title: Factors involved in the stability of isolated beta-sheets: Turn sequence, beta-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 beta-sheet in aqueous solution. To improve our beta-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' beta-turns. The analysis of several NMR parameters, NOE data, as well as Deltadelta(CalphaH), DeltadeltaC(beta), and Deltadelta(Cbeta) values, demonstrates that the new peptide forms a beta-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 beta-hairpin-forming peptides showing the essential role of the turn sequence for beta-hairpin folding. The well-defined beta-sheet motif calculated for the new designed peptide (pair-wise RMSD for backbone atoms is 0.5 +/- 0.1 A) displays a high degree of twist. This twist likely contributes to stability, as a more hydrophobic surface is buried in the twisted beta-sheet than in a flatter one. The twist observed in the up-and-down antiparallel beta-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 beta-sheet twisting relative to a "flat" beta-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.
authors.affiliation: Instituto de Química-Física Rocasolano, Consejo Superior de Investigaciones Científicas, Serrano 119, 28006 Madrid, Spain.
authors.forename: Clara M
authors.initials: CM
authors.lastname: Santiveri
authors.forename: Jorge
authors.initials: J
authors.lastname: Santoro
authors.forename: Manuel
authors.initials: M
authors.lastname: Rico
authors.forename: M Angeles
authors.initials: MA
authors.lastname: Jiménez
mesh_terms: D000595:Amino Acid Sequence; D057927:Hydrophobic and Hydrophilic Interactions; D008958:Models, Molecular; D008969:Molecular Sequence Data; D019906:Nuclear Magnetic Resonance, Biomolecular; D010455:Peptides / Q000737:chemistry*; D017433:Protein Structure, Secondary; D013816:Thermodynamics; D014867:Water
chemical_list: D010455:Peptides; D014867:Water