De novo design of a monomeric three-stranded antiparallel beta-sheet

Here we describe the NMR conformational study of a 20-residue linear peptid e designed to fold into a monomeric three-stranded antiparallel beta-sheet in aqueous solution. Experimental and statistical data on amino acid beta-t urn and beta-sheet propensities, cross-strand side-chain interactions, solu bility criteria, and our previous experience with beta-hairpins were consid ered for a rational selection of the peptide sequence. Sedimentation equili brium measurements and NMR dilution experiments provide evidence that the p eptide is monomeric. Analysis of H-1 and C-13-NMR parameters of the peptide , in particular NOEs and chemical shifts, and comparison with data obtained for two 12-residue peptides encompassing the N- and C-segments of the desi gned sequence indicates that the 20-residue peptide folds into the expected conformation. Assuming a two-state model, the exchange kinetics between th e beta-sheet and the unfolded peptide molecules is in a suitable range to e stimate the folding rate on the basis of the NMR linewidths of several reso nances. The time constant for the coil-beta-sheet transition is of the orde r of several microseconds in the designed peptide. Future designs based on this peptide system are expected to contribute greatly to our knowledge of the many factors involved in beta-sheet formation and stability.