1. Solvent Polarity Controls the Helical Conformation of Short Peptides Rich in Cα-Tetrasubstituted Amino Acids
- Author
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Quirinus B. Broxterman, Silvano Geremia, Lucio Randaccio, Nicola Demitri, Paolo Scrimin, Massimo Bellanda, Bernard Kaptein, Lucia Pasquato, Paolo Pengo, Stefano Mammi, Bellanda, M., Mammi, S., Geremia, Silvano, Demitri, Nicola, Randaccio, Lucio, Broxterman, Q. B., Kaptein, B., Pengo, Paolo, Pasquato, Lucia, and Scrimin, P.
- Subjects
Models, Molecular ,Circular dichroism ,helical structures ,NMR spectroscopy ,peptides ,Solvent effects ,Polarity (physics) ,Stereochemistry ,solvent effects ,Crystallography, X-Ray ,Protein Structure, Secondary ,Catalysis ,chemistry.chemical_compound ,Molecular dynamics ,Amino Acids ,Nuclear Magnetic Resonance, Biomolecular ,chemistry.chemical_classification ,solvent effect ,Molecular Structure ,Chemistry ,Circular Dichroism ,Methanol ,structure elucidation ,Organic Chemistry ,Temperature ,Hydrogen Bonding ,Trifluoroethanol ,General Chemistry ,Nuclear magnetic resonance spectroscopy ,peptide ,Amino acid ,Solvent ,helical structure ,Solvents ,Oligopeptides - Abstract
The two peptides, rich in C(alpha)-tetrasubstituted amino acids, Ac-[Aib-L-(alphaMe)Val-Aib](2)-L-His-NH(2) (1) and Ac-[Aib-L-(alphaMe)Val-Aib](2)-O-tBu (2 a) are prevalently helical. They present the unique property of changing their conformation from the alpha- to the 3(10)-helix as a function of the polarity of the solvent: alpha in more polar solvents, 3(10) in less polar ones. Conclusive evidence of this reversible change of conformation is reported on the basis of the circular dichroism (CD) spectra and a detailed two-dimensional NMR analysis in two solvents (trifluoroethanol and methanol) refined with molecular dynamics calculations. The X-ray diffractometric analysis of the crystals of both peptides reveals that they assume a prevalent 3(10)-helix conformation in the solid state. This conformation is practically superimposable on that obtained from the NMR analysis of 1 in methanol. The NMR results further validate the reported CD signature of the 3(10)-helix and the use of the CD technique for its assessment.
- Published
- 2007
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