Folding of an Ala-Ala-Ala tripeptide into a beta-turn via hydrophobic encapsulation

An Ac-Ala-Ala-Ala-NH2 tripeptide was folded into a beta-turn structure even in water through hydrophobic binding by a self-assembled porphyrin cage. The turn conformation of the bound peptide was fully assigned from NOESY measurements and was strongly supported by molecular dynamics simulation. Single mutation experiments and molecular modeling also suggested that CH-pi interactions between methyl groups of Ala residues and porphyrin ligands were important for the stabilization of the turn conformation. Furthermore, we observed the induction of a beta-hairpin structure by encapsulation of a heptapeptide, Ac-Gly-Gly-Ala-Ala-Ala-Gly-Gly-NH2, possessing Ala-Ala-Ala sequence at the middle.