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Montioli R, Zamparelli C, Borri Voltattorni C, Cellini B. Oligomeric State and Thermal Stability of Apo- and Holo- Human Ornithine δ-Aminotransferase. Protein J 2017; 36:174-185. [PMID: 28345116 PMCID: PMC5432616 DOI: 10.1007/s10930-017-9710-5] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
Human ornithine δ-aminotransferase (hOAT) (EC 2.6.1.13) is a mitochondrial pyridoxal 5′-phosphate (PLP)-dependent aminotransferase whose deficit is associated with gyrate atrophy, a rare autosomal recessive disorder causing progressive blindness and chorioretinal degeneration. Here, both the apo- and holo-form of recombinant hOAT were characterized by means of spectroscopic, kinetic, chromatographic and computational techniques. The results indicate that apo and holo-hOAT (a) show a similar tertiary structure, even if apo displays a more pronounced exposure of hydrophobic patches, (b) exhibit a tetrameric structure with a tetramer-dimer equilibrium dissociation constant about fivefold higher for the apoform with respect to the holoform, and (c) have apparent Tm values of 46 and 67 °C, respectively. Moreover, unlike holo-hOAT, apo-hOAT is prone to unfolding and aggregation under physiological conditions. We also identified Arg217 as an important hot-spot at the dimer–dimer interface of hOAT and demonstrated that the artificial dimeric variant R217A exhibits spectroscopic properties, Tm values and catalytic features similar to those of the tetrameric species. This finding indicates that the catalytic unit of hOAT is the dimer. However, under physiological conditions the apo-tetramer is slightly less prone to unfolding and aggregation than the apo-dimer. The possible implications of the data for the intracellular stability and regulation of hOAT are discussed.
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Affiliation(s)
- Riccardo Montioli
- Department of Neuroscience, Biomedicine and Movement Sciences (Section of Biological Chemistry), University of Verona, Strada Le Grazie 8, 37134, Verona, Italy.
| | | | - Carla Borri Voltattorni
- Department of Neuroscience, Biomedicine and Movement Sciences (Section of Biological Chemistry), University of Verona, Strada Le Grazie 8, 37134, Verona, Italy
| | - Barbara Cellini
- Department of Neuroscience, Biomedicine and Movement Sciences (Section of Biological Chemistry), University of Verona, Strada Le Grazie 8, 37134, Verona, Italy
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Effects of interface mutations on the dimerization of alanine glyoxylate aminotransferase and implications in the mistargeting of the pathogenic variants F152I and I244T. Biochimie 2016; 131:137-148. [PMID: 27720751 DOI: 10.1016/j.biochi.2016.10.001] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2016] [Revised: 10/02/2016] [Accepted: 10/02/2016] [Indexed: 11/21/2022]
Abstract
In this work the dimerization process of the minor allelic form of human alanine glyoxylate aminotransferase, a pyridoxal 5'-phosphate enzyme, was investigated. Bioinformatic analyses followed by site-directed mutagenesis, size exclusion chromatography and catalytic activity experiments allowed us to identify Arg118, Phe238 and Phe240 as interfacial residues not essential for transaminase activity but important for dimer-monomer dissociation. The apo and the holo forms of the triple mutant R118A-Mi/F238S-Mi/F240S-Mi display a dimer-monomer equilibrium dissociation constant value at least ~260- and 31-fold larger, respectively, than the corresponding ones of AGT-Mi. In the presence of PLP, the apomonomer of the triple mutant undergoes a biphasic process: the fast phase represents the formation of an inactive PLP-bound monomer, while the slow phase depicts the monomer-monomer association that parallels the regain of transaminase activity. The latter events occur with a rate constant of ~0.02 μM-1min-1. In the absence of PLP, the apomonomer is also able to dimerize but with a rate constant value ~2700-fold lower. Thereafter, the possible interference with the dimerization process of AGT-Mi exerted by the mutated residues in the I244T-Mi and F152I-Mi variants associated with Primary Hyperoxaluria type 1 was investigated by molecular dynamics simulations. On the basis of the present and previous studies, a model for the dimerization process of AGT-Mi, I244T-Mi and F152I-Mi, which outlines the structural defects responsible for the complete or partial mistargeting of the pathogenic variants, was proposed and discussed.
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Oppici E, Montioli R, Dindo M, Maccari L, Porcari V, Lorenzetto A, Chellini S, Voltattorni CB, Cellini B. The Chaperoning Activity of Amino-oxyacetic Acid on Folding-Defective Variants of Human Alanine:Glyoxylate Aminotransferase Causing Primary Hyperoxaluria Type I. ACS Chem Biol 2015; 10:2227-36. [PMID: 26161999 DOI: 10.1021/acschembio.5b00480] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
The rare disease Primary Hyperoxaluria Type I (PH1) results from the deficit of liver peroxisomal alanine:glyoxylate aminotransferase (AGT), as a consequence of inherited mutations on the AGXT gene frequently leading to protein misfolding. Pharmacological chaperone (PC) therapy is a newly developed approach for misfolding diseases based on the use of small molecule ligands able to promote the correct folding of a mutant enzyme. In this report, we describe the interaction of amino-oxyacetic acid (AOA) with the recombinant purified form of two polymorphic species of AGT, AGT-Ma and AGT-Mi, and with three pathogenic variants bearing previously identified folding defects: G41R-Ma, G170R-Mi, and I244T-Mi. We found that for all these enzyme AOA (i) forms an oxime at the active site, (ii) behaves as a slow, tight-binding inhibitor with KI values in the nanomolar range, and (iii) increases the thermal stability. Furthermore, experiments performed in mammalian cells revealed that AOA acts as a PC by partly preventing the intracellular aggregation of G41R-Ma and by promoting the correct peroxisomal import of G170R-Mi and I244T-Mi. Based on these data, we carried out a small-scale screening campaign. We identified four AOA analogues acting as AGT inhibitors, even if only one was found to act as a PC. The possible relationship between the structure and the PC activity of these compounds is discussed. Altogether, these results provide the proof-of-principle for the feasibility of a therapy with PCs for PH1-causing variants bearing folding defects and provide the scaffold for the identification of more specific ligands.
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Affiliation(s)
- Elisa Oppici
- Department
of Life Sciences and Reproduction, Section of Biological Chemistry, University of Verona, Strada Le Grazie 8 37134 Verona, Italy
| | - Riccardo Montioli
- Department
of Life Sciences and Reproduction, Section of Biological Chemistry, University of Verona, Strada Le Grazie 8 37134 Verona, Italy
| | - Mirco Dindo
- Department
of Life Sciences and Reproduction, Section of Biological Chemistry, University of Verona, Strada Le Grazie 8 37134 Verona, Italy
| | - Laura Maccari
- Siena Biotech S.p.A., Strada
del Petriccio e Belriguardo, 35 53100 Siena, Italy
| | - Valentina Porcari
- Siena Biotech S.p.A., Strada
del Petriccio e Belriguardo, 35 53100 Siena, Italy
| | - Antonio Lorenzetto
- Department
of Life Sciences and Reproduction, Section of Biological Chemistry, University of Verona, Strada Le Grazie 8 37134 Verona, Italy
| | - Sara Chellini
- Siena Biotech S.p.A., Strada
del Petriccio e Belriguardo, 35 53100 Siena, Italy
| | - Carla Borri Voltattorni
- Department
of Life Sciences and Reproduction, Section of Biological Chemistry, University of Verona, Strada Le Grazie 8 37134 Verona, Italy
| | - Barbara Cellini
- Department
of Life Sciences and Reproduction, Section of Biological Chemistry, University of Verona, Strada Le Grazie 8 37134 Verona, Italy
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Serine hydroxymethyltransferase: A model enzyme for mechanistic, structural, and evolutionary studies. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2011; 1814:1489-96. [DOI: 10.1016/j.bbapap.2010.10.010] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/24/2010] [Revised: 10/25/2010] [Accepted: 10/29/2010] [Indexed: 11/18/2022]
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Mueller M, Nidetzky B. Orthophosphate binding at the dimer interface of Corynebacterium callunae starch phosphorylase: mutational analysis of its role for activity and stability of the enzyme. BMC BIOCHEMISTRY 2010; 11:8. [PMID: 20113461 PMCID: PMC2837607 DOI: 10.1186/1471-2091-11-8] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/09/2009] [Accepted: 01/29/2010] [Indexed: 11/30/2022]
Abstract
Background Orthophosphate recognition at allosteric binding sites is a key feature for the regulation of enzyme activity in mammalian glycogen phosphorylases. Protein residues co-ordinating orthophosphate in three binding sites distributed across the dimer interface of a non-regulated bacterial starch phosphorylase (from Corynebacterium callunae) were individually replaced by Ala to interrogate their unknown function for activity and stability of this enzyme. Results While the mutations affected neither content of pyridoxal 5'-phosphate cofactor nor specific activity in phosphorylase preparations as isolated, they disrupted (Thr28→Ala, Arg141→Ala) or decreased (Lys31→Ala, Ser174→Ala) the unusually strong protective effect of orthophosphate (10 or 100 mM) against inactivation at 45°C and subunit dissociation enforced by imidazole, as compared to wild-type enzyme. Loss of stability in the mutated phosphorylases appeared to be largely due to weakened affinity for orthophosphate binding. Binding of sulphate mimicking the crystallographically observed "non-covalent phosphorylation" of the phosphorylase at the dimer interface did not have an allosteric effect on the enzyme activity. Conclusions The phosphate sites at the subunit-subunit interface of C. callunae starch phosphorylase appear to be cooperatively functional in conferring extra kinetic stability to the native dimer structure of the active enzyme. The molecular strategy exploited for quaternary structure stabilization is to our knowledge novel among dimeric proteins. It can be distinguished clearly from the co-solute effect of orthophosphate on protein thermostability resulting from (relatively weak) interactions of the ligand with protein surface residues.
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Affiliation(s)
- Mario Mueller
- Institute of Biotechnology and Biochemical Engineering, Graz University of Technology, Petersgasse 12, A-8010 Graz, Austria
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Florio R, Chiaraluce R, Consalvi V, Paiardini A, Catacchio B, Bossa F, Contestabile R. Structural stability of the cofactor binding site in Escherichia coli serine hydroxymethyltransferase - the role of evolutionarily conserved hydrophobic contacts. FEBS J 2009; 276:7319-28. [DOI: 10.1111/j.1742-4658.2009.07442.x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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