95842-07-2Relevant articles and documents
The crystal structure of Z-(Aib)10-OH at 0.65 ? resolution: Three complete turns of 310-helix
Gessmann, Renate,Brückner, Hans,Petratos, Kyriacos
, p. 76 - 81 (2016/02/09)
The synthetic peptide Z-(Aib)10-OH was crystallized from hot methanol by slow evaporation. The crystal used for data collection reflected synchrotron radiation to sub-atomic resolution, where the bonding electron density becomes visible between the non-hydrogen atoms. Crystals belong to the centrosymmetric space group P 1. Both molecules in the asymmetric unit form regular 310-helices. All residues in each molecule possess the same handedness, which is in contrast to all other crystal structure determined to date of longer Aib-homopeptides. These other peptides are C-terminal protected by OtBu or OMe. In these cases, because of the missing ability of the C-terminal protection group to form a hydrogen bond to the residue i-3, the sense of the helix is reversed in the last residue. Here, the C-terminal OH-groups form hydrogen bonds to the residues i-3, in part mediated by water molecules. This makes Z-(Aib)10-OH an Aib-homopeptide with three complete 310-helical turns in spite of the shorter length it has compared with Z-(Aib)11-OtBu, the only homopeptide to date with three complete turns. The synthetic, achiral homo-decapeptide of α-amino-isobutyric acid (Aib) residues crystallizes with two molecules in the asymmetric unit. After refinement at sub-atomic resolution, there is electron density in different Fourier maps, which is clearly visible between non-hydrogen atoms. This is the bonding electron density that is not explained by the usual spheric atom model. In addition, there are second conformations of certain residues that become visible at this ultra-high resolution.
