Figure 4

Relative entropy analysis of canonical positions in 15,497 Ank repeats. (a) The positional relative entropies are shown with secondary structural elements noted (grey arrows are β-strands). Blue and green arrows indicate the most variable positions; asterisks (*) indicate positions mutated by the Plückthun lab to alter Ank-domain specificity. (b) The location of the binding site in a single Ank repeat in the loop and proximal α-helical surface is labeled. (c) The 4-Ank domain from GABPβ1 (spheres) is shown bound to the ligand GABPα (ribbons) in two views from 180° rotation. Again, the binding surface is evident from the low relative entropies. Note that some non-binding surface-exposed positions, particularly turn residues, are conserved due to their importance in defining the Ank fold. Some positions in GABPβ1 do not map onto the canonical Ank sequence and are colored grey. Rendered using PyMOL from PDB entry 1AWC.