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.