Interactions Responsible for the pH Dependence of the β‐Hairpin Conformational Population Formed by a Designed Linear Peptide

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Abstract
In a previous work [Blanco, F. J., Jiménez, M. A., Herranz, J., Rico, M., Santoro, J. & Nieto, J. L. (1993) J. Am. Chem. Soc. 115, 5887–5888] we showed that a short, designed linear peptide, YQNPDG-SQA (peptide 1), can form a monomeric β hairpin in aqueous solution. The pH dependence of the β-hairpin conformation formed by the designed peptide and a series of related peptides has been examined in this work using 1H-NMR methods. Three pH-dependent interactions have been identified: a local interaction, unimportant structurally, between the C-terminal carboxylate group and the side-chain amide group of Q8; an electrostatic interaction between the main-chain N-terminus and C-terminus; and a hydrogen bond involving the side-chain amide protons of N3 and the side-chain carboxylate group of D5. The latter two interactions are particularly relevant as they increase the population of the β-hairpin conformation. We also observe in the mutant peptide A9H that the interaction between Y1 and H9 (of the type proposed to exist in proteins) does not contribute to β-hairpin stabilisation in our peptide system. Peptide 1 is, therefore, a very suitable model to examine the different interactions that contribute to β-hairpin stability.

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