Interruption of a 3 10 ‐helix by a single Gly residue in a poly‐Aib motif: A crystallographic study

The structural influence of a single Gly residue inserted into an Aib 16 homooligomer was studied in the solid state by X‐ray crystallography. The peptides N 3 Aib 8 GlyAib 8 PheNH 2 ( 1 ) and CbzPheAib 8 GlyAib 8 ( 2 ) were found to adopt well‐defined helical structures, which are broadly 3 10 helical. Indeed, 2 is the longest crystallographic 3 10 helix thus far reported. However, in the region of the central Gly residue, a loosening of the 3 10 structure is observed in both peptides, with 1 clearly showing local adoption of an α‐helical structure in the region of residues 7–9. © 2010 Wiley Periodicals, Inc. Biopolymers 95: 62–69, 2011.