Emil H. Harutyunyan

Lomonosov Moscow State University, Moskva, Moscow, Russia

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Publications (25)76.16 Total impact

  • [Show abstract] [Hide abstract] ABSTRACT: The three-dimensional structures of four mutant E. coli inorganic pyrophosphatases (PPases) with single Asp-->Asn substitutions at positions 42, 65, 70, and 97 were solved at 1.95, 2.15, 2.10, and 2.20 A resolution, respectively. Asp-42-->Asn and Asp-65-->Asn mutant PPases were prepared as complexes with sulfate--a structural analog of phosphate, the product of enzymatic reaction. A comparison of mutant enzymes with native PPases revealed that a single amino acid substitution changes the position of the mutated residue as well as the positions of several functional groups and some parts of a polypeptide chain. These changes are responsible for the fact that mutant PPases differ from the native ones in their catalytic properties. The sulfate binding to the mutant PPase active site causes molecular asymmetry, as shown for the native PPase earlier. The subunit asymmetry is manifested in different positions of sulfate and several functional groups, as well as changes in packing of hexamers in crystals and in cell parameters.
    No preview · Article · Jul 1998 · Biochemistry (Moscow)
  • [Show abstract] [Hide abstract] ABSTRACT: The three-dimensional structures of E. coli inorganic pyrophosphatase (PPase) and its complexes with Mn2+ in a high affinity site and with Mg2+ in high and low affinity sites determined by authors in 1994-1996 at 1.9-2.2 A resolution are compared. Metal ion binding initiates the shifts of alpha-carbon atoms and of functional groups and rearrangement of non-covalent interaction system of hexameric enzyme molecule. As a result, the apoPPase with six equal subunits turns after Mg2+ binding into the structure with three types of subunits distinguished by structure and occupance of the low affinity Mg2+ site. Induced asymmetry reflects the subunit interactions and cooperativity between Mg2+ binding sites. These molecular rearrangements are structural basis to account for special features of the enzyme behavior and to propose one of the pathways for enzymatic activity regulation of constitutive PPases in vivo.
    No preview · Article · Jun 1998 · Biochemistry (Moscow)
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    [Show abstract] [Hide abstract] ABSTRACT: The X-ray structure of tryptophanase (Tnase) reveals the interactions responsible for binding of the pyridoxal 5'-phosphate (PLP) and atomic details of the K+ binding site essential for catalysis. The structure of holo Tnase from Proteus vulgaris (space group P2(1)2(1)2(1) with a = 115.0 A, b = 118.2 A, c = 153.7 A) has been determined at 2.1 A resolution by molecular replacement using tyrosine phenol-lyase (TPL) coordinates. The final model of Tnase, refined to an R-factor of 18.7%, (Rfree = 22.8%) suggests that the PLP-enzyme from observed in the structure is a ketoenamine. PLP is bound in a cleft formed by both the small and large domains of one subunit and the large domain of the adjacent subunit in the so-called "catalytic" dimer. The K+ cations are located on the interface of the subunits in the dimer. The structure of the catalytic dimer and mode of PLP binding in Tnase resemble those found in aspartate amino-transferase, TPL, omega-amino acid pyruvate aminotransferase, dialkylglycine decarboxylase (DGD), cystathionine beta-lyase and ornithine decarboxylase. No structural similarity has been detected between Tnase and the beta 2 dimer of tryptophan synthase which catalyses the same beta-replacement reaction. The single monovalent cation binding site of Tnase is similar to that of TPL, but differs from either of those in DGD.
    Full-text · Article · Feb 1998 · Journal of Molecular Biology
  • [Show abstract] [Hide abstract] ABSTRACT: Crystalline holo inorganic pyrophosphatase from Escherichia coli was grown in the presence of 250 mM MgCl2. The crystal structure has been solved by Patterson search techniques and refined to an R-factor of 17.6% at 1.9 A resolution. The upper estimate of the root-mean-square error in atomic positions is 0.26 A. These crystals belong to space group P3(2)21 with unit cell dimensions a = b = 110.27 A and c = 78.17 A. The asymmetric unit contains a trimer of subunits, i.e., half of the hexameric molecule. In the central cavity of the enzyme molecule, three Mg2+ ions, each shared by two subunits of the hexamer, are found. In the active sites of two crystallographically independent subunits, two Mg2+ ions are bound. The second active site Mg2+ ion is missing in the third subunit. A mechanism of catalysis is proposed whereby a water molecule activated by a Mg2+ ion and Tyr 55 play essential roles.
    No preview · Article · Jul 1997 · Biochemistry
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    [Show abstract] [Hide abstract] ABSTRACT: The three-dimensional structure of inorganic pyrophosphatase from Escherichia coli complexed with sulfate was determined at 2.2 A resolution using Patterson's search technique and refmed to an R-factor of 19.2%. Sulfate may be regarded as a structural analog of phosphate, the product of the enzyme reaction, and as a structural analog of methyl phosphate, the irreversible inhibitor. Sulfate binds to the pyrophosphatase active site cavity as does phosphate and this diminishes molecular symmetry, converting the homohexamer structure form (alpha3)2 into alpha3'alpha3". The asymmetry of the molecule is manifested in displacements of protein functional groups and some parts of the polypeptide chain and reflects the interaction of subunits and their cooperation. The significance of re-arrangements for pyrophosphatase function is discussed.
    Full-text · Article · Jul 1997 · FEBS Letters
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    [Show abstract] [Hide abstract] ABSTRACT: Aspartic acids 65, 67, 70, 97 and 102 in the inorganic pyrophosphatase of Escherichia coli, identified as evolutionarily conserved residues of the active site, have been replaced by asparagine. Each mutation was found to decrease the k(app) value by approx. 2-3 orders of magnitude. At the same time, the Km values changed only slightly. Only minor changes take place in the pK values of the residues essential for both substrate binding and catalysis. All mutant variants have practically the same affinity to Mg2+ as the wild-type pyrophosphatase.
    Full-text · Article · Jan 1997 · FEBS Letters
  • [Show abstract] [Hide abstract] ABSTRACT: Haemoglobins have the ability to discriminate between oxygen and other diatomic molecules. To further understanding of this process the X-ray crystal structures of carbonmonoxy and nitrosyl-leghaemoglobin have been determined at 1.8 A resolution. The ligand geometry is discussed in detail and the controversial issue of bent versus linear carbon monoxide binding is addressed. The bond angle of 160 degrees for CO-leghaemoglobin is in conflict with recent spectroscopy results on myoglobin but is consistent with angles obtained for myoglobin X-ray crystal structures. In contrast to the numerous carbon monoxide studies, very little stereochemical information is available for the nitric oxide adduct of haemoglobin. This is provided by the X-ray structure of NO-leghaemoglobin, which conforms to expected geometry with an Fe-NO angle of 147 degrees and a lengthened iron-proximal histidine bond. Thus crystallographic evidence is given for the predicted weakening of this bond on the binding of nitric oxide.
    No preview · Article · Dec 1996 · Journal of Molecular Biology
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    [Show abstract] [Hide abstract] ABSTRACT: The three-dimensional structure of the manganese-phosphate complex of inorganic pyrophosphatase from Saccharomyces cerevisiae has been refined to an R factor of 19.0% at 2.4-A resolution. X-ray data were collected from a single crystal using an imaging plate scanner and synchrotron radiation. There is one dimeric molecule in the asymmetric unit. The upper estimate of the root-mean-square coordinate error is 0.4 A using either the delta A plot or the superposition of the two crystallographically independent subunits. The good agreement between the coordinates of the two subunits, which were not subjected to non-crystallographic symmetry restraints, provides independent validation of the structure analysis. The active site in each subunit contains four manganese ions and two phosphates. The manganese ions are coordinated by the side chains of aspartate and glutamate residues. The phosphate groups, which were identified on the basis of their local stereochemistry, interact either directly or via water molecules with manganese ions and lysine, arginine, and tyrosine side chains. The phosphates are bridged by two of the manganese ions. The outer phosphate is exposed to solvent. The inner phosphate is surrounded by all four manganese ions. The ion-binding sites are related to the order of binding previously established from kinetic studies. A hypothesis for the transition state of the catalytic reaction is put forward.
    Full-text · Article · Aug 1996 · European Journal of Biochemistry
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    B. Vainshtein · E. Harutyunyan · I. Kuranova · V. Lamzyn · Z. Dauter · K. Wilson
    Full-text · Article · Aug 1996 · Acta Crystallographica Section A Foundations of Crystallography
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    [Show abstract] [Hide abstract] ABSTRACT: Further refinement of X-ray data on Escherichia coli inorganic pyrophosphatase [Oganessyan et al. (1994) FEBS Lett. 348, 301-304] to 2.2 A reveals a system of noncovalent interactions involving Tyr55 and Tyr141 in the active site. The pKa for one of the eight Tyr residues in wild-type pyrophosphatase is as low as 9.1 and further decreases to 8.1 upon Mg2+ binding, generating characteristic changes in the absorption spectrum. These effects are lost in a Y55F but not in a Y141F variant. It is suggested that the lower-affinity site for Mg2+ in the enzyme is formed by Tyr55 and Asp70, which are in close proximity in the apo-enzyme structure.
    Full-text · Article · Jan 1996 · FEBS Letters
  • [Show abstract] [Hide abstract] ABSTRACT: The leghaemoglobins have oxygen affinities 11 to 24 times higher than that of sperm whale myoglobin, due mainly to higher rates of association. To find out why, we have determined the structures of deoxy- and oxy-leghaemoglobin II of the lupin at 1.7 Å resolution. Results confirm the general features found in previous X-ray analyses of this protein. The unique feature that has now emerged is the rotational freedom of the proximal histidine. In deoxy-leghaemoglobin the imidazole oscillates between two alternative orientations, eclipsing either the lines to 0.32 Å from the mean porphyrin plane.
    No preview · Article · Aug 1995 · Journal of Molecular Biology
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    [Show abstract] [Hide abstract] ABSTRACT: An E. coli inorganic pyrophosphatase overproducer and a method for a large-scale production of the homogeneous enzyme are described. The inorganic pyrophosphatase was crystallized in the form containing one subunit of a homohexameric molecule per asymmetric unit: space group R32, a = 110.4 A, c = 76.8 A. The electron density map to 2.5 A resolution phased with Eu- and Hg-derivatives (figure of merit, = 0.51) was improved by the solvent flattening procedure ( = 0.77). The course of the polypeptide chain and the secondary structure elements, intersubunit contacts and positions of the active sites were characterized. Homology with S. cerevisiae inorganic pyrophosphatase structure was found.
    Full-text · Article · Aug 1994 · FEBS Letters
  • [Show abstract] [Hide abstract] ABSTRACT: Three-dimensional crystal structures of holo (ternary complex enzyme-NAD-azide) and apo NAD-dependent dimeric formate dehydrogenase (FDH) from the methylotrophic bacterium Pseudomonas sp. 101 have been refined to R factors of 11.7% and 14.8% at 2.05 and 1.80 A resolution, respectively. The estimated root-mean-square error in atomic co-ordinates is 0.11 A for holo and 0.18 A for apo. X-ray data were collected from single crystals using an imaging plate scanner and synchrotron radiation. In both crystal forms there is a dimer in the asymmetric unit. Both structures show essentially 2-fold molecular symmetry. NAD binding causes movement of the catalytic domain and ordering of the C terminus, where a new helix appears. This completes formation of the enzyme active centre in holo FDH. NAD is bound in the cleft separating the domains and mainly interacts with residues from the co-enzyme binding domain. In apo FDH these residues are held in essentially the same conformation by water molecules occupying the NAD binding region. An azide molecule is located near the point of catalysis, the C4 atom of the nicotinamide moiety of NAD, and overlaps with the proposed formate binding site. There is an extensive channel running from the active site to the protein surface and this is supposed to be used by substrate to reach the active centre after NAD has already bound. The structure of the active site and a hypothetical catalytic mechanism are discussed. Sequence homology of FDH with other NAD-dependent formate dehydrogenases and some D-specific dehydrogenases is discussed on the basis of the FDH three-dimensional structure.
    No preview · Article · Mar 1994 · Journal of Molecular Biology
  • [Show abstract] [Hide abstract] ABSTRACT: Crystals of Proteus vulgaris holotryptophanase have been grown by the hanging-drop technique using polyethylene glycol 4000 as precipitant in the presence of monovalent cations K+ or Cs+. Orthorhombic crystals (P2(1)2(1)2(1)) grown with Cs+ have unit cell parameters a = 115.0 A, b = 118.2 A and c = 153.7 A and diffract to 1.8 A. There are four subunits of the tetrameric molecule in the asymmetric unit. Native data have been collected to 2.5 A resolution. The 3.4 A data were collected from tetragonal crystals of Escherichia coli holotryptophanase grown under conditions described by Kawata et al. (1991). The molecular replacement solution for this crystal form has been found using tyrosine phenol-lyase coordinates. The correct enantiomorph is P4(3)2(1)2. There are two subunits in the asymmetric unit.
    No preview · Article · Feb 1994 · Journal of Molecular Biology
  • [Show abstract] [Hide abstract] ABSTRACT: The structural protein, gene product 9 (gp9), of bacteriophage T4 controls baseplate expansion at the first steps of virus attachment onto its host bacterial cell with subsequent tail contraction. Gp9, which has an M(r) of 30.8 kDa and contains 287 amino acids, has been purified from a recombinant Escherichia coli strain and crystallized at 25 degrees C using the hanging drop vapor diffusion method at pH 4.0 with ammonium sulfate as precipitant. The crystals of gp9 belong to the space group R32 with hexagonal cell dimensions a = b = 86.5 A and c = 156.2 A and diffract X-rays to at least 2.7 A. There is one molecule per asymmetric unit.
    No preview · Article · Dec 1993 · Journal of Molecular Biology
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    [Show abstract] [Hide abstract] ABSTRACT: Tyrosine phenol-lyase (EC from Citrobacter freundii has been cloned and the primary sequence deduced from the DNA sequence. From the BrCN digest of the NaBH4-reduced holoenzyme, five peptides were purified and sequenced. The amino acid sequences of the peptides agreed with the corresponding parts of the tyrosine phenol-lyase sequence obtained from the gene structure. K257 is the pyridoxal 5'-phosphate binding residue. Assisted by the sequence data, the crystal structure of apotyrosine phenol-lyase, a pyridoxal 5'-phosphate-dependent enzyme, has been refined to an R-factor of 16.2% at 2.3-A resolution using synchrotron radiation diffraction data. The tetrameric molecule has 222 symmetry, with one of the axes coincident with the crystallographic 2-fold symmetry axis of the crystal which belongs to the space group P2(1)2(1)2 with a = 76.0 A, b = 138.3 A, and c = 93.5 A. Each subunit comprises 14 alpha-helices and 16 beta-strands, which fold into a small and a large domain. The coenzyme-binding lysine residue is located at the interface between the large and small domains of one subunit and the large domain of a crystallographically related subunit. The fold of the large, pyridoxal 5'-phosphate binding domain and the location of the active site are similar to that found in aminotransferases. Most of the residues which participate in binding of pyridoxal 5'-phosphate in aminotransferases are conserved in the structure of tyrosine phenol-lyase. Two dimers of tyrosine phenol-lyase, each of which has a domain architecture similar to that found in aspartate aminotransferases, are bound together through a hydrophobic cluster in the center of the molecule and intertwined N-terminal arms.
    Full-text · Article · May 1993 · Biochemistry
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    [Show abstract] [Hide abstract] ABSTRACT: The ternary complex of NAD-dependent formate dehydrogenase (FDH) from the methylotrophic bacterium Pseudomonas sp. 101 (enzyme-NAD-azide) has been crystallised in the space group P2(1)2(1)2(1) with cell dimensions a = 11.60 nm, b = 11.33 nm, c = 6.34 nm. There is 1 dimeric molecule/asymmetric unit. An electron density map was calculated using phases from multiple isomorphous replacement at 0.30 nm resolution. Four heavy atom derivatives were used. The map was improved by solvent flattening and molecular averaging. The atomic model, including 2 x 393 amino acid residues, was refined by the CORELS and PROLSQ packages using data between 1.0 nm and 0.30 nm excluding structure factors less than 1 sigma. The current R factor is 27.1% and the root mean square deviation from ideal bond lengths is 4.2 pm. The FDH subunit is folded into a globular two-domain (coenzyme and catalytic) structure and the active centre and NAD binding site are situated at the domain interface. The beta sheet in the FDH coenzyme binding domain contains an additional beta strand compared to other dehydrogenases. The difference in quaternary structure between FDH and the other dehydrogenases means that FDH constitutes a new subfamily of NAD-dependent dehydrogenases: namely the P-oriented dimer. The FDH nucleotide binding region of the structure is aligned with the three dimensional structures of four other dehydrogenases and the conserved residues are discussed. The amino acid residues which contribute to the active centre and which make contact with NAD have been identified.
    Full-text · Article · Jul 1992 · European Journal of Biochemistry
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    [Show abstract] [Hide abstract] ABSTRACT: The tyrosine phenol lyase (EC from Citrobacter intermedius has been crystallised in the apo form by vapour diffusion. The space group is P2(1)2(1)2. The unit cell has dimensions a = 76.0 A, b = 138.3 A, c = 93.5 A and it contains two subunits of the tetrameric molecule in the asymmetric unit. Diffraction data for the native enzyme and two heavy atom derivatives have been collected with synchrotron radiation and an image plate scanner. The structure has been solved at 2.7 A resolution by isomorphous replacement with subsequent modification of the phases by averaging the density around the non-crystallographic symmetry axis. The electron density maps clearly show the relative orientation of the subunits and most of the trace of the polypeptide chain. Each subunit consists of two domains. The topology of the large domain appears to be similar to that of the aminotransferases.
    Full-text · Article · Jun 1992 · FEBS Letters
  • No preview · Chapter · Dec 1991
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    [Show abstract] [Hide abstract] ABSTRACT: Single crystals of D-serine dehydratase from Escherichia coli complexed with 3-amino-2-hydroxypropionate have been obtained from ammonium sulfate solution (pH 7.0) by vapor diffusion. The crystals belong to the trigonal space group P3(1) or P3(2) with a = b = 81.3 A and c = 58.4 A. The asymmetric unit cell contains one protein molecule with Mr = 48,289. The crystals diffract to at least 3.0 A resolution and are suitable for X-ray structure analysis.
    Full-text · Article · Sep 1990 · Journal of Molecular Biology

Publication Stats

979 Citations
76.16 Total Impact Points


  • 1997
    • Lomonosov Moscow State University
      Moskva, Moscow, Russia
  • 1989-1997
    • Russian Academy of Sciences
      • Institute of Crystallography
      Moskva, Moscow, Russia
  • 1994
    • Deutsches Elektronen-Synchrotron
      Hamburg, Hamburg, Germany