Carbohydrate crystallography

The earlier article on the crystallography of carbohydrates described its infancy, and the present one covers its adolescence. The lack of maturity is attributable to the scarcity of interdisciplinary studies and correlations. The coming of age of carbohydrate crystallography will occur when widespread use is made of conformational studies, reaction mechanisms, and the charge distribution, the geometry and the electron density being determined crystallo-graphically. 

In spite of their easy interconversion in solution a and p forms of carbohydrates are capable of independent existence and many have been isolated m pure form as crys talline solids When crystallized from ethanol d glucose yields a d glucopyranose mp 146°C [a]o +112 2° Crystallization from a water-ethanol mixture produces p d glucopyranose mp 148-155°C [aj +18 7° In the solid state the two forms do not mterconvert and are stable indefinitely Their structures have been unambiguously con firmed by X ray crystallography... 

Wardell et al. studied the preparation, reactivities, and structures of C(carbohydrate)-Sn bonded mono-, or di-O-isopropylidene or di-O-benzylidene triphenylstannyl-carbohydrate derivatives by means of X-ray crystallography. 

The reaction mechanism of a-amylases is referred to as retaining, which means that the stereochemistry at the cleaved bond of the carbohydrate is retained. Hydrolysis of the glycosidic bond is mediated by an acid hydrolysis mechanism, which is in turn mediated by Aspl97 and Glu233 in pig pancreatic amylase. These interactions have been identified from X-ray crystallography. The aspartate residue has been shown to form a covalent bond with the Cl position of the substrate in X-ray structure of a complex formed by a structurally related glucosyltransferase. " The glutamate residue is located in vicinity to the chloride ion and acts as the acidic catalyst in the reaction. The catalytic site of a-amylases is located in a V-shaped depression on the surface of the enzyme. 

Keywords Molecular modeling NMR spectroscopy Peptide-carbohydrate mimicry Protein-ligand interactions X-ray crystallography... 

In contrast, the existence of peptide-carbohydrate mimicry is more surprising in that it is difficult to picture how these two different classes of compounds could mimic each other. The origin of this effect at the molecular level has been the subject of recent investigations by NMR spectroscopy, X-ray crystallography, and molecular modeling. In combination with functional data, these studies provide insight into the nature of this phenomenon. 

Houk KN, Tantillo DJ, Stanton C, Hu Y (2004) What have Theory and Crystallography Revealed About the Mechanism of Catalysis by Orotidine Monophosphate Decarboxylase 238 1-22 Houseman BT, Mrksich M (2002) Model Systems for Studying Polyvalent Carbohydrate Binding Interactions. 218 1-44 Hricoviniovd Z, see Petrus L (2001) 215 15-41 Hu Y, see Houk KN (2004) 238 1-22... 

The application of crystallography to antibiotic substances that contain carbohydrate residues has been limited by the lack of availability of suitable crystals. 

The successful application of X-ray crystallography of proteins to solution of the structure of lysozyme has been spectacular, but is beyond the scope of this article. However, the enzyme-substrate complexes are of considerable interest, because these substrates and the (structurally similar) inhibitors are carbohydrates. 

X-ray crystallography of lectin-sugar complexes shows the detailed complementarity between the two molecules, which accounts for the strength and specificity of their interactions with carbohydrates. 

This chapter provides a simplified overview of how researchers use the technique of X-ray crystallography to learn macromolecular structures. Chapters 3-8 are simply expansions of the material in this chapter. In order to keep the language simple, I will speak primarily of proteins, but the concepts I describe apply to all macromolecules and macromolecular assemblies that possess ordered structure, including carbohydrates, nucleic acids, and nucleo-protein complexes like ribosomes and whole viruses. 

S S CONTENTS Preface, C. Allen Bush. Methods in Macromo-lecular Crystallography, Andrew J. Howard and Thomas L. Poulos. Circular Dichroism and Conformation of Unordered Polypeptides, Robert W. Woody. Luminescence Studies with Horse Liver Dehydrogenase Information on the Structure, Dynamics, Transitions and Interactions of this Enzyme, Maurice R. Eftink. Surface-Enhanced Resonance Raman Scattering (SERRS) Spectroscopy A Probe of Biomolecular Structure and Bonding at Surfaces, Therese M. Cotton, Jae-Ho Kim and Randall E. Holt. Three-Dimensional Conformations of Complex Carbohydrates, C. Allen Bush and Perse-veranda Cagas. Index. 

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