Model systems for beta-hairpins and beta-sheets.

beta-Sheets and alpha-helices are the two principal secondary structures in proteins. However, our understanding of beta-sheet structure lags behind that of alpha-helices, largely because, until recently, there was no model system to study the beta-sheet secondary structure in isolation. With the development of well-folded beta-hairpins, this is changing rapidly. Recent advances include: increased understanding of the relative contributions of turn, strand and sidechain interactions to beta-hairpin and beta-sheet stability, with the role of aromatic residues as a common subtheme; experimental and theoretical kinetic and thermodynamic studies of beta-hairpin and beta-sheet folding; de novo protein design, including all-beta structures, mixed alpha/beta motifs and switchable systems; and the creation of functional beta-hairpins.