Solid-State NMR and Calorimetry of Structural Waters in Helical Peptides

The peptide hydrates Gly-Gly-Val·2H2O (GGV) and Gly-Ala-Leu·3H2O (GAL) are known to adopt α-helical configurations containing waters of hydration in which each water is H-bonded to three or four peptide groups. Herein we report a thermodynamic and solid-state NMR (2H and 17O) study of these peptides...

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Bibliographic Details
Published in:Journal of the American Chemical Society 2002-03, Vol.124 (10), p.2345-2351
Main Authors: Pometun, Maxim S, Gundusharma, Usha M, Richardson, John F, Wittebort, Richard J
Format: Article
Language:English
Subjects:
Biological and medical sciences
Calorimetry, Differential Scanning
Crystallography, X-Ray
Fundamental and applied biological sciences. Psychology
Hydrogen Bonding
Intermolecular dynamics
Intermolecular phenomena
Models, Molecular
Molecular biophysics
Nuclear Magnetic Resonance, Biomolecular - methods
Oligopeptides - chemistry
Protein Structure, Secondary
Thermodynamics
Water - chemistry
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Summary:The peptide hydrates Gly-Gly-Val·2H2O (GGV) and Gly-Ala-Leu·3H2O (GAL) are known to adopt α-helical configurations containing waters of hydration in which each water is H-bonded to three or four peptide groups. Herein we report a thermodynamic and solid-state NMR (2H and 17O) study of these peptides. From TGA and DSC, the average enthalpy per H-bond is 15 kJ/mol. The dynamics and average orientation of the hydrate are studied by powder and single-crystal 2H NMR. Whereas waters that are shown by the X-ray structure to be coordinated by four hydrogen bonds do not yield observable 2H NMR signals at room temperature, two of the three triply coordinated waters yield residual 2H quadrupole coupling tensors characteristic of rapid 180° flip motions and the orientation of the residual tensor is that expected from the X-ray structure-derived H-bonding pattern. At −65 °C, the flip motions of triply coordinated water in GGV slow into the 2H NMR intermediate exchange regime whereas the tetrahedrally coordinated water approaches the slow-exchange limit and yields an observable NMR signal. Extensive isotope exchange between water vapor and crystalline GGV establishes the presence of additional hydrate dynamics and solid-state proton transfer along a chain of water-bridged protonated α-amino groups.
ISSN:0002-7863
1520-5126
DOI:10.1021/ja017364r