Conformational investigation of designed short linear peptides able to fold into β-hairpin structures in aqueous solution

Backgound:Formation of secondary structure plays an important role in the early stages of protein folding. The conformational analysis of designed peptides has proved to be very useful for identifying the interactions responsible for the formation and stability of α-helices. However, very little is known about the factors leading to the formation of β-hairpins. In order to get a good β-hairpin-forming model peptide, two peptides were designed on the basis of β-sheet propensities and individual statistical probabilities in the turn sites, together with solubility criteria. The conformational properties of the two peptides were analyzed by two-dimensional NMR methods.ResultsLong-range cross-correlations observed in NOE and ROE spectra, together with other NMR evidence, show that peptide IYSNPDGTWT forms a highly populated β-hairpin in aqueous solution with a type I β-turn plus a G1 β-bulge conformation in the chain-bend region. The analogous peptide with a Pro5 substituted by Ser forms, in addition to the previous conformation, a second β-hairpin with a standard type I β-turn conformation, and the two forms are in fast dynamic equilibrium with one another. The effect of pH demonstrates the existence of a stabilizing interaction between the Asn and Asp sidechains. The populations of β-hairpin conformations increase in the presence of trifluoroethanol (a structure-enhancing solvent). On the other hand, some residual structure persists at a high denaturant concentration (8 M urea).ConclusionThis work highlights the importance of the β-turn residue composition in determining the particular type of β-hairpin adopted by a peptide, though a role of interstrand sidechain interactions in the stabilization of the formed β-hairpin is not discarded. The fact that trifluoroethanol can stabilize α-helices or β-hairpins depending on the intrinsic properties of the peptide sequence is again shown. An additional example of the presence of residual structure under denaturing conditions is also presented