Artist impression of the interaction between CBP21 and chitin (side view, left; top view, right). The picture highlights how the flat surface of CBP21 fits the flat surface of a β-chitin crystal (the binding interaction is hypothetical and has not been modelled). The surfaces of residues known to interact with chitin  are coloured magenta and the side chains of these residues are shown. In the side view some of the magenta surface is hidden by the white surface of other residues. Please note that the actual orientation of the enzyme relative to the substrate is unknown; see  for an interesting discussion of this topic.