Consensus sequence and three-dimensional model of ankyrin module. (A), Sequence comparison between the consensus DARPin repeat motif and the repeat motif of our ankyrin library. The red letters refer to the positions of random amino acids, and blue letters represent the residues which differ from the consensus DARPin sequence. The position of the recognition site for the restriction nuclease Bsm BI is underlined. (B), Structural model of one single ankyrin repeat motif (or module). (C), Spatial arrangement of three modules belonging to the same ankyrin linear sequence (triple-repeat motif ankyrin molecule). The fixed structure of the repeat motif is presented as a yellow ribbon. The variable amino acids on the solvent-exposed surface are shown as stick pattern; their respective number in the linear sequence is indicated in panel B.