De novo design and characterization of an apolar helical hairpin peptide at atomic resolution: Compaction mediated by weak interactions

Design of helical super secondary structural motifs is expected to provide important scaffolds to incorporate functional sites, thus allowing the engi neering of novel miniproteins with function, An alpha,beta -dehydrophenylal anine containing 21-residue apolar peptide was designed to mimic the helica l hairpin motif by using a simple geometrical design strategy. The syntheti c peptide folds into the desired structure as assessed crystallographically at 1.0-Angstrom resolution. The two helices of the helical-hairpin motif, connected by a flexible (Gly)(4) linker, are docked to each other by the co ncerted influence of weak interactions. The folding of the peptide without binary patterning of amino acids, disulfide bonds, or metal ions is a remar kable observation. The results demonstrate that preferred interactions amon g the hydrophobic residues selectively discriminate their putative partners in space, leading to the unique folding of the peptide, also a hallmark of the unique folding of hydrophobic core in globular proteins, We demonstrat e here the engineering of molecules by using weak interactions pointing to their possible further exploitation in the de novo design of protein super secondary structural elements.