Factors involved in the stability of isolated β‐sheets: Turn sequence, β‐sheet twisting, and hydrophobic surface burial

Abstract

We have recently reported on the design of a 20‐residue peptide able to form a significant population of a three‐stranded up‐and‐down antiparallel β‐sheet in aqueous solution. To improve our β‐sheet model in terms of the folded population, we have modified the sequences of the two 2‐residue turns by introducing the segment DPro‐Gly, a sequence shown to lead to more rigid type II′ β‐turns. The analysis of several NMR parameters, NOE data, as well as Δδ CαH , ΔδC β , and Δδ Cβ values, demonstrates that the new peptide forms a β‐sheet structure in aqueous solution more stable than the original one, whereas the substitution of the DPro residues by LPro leads to a random coil peptide. This agrees with previous results on β‐hairpin‐forming peptides showing the essential role of the turn sequence for β‐hairpin folding. The well‐defined β‐sheet motif calculated for the new designed peptide (pair‐wise RMSD for backbone atoms is 0.5 ± 0.1 Å) displays a high degree of twist. This twist likely contributes to stability, as a more hydrophobic surface is buried in the twisted β‐sheet than in a flatter one. The twist observed in the up‐and‐down antiparallel β‐sheet motifs of most proteins is less pronounced than in our designed peptide, except for the WW domains. The additional hydrophobic surface burial provided by β‐sheet twisting relative to a “flat” β‐sheet is probably more important for structure stability in peptides and small proteins like the WW domains than in larger proteins for which there exists a significant contribution to stability arising from their extensive hydrophobic cores.