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Alpha-Amino Acid

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Thomas R M Barends – One of the best experts on this subject based on the ideXlab platform.

  • Acetobacter turbidans Alpha-Amino Acid ester hydrolase: merohedral twinning in P21 obscured by pseudo-translational NCS.
    Acta crystallographica. Section D Biological crystallography, 2003
    Co-Authors: Thomas R M Barends, Bauke W. Dijkstra

    Abstract:

    The structure elucidation of the Alpha-Amino Acid ester hydrolase from Acetobacter turbidans by molecular replacement is described. In the monoclinic crystal, the molecules are related by both rotational and pseudo-crystallographic translational NCS (non-crystallographic symmetry). Refinement of the structure converged at unacceptably high R factors. After re-evaluation of the data, it was found that the crystal was merohedrally twinned, with a high twinning fraction. It is shown that the pseudo-crystallographic NCS causes aberrant behaviour of conventional twinning indicators, which explains why the twinning was only realized at the refinement stage.

  • Acetobacter turbidans Alpha-Amino Acid ester hydrolase
    Acta Crystallographica Section D Biological Crystallography, 2003
    Co-Authors: Thomas R M Barends, Bauke W. Dijkstra

    Abstract:

    The structure elucidation of the Alpha-Amino Acid ester hydrolase from Acetobacter turbidans by molecular replacement is described. In the monoclinic crystal, the molecules are related by both rotational and pseudo-crystallographic translational NCS (non-crystallographic symmetry). Refinement of the structure converged at unacceptably high R factors. After re-evaluation of the data, it was found that the crystal was merohedrally twinned, with a high twinning fraction. It is shown that the pseudo-crystallographic NCS causes aberrant behaviour of conventional twinning indicators, which explains why the twinning was only realized at the refinement stage.

  • the sequence and crystal structure of the alpha amino Acid ester hydrolase from xanthomonas citri define a new family of beta lactam antibiotic acylases
    Journal of Biological Chemistry, 2003
    Co-Authors: Thomas R M Barends, Jolanda Polderman Tijmes, Peter A Jekel, Cmh Hensgens, Erik De Vries, Dick B. Janssen, Bebauke W Dijkstra

    Abstract:

    Abstract α-Amino Acid ester hydrolases (AEHs) catalyze the hydrolysis and synthesis of esters and amides with an α-amino group. As such, they can synthesize β-lactam antibiotics from acyl compounds and β-lactam nuclei obtained from the hydrolysis of natural antibiotics. This article describes the gene sequence and the 1.9-A resolution crystal structure of the AEH from Xanthomonas citri. The enzyme consists of an α/β-hydrolase fold domain, a helical cap domain, and a jellyroll β-domain. Structural homology was observed to the Rhodococcus cocaine esterase, indicating that both enzymes belong to the same class of bacterial hydrolases. Docking of a β-lactam antibiotic in the active site explains the substrate specificity, specifically the necessity of an α-amino group on the substrate, and explains the low specificity toward the β-lactam nucleus.

Leslie Leiserowitz – One of the best experts on this subject based on the ideXlab platform.

  • separation of enantiomers and racemate formation in two dimensional crystals at the water surface from racemic alpha amino Acid amphiphiles design and structure
    Journal of the American Chemical Society, 1997
    Co-Authors: Isabelle Weissbuch, Maria Berfeld, Wim G Bouwman, Kristian Kjaer, J Alsnielsen, Meir Lahav, Leslie Leiserowitz

    Abstract:

    Studies are presented on the two-dimensional (2-D) crystalline packing arrangements of enantiomerically pure and racemic α-amino Acid RHC(NH3+)CO2- monolayers on water and on glycine aqueous solutions, as determined by synchrotron grazing incidence X-ray diffraction. The amphiphiles have been designed such that their racemic mixtures form 2-D crystals which are either heterochiral (for R = CnH2n+1−, n = 10, 12, 16) due to the tendency for herringbone chain arrangements via glide symmetry or homochiral (for R = CnH2n+1CONH(CH2)4−, n = 11, 17, 21) by virtue of hydrogen bonding by translation of the amide group in the chains leading to a spontaneous separation into islands of opposite chirality. The two different crystalline motifs led to a correlation between their packing arrangements and induced oriented nucleation of 3-D crystals of α-glycine by these monolayers. The relevance of the present results to the possibility of ordering and spontaneous segregation of racemates of the natural hydrophobic α-amino…

  • The role of crystal polarity in Alpha-Amino Acid crystals for induced nucleation of ice
    Science (New York N.Y.), 1992
    Co-Authors: Moshe Gavish, J. L. Wang, M Eisenstein, Michal Lahav, Leslie Leiserowitz

    Abstract:

    The hydrophobic faces of single crystals of a series of pairs of racemic and chiral-resolved hydrophobic Alpha-Amino Acids were used as a substrate, onto which water vapor has been cooled to freezing. The morphologies and molecular packing arrangements within each crystal pair are similar but only one of each pair exhibits a polar axis, parallel to the hydrophobic face exposed to water. Those crystals that have a polar axis induce a freezing point higher by 4 degrees to 5 degrees C than the corresponding crystals that do not have a polar axis. The results are interpreted in terms of an electric field mechanism that helps align the water molecules into ice-like clusters en route to crystallization.

Bauke W. Dijkstra – One of the best experts on this subject based on the ideXlab platform.

  • Acetobacter turbidans Alpha-Amino Acid ester hydrolase
    Acta Crystallographica Section D Biological Crystallography, 2003
    Co-Authors: Thomas R M Barends, Bauke W. Dijkstra

    Abstract:

    The structure elucidation of the Alpha-Amino Acid ester hydrolase from Acetobacter turbidans by molecular replacement is described. In the monoclinic crystal, the molecules are related by both rotational and pseudo-crystallographic translational NCS (non-crystallographic symmetry). Refinement of the structure converged at unacceptably high R factors. After re-evaluation of the data, it was found that the crystal was merohedrally twinned, with a high twinning fraction. It is shown that the pseudo-crystallographic NCS causes aberrant behaviour of conventional twinning indicators, which explains why the twinning was only realized at the refinement stage.

  • Acetobacter turbidans Alpha-Amino Acid ester hydrolase: merohedral twinning in P21 obscured by pseudo-translational NCS.
    Acta crystallographica. Section D Biological crystallography, 2003
    Co-Authors: Thomas R M Barends, Bauke W. Dijkstra

    Abstract:

    The structure elucidation of the Alpha-Amino Acid ester hydrolase from Acetobacter turbidans by molecular replacement is described. In the monoclinic crystal, the molecules are related by both rotational and pseudo-crystallographic translational NCS (non-crystallographic symmetry). Refinement of the structure converged at unacceptably high R factors. After re-evaluation of the data, it was found that the crystal was merohedrally twinned, with a high twinning fraction. It is shown that the pseudo-crystallographic NCS causes aberrant behaviour of conventional twinning indicators, which explains why the twinning was only realized at the refinement stage.