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Deu E, Kirsch JF. Engineering homooligomeric proteins to detect weak intersite allosteric communication: aminotransferases, a case study. Protein Sci 2011; 20:1991-2003. [PMID: 21936010 DOI: 10.1002/pro.741] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2011] [Revised: 09/08/2011] [Accepted: 09/12/2011] [Indexed: 11/11/2022]
Abstract
The existence of low levels of intersubunit communication in homooligomeric enzymes is often difficult to discover, as the identical active sites cannot be probed individually to dissect their interdependent contributions. The homodimeric paralogs, E. coli aspartate- (AATase) and tyrosine aminotransferase (TATase), have not been demonstrated to show allostery. To address this question, we engineered a hybrid aminotransferase containing two distinct catalytic pockets: an AATase and a TATase site. The TATase/AATase hybrid was constructed by grafting an engineered TATase active site into one of the catalytic pockets of E. coli AATase. Each active site conserves its specific catalytic and inhibitor binding properties, and the hybrid catalyzes simultaneously each aminotransferase reaction at the respective site. Importantly, association of a selective inhibitor into one of the catalytic pockets decreases the activity of the second active site by up to 25%, thus proving unequivocally the existence of allosteric communication between active sites. The procedure may be applicable to other homologous sets of enzymes.
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Affiliation(s)
- Edgar Deu
- Department of Pathology, Stanford University School of Medicine, Stanford, California 94305-5324, USA
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2
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Artigues A, Iriarte A, Martinez-Carrion M. Refolding intermediates of acid-unfolded mitochondrial aspartate aminotransferase bind to hsp70. J Biol Chem 1997; 272:16852-61. [PMID: 9201992 DOI: 10.1074/jbc.272.27.16852] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
The cytosolic (cAAT) and mitochondrial (mAAT) isozymes of eukaryotic aspartate aminotransferase share a high degree of sequence identity and almost identical three-dimensional structure. The rat liver proteins can be refolded and reassembled into active dimers after unfolding at low pH. However, refolding of the mitochondrial form after unfolding at pH 2.0 is arrested in the presence of hsp70, whereas this chaperone does not affect the refolding of the cytosolic isozyme unfolded under similar conditions. To elucidate the nature of the differential interaction between hsp70 and the two transaminase forms, we have characterized their refolding from their acid-unfolded states. The recovery of activity of the cytosolic enzyme is monophasic and can be adequately described by a single first-order reaction. By contrast, two sequential first-order rate-limiting steps can be detected for the refolding and reactivation of the mitochondrial protein. The overall refolding pathway of mAAT includes a very fast collapse to an intermediate with 80% of the secondary structure of the active dimer. This is followed by a slow isomerization to form assembly-competent monomers that rapidly associate to form an inactive dimer and a final structural rearrangement of the dimer to the native conformation. Analysis of the interaction of hsp70 with intermediates along the folding pathway of mAAT shows that the polypeptide loses its ability to bind to the chaperone after it has proceeded through the first isomerization/fast dimerization steps. Thus it appears that only the first collapsed intermediate states in the folding of mAAT bind hsp70. By contrast a faster refolding of cAAT from this collapsed state could explain, at least in part, the inability of hsp70 to bind this isozyme.
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Affiliation(s)
- A Artigues
- Division of Molecular Biology and Biochemistry, School of Biological Sciences, University of Missouri-Kansas City, Kansas City, Missouri 64110-2499, USA
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3
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Refolding of the precursor and mature forms of mitochondrial aspartate aminotransferase after guanidine hydrochloride denaturation. J Biol Chem 1993. [DOI: 10.1016/s0021-9258(18)41526-8] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
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Sanchez-Ruiz JM, Iriarte A, Martinez-Carrion M. The ionization states of the 5'-phosphate group in the various coenzyme forms bound to mitochondrial aspartate aminotransferase. Arch Biochem Biophys 1991; 286:38-45. [PMID: 1897957 DOI: 10.1016/0003-9861(91)90006-5] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
We have carried out a Fourier transform infrared spectroscopic study of mitochondrial aspartate aminotransferase in the spectral region where phosphate monoesters give rise to absorption. Infrared spectra in the above-mentioned region are dominated by protein absorption. Yet, below 1020 cm-1 protein interferences are minor, permitting the detection of the band arising from the symmetric stretching of dianionic phosphate monoesters [T. Shimanouchi, M. Tsuboi, and Y. Kyogoku (1964) Adv. Chem. Phys. 8, 435-498]. The integrated intensity of this band in several enzyme forms (pyridoxal phosphate, pyridoxamine phosphate, and sodium borohydride-reduced, pyridoxyl phosphate form) does not change with pH in the range 5-9. This behavior contrasts that of free pyridoxal phosphate (PLP) and pyridoxamine phosphate (PMP) in solution, where the dependence of the same infrared band intensity with pH can be correlated to the known pK values for the 5'-phosphate ester in solution. The integrated intensity value of this infrared band for the PLP enzyme form before and after reduction with sodium borohydride is close to that given by free PLP at pH 8-9. These results are taken as evidence that in the active site of mitochondrial aspartate aminotransferase the 5'-phosphate group of PLP remains mostly dianionic even at a pH near 5. Thus, it is suggested that the chemical shift changes associated with pH titrations of various PLP forms reported in a previous 31P NMR study of this enzyme [M. E. Mattingly, J. R. Mattingly, and M. Martinez-Carrion (1982) J. Biol. Chem. 257, 8872] are due to the fact that the phosphorus chemical shift senses the O-P-O bond distortions induced by the ionization of a nearby residue. Since no chemical shift changes were observed in pH titrations of the PMP forms (lacking an ionizable internal aldimine) of this isozyme, the Schiff base between PLP and Lys-258 at the active site is the most likely candidate for the ionizing group influencing the phosphorus chemical shift in this enzyme.
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Affiliation(s)
- J M Sanchez-Ruiz
- Division of Molecular Biology and Biochemistry, School of Basic Life Sciences, University of Missouri-Kansas City 64110-2499
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Iriarte A, Farach HA, Martinez-Carrion M. Coenzyme active site occupancy as an indicator of independence of the subunits of mitochondrial aspartate aminotransferase. J Biol Chem 1984. [DOI: 10.1016/s0021-9258(17)39829-0] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
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Abstract
Aminotransferases are ubiquitous enzymes of mammalian cells and several are of important diagnostic use. The application of aspartate aminotransferase activity measurements in serum from individuals suffering from myocardial infarction brought about a new dimension in clinical laboratory testing in the 1950s. This review focuses on measurement techniques for aspartate aminotransferase and their application (a subsequent article will review other aminotransferases). Assay techniques measuring enzyme activity are direct spectrophotometric measurements, manometric techniques, assays using dye substances, coupled enzyme techniques, and radiometric procedures. Of these procedures, the one employing malate dehydrogenase and NADH is the most important and is covered in particular detail. The estimation of the mitochondrial isoenzyme of aspartate aminotransferase is also of clinical interest, in particular for estimating severity of disease or in specific applications (e.g., chronic alcoholism). Methods reviewed for estimation of this enzyme are electrophoresis, chromatography, differential kinetic behavior, and immunochemical separation. Determination of the enzyme protein by techniques independent of its catalytic activity are also reviewed.
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Properties of the active site lysyl residue of mitochondrial aspartate aminotransferase in solution. J Biol Chem 1983. [DOI: 10.1016/s0021-9258(18)32398-6] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
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8
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Kirsten H, Gehring H, Christen P. Crystalline aspartate aminotransferase: lattice-induced functional asymmetry of the two subunits. Proc Natl Acad Sci U S A 1983; 80:1807-10. [PMID: 6572940 PMCID: PMC393698 DOI: 10.1073/pnas.80.7.1807] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Abstract
The enzymic activity of crystalline mitochondrial aspartate aminotransferase (L-aspartate:2-oxoglutarate aminotransferase, EC 2.6.1.1) was determined in suspensions of noncrosslinked microcrystals in 30% (wt/vol) polyethylene glycol. The crystals (average dimensions, 22 x 5 x 0.8 micron) were small enough to preclude diffusional rate limitation. They had the same habit as the triclinic crystals used for the determination of the spatial structure of the enzyme by x-ray crystallographic analysis [Ford, G. C., Eichele, G., and Jansonius, J. N. (1980) Proc. Natl. Acad. Sci. USA 77, 2559-2563]. Determination of the Michaelis-Menten parameters showed that the packing of the enzyme dimer into the crystal lattice not only decreases its activity but also induces a functional nonequivalence of the two subunits that behave identically in solution. The crystalline enzyme possesses a high-affinity subunit with Km values similar to those of the enzyme in solution (K'm = 0.5 mM for aspartate and 1.2 mM for 2-oxoglutarate) and a low-affinity subunit (K'm = 5.5 mM and 14.5 mM, respectively). The catalytic activity of the high-affinity subunit is 3% and that of the low-affinity subunit is 15% of the activity of the enzyme in solution. The functional asymmetry of the crystalline enzyme dimer could also be demonstrated by selective mechanism-based modification of either type of active sites. In view of the apparently identical conformation of the two subunits in the crystalline enzyme, its decreased catalytic efficiency and its functional asymmetry likely are due to constraints exerted by the crystal lattice on the conformational adaptability of the two subunits. In triclinic crystals the two subunits of the enzyme dimer have dissimilar lattice contacts.
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9
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31P nuclear magnetic resonance of mitochondrial aspartate aminotransferase. The effects of solution pH and ligand binding. J Biol Chem 1982. [DOI: 10.1016/s0021-9258(18)34211-x] [Citation(s) in RCA: 31] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
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10
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Arrio-Dupont M, Vergé D. Binding of substrates to aspartate aminotransferase. Evidence for a dissymmetrical binding. EUROPEAN JOURNAL OF BIOCHEMISTRY 1982; 125:183-7. [PMID: 7106120 DOI: 10.1111/j.1432-1033.1982.tb06666.x] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
The binding of substrates L-glutamate and 2-oxoglutarate to aspartate aminotransferase was studied by spectrophotometric titration according to Jenkins and D'Ari [J. Biol. Chem. 241 (1966) 2845-2854]. Our data, obtained over a wide range of substrate concentrations, were not consistent with the hypothesis of independent and equivalent binding sites. Two other possibilities were considered: (a) the sites are independent but not equivalent; (b) a negative cooperativity occurs between the sites. It is possible to distinguish between these two hypotheses because the substrate binding is complex, with a couple of substrates and two forms of enzyme in equilibrium with the enzyme-substrate complexes. Distinct equations delta A/Et=f[substrates], where delta A = change in absorbance upon addition of substrates to the enzyme and Et = total site concentration, were derived for each case. The data were directly fitted to these equations by an iterative multilinear regression analysis, and the equilibrium constants were computed. This analysis showed that the binding sites are independent and not equivalent, with dissociation constants for 2-oxoglutarate of 2 micro M and 280 micro M and dissociation constants for glutamate of 1.7 mM and 22 mM. The molar absorption coefficient of the binary complexes is 2250 M-1 cm-1.
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11
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Sandmeier E, Christen P. Chemical modification of a functional arginyl residue (Arg 292) of mitochondrial aspartate aminotransferase. Identification as the binding site for the distal carboxylate group of the substrate. J Biol Chem 1982. [DOI: 10.1016/s0021-9258(18)34493-4] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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12
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Arrio-Dupont M, Vergé D. Functional interactions between subunits of aspartate aminotransferase. Formation of monoliganded dimers during titration of the apoenzyme by pyridoxal 5'-phosphate. J Mol Biol 1982; 157:383-94. [PMID: 7108963 DOI: 10.1016/0022-2836(82)90241-8] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
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13
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Balk H, Frank A, Bartholmes P, Jaenicke R. Equilibrium and kinetic measurements of the binding of pyridoxal 5'-phosphate to hybrid tryptophan synthase from Escherichia coli. EUROPEAN JOURNAL OF BIOCHEMISTRY 1981; 121:105-12. [PMID: 7035165 DOI: 10.1111/j.1432-1033.1981.tb06437.x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
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14
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Vergé D, Arrio-Dupont M. A rapid preparation of the apo-holo hybrid of aspartate aminotransferase. FEBS Lett 1981; 130:39-42. [PMID: 7286224 DOI: 10.1016/0014-5793(81)80660-6] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
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15
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Eichele G, Ford GC, Glor M, Jansonius JN, Mavrides C, Christen P. The three-dimensional structure of mitochondrial aspartate aminotransferase at 4.5 A resolution. J Mol Biol 1979; 133:161-80. [PMID: 529281 DOI: 10.1016/0022-2836(79)90255-9] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
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16
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Arrio-Dupont M, Coulet PR. Aspartate aminotransferase immobilized on collagen films. Activity of dissociated subunits. Biochem Biophys Res Commun 1979; 89:345-52. [PMID: 486166 DOI: 10.1016/0006-291x(79)90636-3] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
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17
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Borisov VV, Borisova SN, Kachalova GS, Sosfenov NI, Vainshtein BK, Torchinsky YM, Braunstein AE. Three-dimensional structure at 5 A resolution of cytosolic aspartate transaminase from chicken heart. J Mol Biol 1978; 125:275-92. [PMID: 731696 DOI: 10.1016/0022-2836(78)90403-5] [Citation(s) in RCA: 40] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
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18
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Magnetic resonance relaxation rates in the study of complexes of ligands with spin-labeled aspartate transaminase. J Biol Chem 1978. [DOI: 10.1016/s0021-9258(17)30437-4] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
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Schlegel H, Christen P. Cytosolic aspartate aminotransferase. Studies on subunit interactions with the apo/holo hybrid dimer. BIOCHIMICA ET BIOPHYSICA ACTA 1978; 532:6-16. [PMID: 620057 DOI: 10.1016/0005-2795(78)90442-7] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
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20
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21
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Schlegel H, Zaoralek PE, Christen P. Aspartate aminotransferase. Determination of the active site occupancy pattern indicates independent transamination of the two subunits. J Biol Chem 1977. [DOI: 10.1016/s0021-9258(17)40098-6] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
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22
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Haddad LC, Thayer WS, Jenkins WT. Solvent interactions with the active site of the pig heart cytosolic aspartate aminotransferase. Arch Biochem Biophys 1977; 181:66-72. [PMID: 18112 DOI: 10.1016/0003-9861(77)90484-2] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
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23
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Critz WJ, Martinez-Carrion M. Fluorine-19 nuclear magnetic resonance studies of effects of ligands on trifluoroacetonylated supernatant aspartate transaminase. Biochemistry 1977; 16:1559-64. [PMID: 15584 DOI: 10.1021/bi00627a005] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
The selective reaction of Cys-45 and -82, on the one hand, and Cys-390, on the other, with 3-bromo-1,1,1-trifluoropropanone allows for the probing of these regions of aspartate transaminase in the absence and in the presence of enzymatic ligands by 19F nuclear magnetic resonance (NMR). The 19F chemical shifts of the resonance lines differ for the three cysteines and so does their behavior with pH changes. The resonance signals with chemical shifts at 615 and 800 Hz upfield from trifluoroacetic acid correspond to modified cysteine-82 and -45 and have tentatively been assigned in this order. The 615-Hz resonance is affected by pH changes that fit best the influence of a single ionizing residue. On the 800-Hz line, the pH changes appear to be the influence of a minimum of two ionizing residues. The 19F resonance from modified Cys-390 is pH independent in the pH range 5-9 for the pyridoxal phosphate, pyridoxamine phosphate, and apoenzyme forms of the enzyme. Occupation of the active site by a quasi-enzyme-substrate complex, trifluoromethionine pyridoxyl phosphate, affects the 19F chemical shift of modified Cys-390, making it pH dependent with a pK value of 8.4. The 19F NMR properties of the pyridoxal form of Cys-390-modified enzyme can be used to monitor some ligand interactions with the active-center region. Addition of alpha-ketoglutarate or succinate to the ketone labeled enzyme causes a decrease in the resonance line width, and titrations show that this procedure is a good method with which to study the affinity of the enzyme for these ligands. The interpretation of the chemical shift and line-width characteristics of the 19F resonance arising from Cys-390 are most consistent with a model in which the region around this residue seems to be affected by conformational changes arising from substrate binding to the active-center subsites in productive (covalent) manner. Nonproductive complexes which possess fast ligand-protein exchange, such as those between alpha-ketoglutarate or succinate with the pyridoxal phosphate form of the enzyme, may result only in a greater degree of freedom for Cys-390.
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Martinez-Carrion M, Slebe JC, Boettcher B, Relimpio AM. Fluorine-19 as a covalent active site-directed magnetic resonance probe in aspartate transaminase. J Biol Chem 1976. [DOI: 10.1016/s0021-9258(17)33626-8] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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Martinez-Carrion M, Boettcher B. Fluorescence energy transfer between active sites in aspartate transaminase. Biochem Biophys Res Commun 1975; 67:1480-7. [PMID: 1201098 DOI: 10.1016/0006-291x(75)90193-x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
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