatment for PKU is a phenylalanine-restricted diet and, recently, supplementation with preparations of the natural tetrahydrobiopterin cofactor also shows effectiveness for some patients. Since 1997 there has been a significant increase in the understanding of the structure, catalytic mechanism, and regulation of PAH by its substrate and cofactor, in addition to improved correlations between genotype and phenotype in PKU. Importantly, there has also been an increased number of studies on the structure and function of PAH from bacteria and lower eukaryote organisms, revealing an additional anabolic role of the enzyme in the synthesis of melanin-like pigments. In this review, we discuss these recent studies, which contribute to define the evolutionary adaptation of the PAH structure and function leading to sophisticated regulation for effective catabolic processing of phenylalanine in mammalian organisms.
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Affiliation(s)
- Marte I Flydal
- Department of Biomedicine and K.G. Jebsen Centre for Research on Neuropsychiatric Disorders, University of Bergen, Jonas Lies vei 91, 5009-Bergen, Norway
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9
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Flydal MI, Chatfield CH, Zheng H, Gunderson FF, Aubi O, Cianciotto NP, Martinez A. Phenylalanine hydroxylase from Legionella pneumophila is a thermostable enzyme with a major functional role in pyomelanin synthesis. PLoS One 2012; 7:e46209. [PMID: 23049981 PMCID: PMC3458870 DOI: 10.1371/journal.pone.0046209] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2012] [Accepted: 08/29/2012] [Indexed: 12/21/2022] Open
Abstract
BACKGROUND Legionella pneumophila is a pathogenic bacterium that can cause Legionnaires' disease and other non-pneumonic infections in humans. This bacterium produces a pyomelanin pigment, a potential virulence factor with ferric reductase activity. In this work, we have investigated the role of phenylalanine hydroxylase from L. pneumophila (lpPAH), the product of the phhA gene, in the synthesis of the pyomelanin pigment and the growth of the bacterium in defined compositions. METHODOLOGY/PRINCIPAL FINDINGS Comparative studies of wild-type and phhA mutant corroborate that lpPAH provides the excess tyrosine for pigment synthesis. phhA and letA (gacA) appear transcriptionally linked when bacteria were grown in buffered yeast extract medium at 37°C. phhA is expressed in L. pneumophila growing in macrophages. We also cloned and characterized lpPAH, which showed many characteristics of other PAHs studied so far, including Fe(II) requirement for activity. However, it also showed many particular properties such as dimerization, a high conformational thermal stability, with a midpoint denaturation temperature (T(m)) = 79 ± 0.5°C, a high specific activity at 37°C (10.2 ± 0.3 µmol L-Tyr/mg/min) and low affinity for the substrate (K(m) (L-Phe) = 735 ± 50 µM. CONCLUSIONS/SIGNIFICANCE lpPAH has a major functional role in the synthesis of pyomelanin and promotes growth in low-tyrosine media. The high thermal stability of lpPAH might reflect the adaptation of the enzyme to withstand relatively high survival temperatures.
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Affiliation(s)
- Marte I. Flydal
- Department of Biomedicine, University of Bergen, Bergen, Norway
| | - Christa H. Chatfield
- Department of Microbiology-Immunology, Northwestern University Medical School, Chicago, Illinois, United States of America
| | - Huaixin Zheng
- Department of Microbiology-Immunology, Northwestern University Medical School, Chicago, Illinois, United States of America
| | - Felizza F. Gunderson
- Department of Microbiology-Immunology, Northwestern University Medical School, Chicago, Illinois, United States of America
| | - Oscar Aubi
- Department of Biomedicine, University of Bergen, Bergen, Norway
| | - Nicholas P. Cianciotto
- Department of Microbiology-Immunology, Northwestern University Medical School, Chicago, Illinois, United States of America
| | - Aurora Martinez
- Department of Biomedicine, University of Bergen, Bergen, Norway
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10
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Dictyostelium
phenylalanine hydroxylase is activated by its substrate phenylalanine. FEBS Lett 2012; 586:3596-600. [DOI: 10.1016/j.febslet.2012.09.008] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2012] [Revised: 09/08/2012] [Accepted: 09/10/2012] [Indexed: 11/20/2022]
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Ghai R, Falconer RJ, Collins BM. Applications of isothermal titration calorimetry in pure and applied research--survey of the literature from 2010. J Mol Recognit 2012; 25:32-52. [PMID: 22213449 DOI: 10.1002/jmr.1167] [Citation(s) in RCA: 117] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Isothermal titration calorimetry (ITC) is a biophysical technique for measuring the formation and dissociation of molecular complexes and has become an invaluable tool in many branches of science from cell biology to food chemistry. By measuring the heat absorbed or released during bond formation, ITC provides accurate, rapid, and label-free measurement of the thermodynamics of molecular interactions. In this review, we survey the recent literature reporting the use of ITC and have highlighted a number of interesting studies that provide a flavour of the diverse systems to which ITC can be applied. These include measurements of protein-protein and protein-membrane interactions required for macromolecular assembly, analysis of enzyme kinetics, experimental validation of molecular dynamics simulations, and even in manufacturing applications such as food science. Some highlights include studies of the biological complex formed by Staphylococcus aureus enterotoxin C3 and the murine T-cell receptor, the mechanism of membrane association of the Parkinson's disease-associated protein α-synuclein, and the role of non-specific tannin-protein interactions in the quality of different beverages. Recent developments in automation are overcoming limitations on throughput imposed by previous manual procedures and promise to greatly extend usefulness of ITC in the future. We also attempt to impart some practical advice for getting the most out of ITC data for those researchers less familiar with the method.
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Affiliation(s)
- Rajesh Ghai
- Institute for Molecular Bioscience (IMB), University of Queensland, St. Lucia, Queensland, 4072, Australia
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12
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Fitzpatrick PF. Allosteric regulation of phenylalanine hydroxylase. Arch Biochem Biophys 2012; 519:194-201. [PMID: 22005392 PMCID: PMC3271142 DOI: 10.1016/j.abb.2011.09.012] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2011] [Revised: 09/27/2011] [Accepted: 09/28/2011] [Indexed: 10/16/2022]
Abstract
The liver enzyme phenylalanine hydroxylase is responsible for conversion of excess phenylalanine in the diet to tyrosine. Phenylalanine hydroxylase is activated by phenylalanine; this activation is inhibited by the physiological reducing substrate tetrahydrobiopterin. Phosphorylation of Ser16 lowers the concentration of phenylalanine for activation. This review discusses the present understanding of the molecular details of the allosteric regulation of the enzyme.
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Affiliation(s)
- Paul F Fitzpatrick
- Department of Biochemistry and Center for Biomedical Neuroscience, University of Texas Health Science Center at San Antonio, TX 78229-3900, USA.
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