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See detailCoordination sphere of the third metal site is essential to the activity and metal selectivity of alkaline phosphatases
Koutsioulis, D.; Lyskowski, A.; Maki, S. et al

in Protein Science : A Publication of the Protein Society (2010), 19(1), 75-84

Alkaline phosphatases (APs) are commercially applied enzymes that catalyze the hydrolysis of phosphate monoesters by a reaction involving three active site metal ions. We have previously identified H135 ... [more ▼]

Alkaline phosphatases (APs) are commercially applied enzymes that catalyze the hydrolysis of phosphate monoesters by a reaction involving three active site metal ions. We have previously identified H135 as the key residue for controlling activity of the psychrophilic TAB5 AP (TAP). In this article, we describe three X-ray crystallographic structures on TAP variants H135E and H135D in complex with a variety of metal ions. The structural analysis is supported by thermodynamic and kinetic data. The AP catalysis essentially requires octahedral coordination in the M3 site, but stability is adjusted with the conformational freedom of the metal ion. Comparison with the mesophilic Escherichia coli, AP shows differences in the charge transfer network in providing the chemically optimal metal combination for catalysis. Our results provide explanation why the TAB5 and E. coli APs respond in an opposite way to mutagenesis in their active sites. They provide a lesson on chemical fine tuning and the importance of the second coordination sphere in defining metal specificity in enzymes. Understanding the framework of AP catalysis is essential in the efforts to design even more powerful tools for modern biotechnology. [less ▲]

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See detailBiophysical studies support a predicted superhelical structure with armadillo repeats for Ric-8.
Figueroa, Maximiliano ULg; Hinrichs, Maria Victoria; Bunster, Marta et al

in Protein Science : A Publication of the Protein Society (2009), 18(6), 1139-45

Ric-8 is a highly conserved cytosolic protein (MW 63 KDa) initially identified in C. elegans as an essential factor in neurotransmitter release and asymmetric cell division. Two different isoforms have ... [more ▼]

Ric-8 is a highly conserved cytosolic protein (MW 63 KDa) initially identified in C. elegans as an essential factor in neurotransmitter release and asymmetric cell division. Two different isoforms have been described in mammals, Ric-8A and Ric-8B; each possess guanine nucleotide exchange activity (GEF) on heterotrimeric G-proteins, but with different Galpha subunits specificities. To gain insight on the mechanisms involved in Ric-8 cellular functions it is essential to obtain some information about its structure. Therefore, the aim of this work was to create a structural model for Ric-8. In this case, it was not possible to construct a model based on comparison with a template structure because Ric-8 does not present sequence similarity with any other protein. Consequently, different bioinformatics approaches that include protein folding and structure prediction were used. The Ric-8 structural model is composed of 10 armadillo folding motifs, organized in a right-twisted alpha-alpha super helix. In order to validate the structural model, a His-tag fusion construct of Ric-8 was expressed in E. coli, purified by affinity and anion exchange chromatography and subjected to circular dichroism analysis (CD) and thermostability studies. Ric-8 is approximately 80% alpha helix, with a Tm of 43.1 degrees C, consistent with an armadillo-type structure such as alpha-importin, a protein composed of 10 armadillo repeats. The proposed structural model for Ric-8 is intriguing because armadillo proteins are known to interact with multiple partners and participate in diverse cellular functions. These results open the possibility of finding new protein partners for Ric-8 with new cellular functions. [less ▲]

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See detailInteractions of apomyoglobin with membranes: Mechanisms and effects on heme uptake
Vernier, Gregory; Chenal, Alexandre; Vitrac, Heidi et al

in Protein Science : A Publication of the Protein Society (2007)

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See detailThe Bacillus licheniformis BlaP beta-lactamase as a model protein scaffold to study the insertion of protein fragments.
Vandevenne, Marylène ULg; Filée, Patrice ULg; Scarafone, Natacha ULg et al

in Protein Science : A Publication of the Protein Society (2007), 16(10), 2260-71

Using genetic engineering technologies, the chitin-binding domain (ChBD) of the human macrophage chitotriosidase has been inserted into the host protein BlaP, a class A beta-lactamase produced by Bacillus ... [more ▼]

Using genetic engineering technologies, the chitin-binding domain (ChBD) of the human macrophage chitotriosidase has been inserted into the host protein BlaP, a class A beta-lactamase produced by Bacillus licheniformis. The product of this construction behaved as a soluble chimeric protein that conserves both the capacity to bind chitin and to hydrolyze beta-lactam moiety. Here we describe the biochemical and biophysical properties of this protein (BlaPChBD). This work contributes to a better understanding of the reciprocal structural and functional effects of the insertion on the host protein scaffold and the heterologous structured protein fragments. The use of BlaP as a protein carrier represents an efficient approach to the functional study of heterologous protein fragments. [less ▲]

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See detailImproving the alkalophilic performances of the Xyl1 xylanase from Streptomyces sp S38: Structural comparison and mutational analysis
De Lemos Esteves, Frédéric ULg; Gouders, T.; Lamotte-Brasseur, J. et al

in Protein Science : A Publication of the Protein Society (2005), 14(2), 292-302

Endo-beta-1,4-xylanases of the family 11 glycosyl-hydrolases are catalytically active over a wide range of pH. Xyl1 from Streptomyces sp. S38 belongs to this family, and its optimum pH for enzymatic ... [more ▼]

Endo-beta-1,4-xylanases of the family 11 glycosyl-hydrolases are catalytically active over a wide range of pH. Xyl1 from Streptomyces sp. S38 belongs to this family, and its optimum pH for enzymatic activity is 6. Xyn11 from Bacillus agaradhaerens and XylJ from Bacillus sp. 41M-1 share 85% sequence identity and have been described as highly alkalophilic enzymes. In an attempt to better understand the alkalophilic adaptation of xylanases, the three-dimensional structures of Xyn11 and Xyl1 were compared. This comparison highlighted an increased number of salt-bridges and the presence of more charged residues in the catalytic cleft as well as an eight-residue-longer loop in the alkalophilic xylanase Xyn11. Some of these charges were introduced in the structure of Xyl1 by site-directed mutagenesis with substitutions Y16D, S18E, G50R, N92D, A135Q, E139K, and Y186E. Furthermore, the eight additional loop residues of Xyn11 were introduced in the homologous loop of Xyl1. In addition, the coding sequence of the XylJ catalytic domain was synthesized by recursive PCR, expressed in a Streptomyces host, purified, and characterized together with the Xyl1 mutants. The Y186E substitution inactivated Xyl1, but the activity was restored when this mutation was combined with the G50R or S18E substitutions. Interestingly, the E139K mutation raised the optimum pH of Xyl1 from 6 to 7.5 but had no effect when combined with the N92D substitution. Modeling studies identified the possible formation of an interaction between the introduced lysine and the substrate, which could be eliminated by the formation of a putative salt-bridge in the N92D/E139K mutant. [less ▲]

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See detailFusogenic Alzheimer'S Peptide Fragment A Beta (29-42) In Interaction With Lipid Bilayers: Secondary Structure, Dynamics, And Specific Interaction With Phosphatidyl Ethanolamine Polar Heads As Revealed By Solid-State Nmr
Ravault, S.; Soubias, O.; Saurel, O. et al

in Protein Science : A Publication of the Protein Society (2005), 14(5), 1181-9

The interaction of the native Alzheimer's peptide C-terminal fragment Abeta (29-42), and two mutants (G33A and G37A) with neutral lipid bilayers made of POPC and POPE in a 9:1 molar ratio was investigated ... [more ▼]

The interaction of the native Alzheimer's peptide C-terminal fragment Abeta (29-42), and two mutants (G33A and G37A) with neutral lipid bilayers made of POPC and POPE in a 9:1 molar ratio was investigated by solid-state NMR. This fragment and the lipid composition were selected because they represent the minimum requirement for the fusogenic activity of the Alzheimer's peptide. The chemical shifts of alanine methyl isotropic carbon were determined by MAS NMR, and they clearly demonstrated that the major form of the peptide equilibrated in membrane is not in a helical conformation. (2)H NMR, performed with acyl chain deuterated POPC, demonstrated that there is no perturbation of the acyl chain's dynamics and of the lipid phase transition temperature. (2)H NMR, performed with alanine methyl-deuterated peptide demonstrated that the peptide itself has a limited mobility below and above the lipid phase transition temperature (molecular order parameter equal to 0.94). MAS (31)P NMR revealed a specific interaction with POPE polar head as seen by the enhancement of POPE phosphorus nuclei T(2) relaxation. All these results are in favor of a beta-sheet oligomeric association of the peptide at the bilayer interface, preferentially recruiting phosphatidyl ethanolamine polar heads. [less ▲]

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See detailCrystal structures of oxidized and reduced forms of human mitochondrial thioredoxin 2
Smeets, Aude; Evrard, Christine ULg; Landtmeters, Marie et al

in Protein Science : A Publication of the Protein Society (2005), 14

Mammalian thioredoxin 2 is a mitochondrial isoform of highly evolutionary conserved thioredoxins. Thioredoxins are small ubiquitous protein–disulfide oxidoreductases implicated in a large variety of ... [more ▼]

Mammalian thioredoxin 2 is a mitochondrial isoform of highly evolutionary conserved thioredoxins. Thioredoxins are small ubiquitous protein–disulfide oxidoreductases implicated in a large variety of biological functions. In mammals, thioredoxin 2 is encoded by a nuclear gene and is targeted to mitochondria by a N-terminal mitochondrial presequence. Recently, mitochondrial thioredoxin 2 was shown to interact with components of the mitochondrial respiratory chain and to play a role in the control of mitochondrial membrane potential, regulating mitochondrial apoptosis signaling pathway. Here we report the first crystal structures of a mammalian mitochondrial thioredoxin 2. Crystal forms of reduced and oxidized human thioredoxin 2 are described at 2.0 and 1.8A ˚ resolution. Though the folding is rather similar to that of human cytosolic/nuclear thioredoxin 1, important differences are observed during the transition between the oxidized and the reduced states of human thioredoxin 2, compared with human thioredoxin 1. In spite of the absence of the Cys residue implicated in dimer formation in human thioredoxin 1, dimerization still occurs in the crystal structure of human thioredoxin 2, mainly mediated by hydrophobic contacts, and the dimers are associated to form two-dimensional polymers. Interestingly, the structure of human thioredoxin 2 reveals possible interaction domains with human peroxiredoxin 5, a substrate protein of human thioredoxin 2 in mitochondria. [less ▲]

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See detailSpecificity inversion of Ochrobactrum anthropi D-aminopeptidase to a D,D-carboxypeptidase with new penicillin binding activity by directed mutagenesis
Delmarcelle, Michaël ULg; Boursoit, Marie-Caroline; Filée, Patrice ULg et al

in Protein Science : A Publication of the Protein Society (2005), 14

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See detailAcidophilic adaptation of family 11 endo--1,4-xylanases: Modeling and mutational analysis
De Lemos Esteves, Frédéric ULg; Ruelle, Virginie; Lamotte-Brasseur, Josette ULg et al

in Protein Science : A Publication of the Protein Society (2004), 13(5), 12091218

Xyl1 from Streptomyces sp. S38 belongs to the low molecular mass family 11 of endo--1,4-xylanases. Its three-dimensional structure has been solved at 2.0 Å and its optimum temperature and pH for enzymatic ... [more ▼]

Xyl1 from Streptomyces sp. S38 belongs to the low molecular mass family 11 of endo--1,4-xylanases. Its three-dimensional structure has been solved at 2.0 Å and its optimum temperature and pH for enzymatic activity are 60°C and 6.0, respectively. Aspergillus kawachii xylanase XynC belongs to the same family but is an acidophilic enzyme with an optimum pH of 2.0. Structural comparison of Xyl1 and XynC showed differences in residues surrounding the two glutamic acid side chains involved in the catalysis that could be responsible for the acidophilic adaptation of XynC. Mutations W20Y, N48D, A134E, and Y193W were introduced by site-directed mutagenesis and combined in multiple mutants. Trp 20 and Tyr 193 are involved in substrate binding. The Y193W mutation inactivated Xyl1 whereas W20Y decreased the optimum pH of Xyl1 to 5.0 and slightly increased its specific activity. The N48D mutation also decreased the optimum pH of Xyl1 by one unit. The A134E substitution did not induce any change, but when combined with N48D, a synergistic effect was observed with a 1.4 unit decrease in the optimum pH. Modeling showed that the orientations of residue 193 and of the fully conserved Arg 131 are different in acidophilic and alkaline xylanases whereas the introduced Tyr 20 probably modifies the pKa of the acid-base catalyst via residue Asn 48. Docking of a substrate analog in the catalytic site highlighted striking differences between Xyl1 and XynC in substrate binding. Hydrophobicity calculations showed a correlation between acidophilic adaptation and a decreased hydrophobicity around the two glutamic acid side chains involved in catalysis. [less ▲]

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See detailRevisiting The Ramachandran Plot: Hard-Sphere Repulsion, Electrostatics, And H-Bonding In The Alpha-Helix
Ho, Bk.; Thomas, Annick ULg; Brasseur, Robert ULg

in Protein Science : A Publication of the Protein Society (2003), 12(11), 2508-22

What determines the shape of the allowed regions in the Ramachandran plot? Although Ramachandran explained these regions in terms of 1-4 hard-sphere repulsions, there are discrepancies with the data where ... [more ▼]

What determines the shape of the allowed regions in the Ramachandran plot? Although Ramachandran explained these regions in terms of 1-4 hard-sphere repulsions, there are discrepancies with the data where, in particular, the alphaR, alphaL, and beta-strand regions are diagonal. The alphaR-region also varies along the alpha-helix where it is constrained at the center and the amino terminus but diffuse at the carboxyl terminus. By analyzing a high-resolution database of protein structures, we find that certain 1-4 hard-sphere repulsions in the standard steric map of Ramachandran do not affect the statistical distributions. By ignoring these steric clashes (NH(i+1) and O(i-1)C), we identify a revised set of steric clashes (CbetaO, O(i-1)N(i+1), CbetaN(i+1), O(i-1)Cbeta, and O(i-1)O) that produce a better match with the data. We also find that the strictly forbidden region in the Ramachandran plot is excluded by multiple steric clashes, whereas the outlier region is excluded by only one significant steric clash. However, steric clashes alone do not account for the diagonal regions. Using electrostatics to analyze the conformational dependence of specific interatomic interactions, we find that the diagonal shape of the alphaR and alphaL-regions also depends on the optimization of the NH(i+1) and O(i-1)C interactions, and the diagonal beta-strand region is due to the alignment of the CO and NH dipoles. Finally, we reproduce the variation of the Ramachandran plot along the alpha-helix in a simple model that uses only H-bonding constraints. This allows us to rationalize the difference between the amino terminus and the carboxyl terminus of the alpha-helix in terms of backbone entropy. [less ▲]

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See detailAnalysis Of Accessible Surface Of Residues In Proteins
Lins, Laurence ULg; Thomas, Annick ULg; Brasseur, Robert ULg

in Protein Science : A Publication of the Protein Society (2003), 12(7),

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See detailStructural basis of alpha-amylase activation by chloride
Aghajari, N.; Feller, Georges ULg; Gerday, Charles ULg et al

in Protein Science : A Publication of the Protein Society (2002), 11(6), 1435-1441

To further investigate the mechanism and function of allosteric activation by chloride in some alpha-amylases, the structure of the bacterial alpha-amylase from the psychrophilic micro-organism ... [more ▼]

To further investigate the mechanism and function of allosteric activation by chloride in some alpha-amylases, the structure of the bacterial alpha-amylase from the psychrophilic micro-organism Pseudoalteromonas haloplanktis in complex with nitrate has been solved at 2.1 Angstrom, as well as the structure of the mutants Lys300Gln (2.5 Angstrom) and Lys300Arg (2.25 Angstrom). Nitrate binds strongly to alpha-amylase but is a weak activator. Mutation of the critical chloride ligand Lys300 into Gln results in a chloride-independent enzyme, whereas the mutation into Arg mimics the binding site as is found in animal alpha-amylases with, however, a lower affinity for chloride. These structures reveal that the triangular conformation of the chloride ligands and the nearly equatorial coordination allow the perfect accommodation of planar trigonal monovalent anions such as NO3-, explaining their unusual strong binding. It is also shown that a localized negative charge such as that of Cl-, rather than a delocalized charge as in the case of nitrate, is essential for maximal activation. The chloride-free mutant Lys300Gln indicates that chloride is not mandatory for the catalytic mechanism but strongly increases the reactivity at the active site. Disappearance of the putative catalytic water molecule in this weakly active mutant supports the view that chloride helps to polarize the hydrolytic water molecule and enhances the rate of the second step in the catalytic reaction. [less ▲]

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See detailSingle-domain antibody fragments with high conformational stability.
Dumoulin, Mireille ULg; Conrath, Katja; Van Meirhaeghe, Annemie et al

in Protein Science : A Publication of the Protein Society (2002), 11(3), 500-15

A variety of techniques, including high-pressure unfolding monitored by Fourier transform infrared spectroscopy, fluorescence, circular dichroism, and surface plasmon resonance spectroscopy, have been ... [more ▼]

A variety of techniques, including high-pressure unfolding monitored by Fourier transform infrared spectroscopy, fluorescence, circular dichroism, and surface plasmon resonance spectroscopy, have been used to investigate the equilibrium folding properties of six single-domain antigen binders derived from camelid heavy-chain antibodies with specificities for lysozymes, beta-lactamases, and a dye (RR6). Various denaturing conditions (guanidinium chloride, urea, temperature, and pressure) provided complementary and independent methods for characterizing the stability and unfolding properties of the antibody fragments. With all binders, complete recovery of the biological activity after renaturation demonstrates that chemical-induced unfolding is fully reversible. Furthermore, denaturation experiments followed by optical spectroscopic methods and affinity measurements indicate that the antibody fragments are unfolded cooperatively in a single transition. Thus, unfolding/refolding equilibrium proceeds via a simple two-state mechanism (N <--> U), where only the native and the denatured states are significantly populated. Thermally-induced denaturation, however, is not completely reversible, and the partial loss of binding capacity might be due, at least in part, to incorrect refolding of the long loops (CDRs), which are responsible for antigen recognition. Most interestingly, all the fragments are rather resistant to heat-induced denaturation (apparent T(m) = 60-80 degrees C), and display high conformational stabilities (DeltaG(H(2)O) = 30-60 kJ mole(-1)). Such high thermodynamic stability has never been reported for any functional conventional antibody fragment, even when engineered antigen binders are considered. Hence, the reduced size, improved solubility, and higher stability of the camelid heavy-chain antibody fragments are of special interest for biotechnological and medical applications. [less ▲]

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See detailAn Additional Aromatic Interaction Improves the Thermostability and Thermophilicity of a Mesophilic Family 11 Xylanase: Structural Basis and Molecular Study
Georis, J.; De Lemos Esteves, Frédéric ULg; Lamotte-Brasseur, J. et al

in Protein Science : A Publication of the Protein Society (2000), 9(3), 466-75

In a general approach to the understanding of protein adaptation to high temperature, molecular models of the closely related mesophilic Streptomyces sp. S38 Xyl1 and thermophilic Thermomonospora fusca ... [more ▼]

In a general approach to the understanding of protein adaptation to high temperature, molecular models of the closely related mesophilic Streptomyces sp. S38 Xyl1 and thermophilic Thermomonospora fusca TfxA family 11 xylanases were built and compared with the three-dimensional (3D) structures of homologous enzymes. Some of the structural features identified as potential contributors to the higher thermostability of TfxA were introduced in Xyl1 by site-directed mutagenesis in an attempt to improve its thermostability and thermophilicity. A new Y11-Y16 aromatic interaction, similar to that present in TfxA and created in Xyl1 by the T11Y mutation, improved both the thermophilicity and thermostability. Indeed, the optimum activity temperature (70 vs. 60 degrees C) and the apparent Tm were increased by about 9 degrees C, and the mutant was sixfold more stable at 57 degrees C. The combined mutations A82R/F168H/N169D/delta170 potentially creating a R82-D169 salt bridge homologous to that present in TfxA improved the thermostability but not the thermophilicity. Mutations R82/D170 and S33P seemed to be slightly destabilizing and devoid of influence on the optimal activity temperature of Xyl1. Structural analysis revealed that residues Y11 and Y16 were located on beta-strands B1 and B2, respectively. This interaction should increase the stability of the N-terminal part of Xyl1. Moreover, Y11 and Y16 seem to form an aromatic continuum with five other residues forming putative subsites involved in the binding of xylan (+3, +2, +1, -1, -2). Y11 and Y16 might represent two additional binding subsites (-3, -4) and the T11Y mutation could thus improve substrate binding to the enzyme at higher temperature and thus the thermophilicity of Xyl1. [less ▲]

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See detailCrystal structure of the EF-hand parvalbumin at atomic resolution (0.91 Å) and at low temperature (100 K). Evidence for conformational multistates within the hydrophobic core.
Declercq, Jean-Paul; Evrard, Christine ULg; Lamzin, Victor et al

in Protein Science : A Publication of the Protein Society (1999), 8

Several crystal structures of parvalbumin (Parv), a typical EF-hand protein, have been reported so far for different species with the best resolution achieving 1.5 Å. Using a crystal grown under ... [more ▼]

Several crystal structures of parvalbumin (Parv), a typical EF-hand protein, have been reported so far for different species with the best resolution achieving 1.5 Å. Using a crystal grown under microgravity conditions, cryotechniques (100 K), and synchrotron radiation, it has now been possible to determine the crystal structure of the fully Ca2+ loaded form of pike (component pI 4.10) Parv.Ca2 at atomic resolution (0.91 Å). The availability of such a high quality structure offers the opportunity to contribute to the definition of the validation tools useful for the refinement of protein crystal structures determined to lower resolution. Besides a better definition of most of the elements in the protein threedimensional structure than in previous studies, the high accuracy thus achieved allows the detection of well-defined alternate conformations, which are observed for 16 residues out of 107 in total. Among them, six occupy an internal position within the hydrophobic core and converge toward two small buried cavities with a total volume of about 60 Å3. There is no indication of any water molecule present in these cavities. It is probable that at temperatures of physiological conditions there is a dynamic interconversion between these alternate conformations in an energy-barrier dependent manner. Such motions for which the amplitudes are provided by the present study will be associated with a timedependent remodeling of the void internal space as part of a slow dynamics regime (millisecond timescales) of the parvalbumin molecule. The relevance of such internal dynamics to function is discussed. [less ▲]

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See detailCrystal structures of the psychrophilic a-amylase from Alteromonas haloplanctis in its native form and complexed with an inhibitor
Aghajari, N.; Feller, Georges ULg; Gerday, Charles ULg et al

in Protein Science : A Publication of the Protein Society (1998), 7(6), 564-572

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See detailCrystallization and preliminary X-ray diffraction studies of a-amylase from the antarctic psychrophile Alteromonas haloplanctis A23
Aghajari, N.; Feller, Georges ULg; Gerday, Charles ULg et al

in Protein Science : A Publication of the Protein Society (1996), 5(10), 2128-2129

A cold-active alpha-amylase was purified from culture supernatants of the antarctic psychrophile Alteromonas haloplanctis A23 grown at 4 degrees C. In order to contribute to the understanding of the ... [more ▼]

A cold-active alpha-amylase was purified from culture supernatants of the antarctic psychrophile Alteromonas haloplanctis A23 grown at 4 degrees C. In order to contribute to the understanding of the molecular basis of cold adaptations, crystallographic studies of this cold-adapted enzyme have been initiated because a three-dimensional structure of a mesophilic counterpart, pig pancreatic alpha-amylase, already exists. alpha-Amylase from A. haloplanctis, which shares 53% sequence identity with pig pancreatic alpha-amylase, has been crystallized and data to 1.85 A have been collected. The space group is found to be C222(1) with a = 71.40 A, b = 138.88 A, and c = 115.66 A. Until now, a three-dimensional structure of a psychrophilic enzyme is lacking. [less ▲]

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See detailCrystal structure of recombinant triosephosphate isomerase from Bacillus stearothermophilus. An analysis of potential thermostability factors in six isomerases with known three-dimensional structures points to the importance of hydrophobic interactions
Delboni, Luis F; Mande, Shekhar C; Rentier-Delrue, Françoise ULg et al

in Protein Science : A Publication of the Protein Society (1995), 4(12), 2594-604

The structure of the thermostable triosephosphate isomerase (TIM) from Bacillus stearothermophilus complexed with the competitive inhibitor 2-phosphoglycolate was determined by X-ray crystallography to a ... [more ▼]

The structure of the thermostable triosephosphate isomerase (TIM) from Bacillus stearothermophilus complexed with the competitive inhibitor 2-phosphoglycolate was determined by X-ray crystallography to a resolution of 2.8 A. The structure was solved by molecular replacement using XPLOR. Twofold averaging and solvent flattening was applied to improve the quality of the map. Active sites in both the subunits are occupied by the inhibitor and the flexible loop adopts the "closed" conformation in either subunit. The crystallographic R-factor is 17.6% with good geometry. The two subunits have an RMS deviation of 0.29 A for 248 C alpha atoms and have average temperature factors of 18.9 and 15.9 A2, respectively. In both subunits, the active site Lys 10 adopts an unusual phi, psi combination. A comparison between the six known thermophilic and mesophilic TIM structures was conducted in order to understand the higher stability of B. stearothermophilus TIM. Although the ratio Arg/(Arg+Lys) is higher in B. stearothermophilus TIM, the structure comparisons do not directly correlate this higher ratio to the better stability of the B. stearothermophilus enzyme. A higher number of prolines contributes to the higher stability of B. stearothermophilus TIM. Analysis of the known TIM sequences points out that the replacement of a structurally crucial asparagine by a histidine at the interface of monomers, thus avoiding the risk of deamidation and thereby introducing a negative charge at the interface, may be one of the factors for adaptability at higher temperatures in the TIM family. Analysis of buried cavities and the areas lining these cavities also contributes to the greater thermal stability of the B. stearothermophilus enzyme. However, the most outstanding result of the structure comparisons appears to point to the hydrophobic stabilization of dimer formation by burying the largest amount of hydrophobic surface area in B. stearothermophilus TIM compared to all five other known TIM structures. [less ▲]

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See detailCrystal structure of recombinant human triosephosphate isomerase at 2.8 A resolution. Triosephosphate isomerase-related human genetic disorders and comparison with the trypanosomal enzyme
Mande, S. C.; Mainfroid, V.; Kalk, K. H. et al

in Protein Science : A Publication of the Protein Society (1994), 3(5), 810-21

The crystal structure of recombinant human triosephosphate isomerase (hTIM) has been determined complexed with the transition-state analogue 2-phosphoglycolate at a resolution of 2.8 A. After refinement ... [more ▼]

The crystal structure of recombinant human triosephosphate isomerase (hTIM) has been determined complexed with the transition-state analogue 2-phosphoglycolate at a resolution of 2.8 A. After refinement, the R-factor is 16.7% with good geometry. The asymmetric unit contains 1 complete dimer of 53,000 Da, with only 1 of the subunits binding the inhibitor. The so-called flexible loop, comprising residues 168-174, is in its "closed" conformation in the subunit that binds the inhibitor, and in the "open" conformation in the other subunit. The tips of the loop in these 2 conformations differ up to 7 A in position. The RMS difference between hTIM and the enzyme of Trypanosoma brucei, the causative agent of sleeping sickness, is 1.12 A for 487 C alpha positions with 53% sequence identity. Significant sequence differences between the human and parasite enzymes occur at about 13 A from the phosphate binding site. The chicken and human enzymes have an RMS difference of 0.69 A for 484 equivalent residues and about 90% sequence identity. Complementary mutations ensure a great similarity in the packing of side chains in the core of the beta-barrels of these 2 enzymes. Three point mutations in hTIM have been correlated with severe genetic disorders ranging from hemolytic disorder to neuromuscular impairment. Knowledge of the structure of the human enzyme provides insight into the probable effect of 2 of these mutations, Glu 104 to Asp and Phe 240 to Ile, on the enzyme. The third mutation reported to be responsible for a genetic disorder, Gly 122 to Arg, is however difficult to explain. This residue is far away from both catalytic centers in the dimer, as well as from the dimer interface, and seems unlikely to affect stability or activity. Inspection of the 3-dimensional structure of trypanosomal triosephosphate isomerase, which has a methionine at position 122, only increased the mystery of the effects of the Gly to Arg mutation in the human enzyme. [less ▲]

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See detailCrystal structure of cholera toxin B-pentamer bound to receptor GM1 pentasaccharide
Merritt, E. A.; Sarfaty, S.; van den Akker, F. et al

in Protein Science : A Publication of the Protein Society (1994), 3(2), 166-75

Cholera toxin (CT) is an AB5 hexameric protein responsible for the symptoms produced by Vibrio cholerae infection. In the first step of cell intoxication, the B-pentamer of the toxin binds specifically to ... [more ▼]

Cholera toxin (CT) is an AB5 hexameric protein responsible for the symptoms produced by Vibrio cholerae infection. In the first step of cell intoxication, the B-pentamer of the toxin binds specifically to the branched pentasaccharide moiety of ganglioside GM1 on the surface of target human intestinal epithelial cells. We present here the crystal structure of the cholera toxin B-pentamer complexed with the GM1 pentasaccharide. Each receptor binding site on the toxin is found to lie primarily within a single B-subunit, with a single solvent-mediated hydrogen bond from residue Gly 33 of an adjacent subunit. The large majority of interactions between the receptor and the toxin involve the 2 terminal sugars of GM1, galactose and sialic acid, with a smaller contribution from the N-acetyl galactosamine residue. The binding of GM1 to cholera toxin thus resembles a 2-fingered grip: the Gal(beta 1-3)GalNAc moiety representing the "forefinger" and the sialic acid representing the "thumb." The residues forming the binding site are conserved between cholera toxin and the homologous heat-labile enterotoxin from Escherichia coli, with the sole exception of His 13. Some reported differences in the binding affinity of the 2 toxins for gangliosides other than GM1 may be rationalized by sequence differences at this residue. The CTB5:GM1 pentasaccharide complex described here provides a detailed view of a protein:ganglioside specific binding interaction, and as such is of interest not only for understanding cholera pathogenesis and for the design of drugs and development of vaccines but also for modeling other protein:ganglioside interactions such as those involved in GM1-mediated signal transduction. [less ▲]

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