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

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. Copyright © 1995, Wiley Blackwell. All rights reserved