The longest, regular polypeptide 3(10)-helix at atomic resolution

A synthetic, terminally blocked homodecapeptide from the C-alpha, alpha-dimethylated glycyl residue alpha-aminoisobutyric acid has been analyzed by single-crystal X-ray diffraction and the structure refined to R = 0.073. The compound crystallizes as a perfect 3(10)-helix, stabilized by eight consecutive intramolecular N-H . . . O = C hydrogen bonds. This is the first observation at atomic resolution of a regular polypeptide 3(10)-helix as long as three complete turns.