The CLN025 Deca-Peptide Retains a β-Hairpin Conformation in Urea and GdmCl

• Published in: The journal of physical chemistry. B Vol. 115; no. 17; pp. 4971 - 4981
• Main Authors: Hatfield, Marcus P. D., Murphy, Richard F., Lovas, Sándor
• Format: Journal Article
• Language: English
• Published: 11.04.2011
• ISSN: 1520-6106; 1520-5207
• DOI: 10.1021/jp111076j

The conformational stability of the β-hairpin miniprotein, CLN025, a variant of chignolin in which the N- and C-terminal Gly are replaced by Tyr, in various concentrations of GdmCl and urea was examined by Molecular Dynamics simulations and Electronic Circular Dichroism (ECD) spectropolarimetry. The peptide maintains its β-hairpin conformation in GdmCl and urea solutions. In GdmCl, Gly7 influences the turn to reduce the number of Asp3-Gly7 H-bonds and the Tyr1-Trp9 H-bond is lost. The structure of the peptide is less stable in 3 M GdmCl than in water or 6 M GdmCl, because the number of Asp3-Thr8 and Tyr1-Tyr10 H-bonds are reduced and the Tyr2 side-chain moves away from the Pro4 and Trp9 side-chains and towards the Tyr10 side-chain. This reduces the number of Tyr2-Pro4 CH-π interactions and Tyr2-Trp9 and Tyr1-Tyr10 aromatic-aromatic (Ar-Ar) interactions and increases the number of Tyr2-Tyr10 Ar-Ar interactions. In 6 M GdmCl at 300 and 333 K, the number of Tyr1-Tyr10 and Asp3-Thr8 H-bonds increases, but fewer structures have Tyr2-Pro4 CH-π and Tyr1-Tyr10 and Tyr2-Trp9 Ar-Ar interactions. In urea, Gly7 is in a mixture of β-turn and random meander structures and the number of Asp3-Thr6 and Tyr1-Tyr10 H-bonds are reduced as are the number of Tyr2-Pro4 CH-π interactions and Tyr1-Tyr10 and Tyr2-Trp9 Ar-Ar interactions. In 4 M urea, a shorter turn places Gly7 in to the β-sheet region and Tyr10 is pushed out into the solvent. In 8 M urea, the number of Asp3-Glu5 H-bonds is increased and the β-sheet is lost, but the electrostatic interaction between the charged termini is restored and a cation-π interaction between the indolyl ring of Trp9 and the positively charged N-terminus is formed. In 8 M urea at 333 K, the β-hairpin conformation is almost lost. The structure of CLN025 is stable, because the weakly polar interactions and H-bonds maintain the β-hairpin conformation in the various environments. CLN025 should not be considered a miniprotein, because it lacks a well-defined tertiary structure, it is resistant to denaturation, does not have an increased heat capacity near its melting temperature and the structures near and above the melting temperature retain a β-hairpin conformation.