NMR investigations of protein-carbohydrate interactions: refined three- dimensional structure of the complex between hevein and methyl beta- chitobioside |
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Authors: | Asensio JL; Canada FJ; Bruix M; Gonzalez C; Khiar N; Rodriguez-Romero A; Jimenez-Barbero J |
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Institution: | Instituto de Quimica Organica General, CSIC, Madrid, Spain. |
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Abstract: | The specific interaction of hevein with GlcNAc-containing oligosaccharides
has been analyzed by1H-NMR spectroscopy. The association constants for the
binding of hevein to a variety of ligands have been estimated from1H-NMR
titration experiments. The association constants increase in the order
GlcNAc-alpha(1-->6)-Man < GlcNAc < benzyl-beta-GlcNAc <
p-nitrophenyl-beta-GlcNAc < chitobiose < p-
nitrophenyl-beta-chitobioside < methyl-beta-chitobioside <
chitotriose. Entropy and enthalpy of binding for different complexes have
been obtained from van't Hoff analysis. The driving force for the binding
process is provided by a negative DeltaH0which is partially compensated by
negative DeltaS0. These negative signs indicate that hydrogen bonding and
van der Waals forces are the major interactions stabilizing the complex.
NOESY NMR experiments in water solution provided 475 accurate protein
proton-proton distance constraints after employing the MARDIGRAS program.
In addition, 15 unambiguous protein/carbohydrate NOEs were detected. All
the experimental constraints were used in a refinement protocol including
restrained molecular dynamics in order to determine the highly refined
solution conformation of this protein- carbohydrate complex. With regard to
the NMR structure of the free protein, no important changes in the protein
nOe's were observed, indicating that carbohydrate-induced conformational
changes are small. The average backbone rmsd of the 20 refined structures
was 0.055 nm, while the heavy atom rmsd was 0.116 nm. It can be deduced
that both hydrogen bonds and van der Waals contacts confer stability to the
complex. A comparison of the three-dimensional structure of hevein in
solution to those reported for wheat germ agglutinin (WGA) and hevein
itself in the solid state has also been performed. The polypeptide
conformation has also been compared to the NMR-derived structure of a
smaller antifungical peptide, Ac-AMP2.
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