Figure 4. The α- and β-conformations of the TxLGDP motif. a)
Residues 313-318 (cyan) in PikKS6 form an α-helical turn at the
N-terminal end of α11, in which a hydrogen bond is formed between the
T313 carbonyl and the D317 NH, as observed in all reported structures.
b) ACP-bound docking solutions often show this motif (cyan) making a
type I β-turn, in which hydrogen bonds are formed between the T313
carbonyl and the G316 NH as well as between the T313 hydroxyl group and
the D317 NH and carboxylate. The location of the putative interface
residue L315, whose Cα is shifted 4.7 Å relative to the
α-conformation, is stabilized through a hydrogen bond between its
carbonyl and the hydroxyl group of T381.