FIGURE 1.

Diagram showing the locations of the associating surfaces within spirals formed by members to the nitrilase superfamily. Monomers are represented by rectangles. These monomers associate to form dimers at the A-surface in all superfamily members. The dimers associate to form helical assemblies by associating across the C-surface. Two dimers are shown per turn in (A). In some superfamily members such as CynD interactions occur across the groove leading to the formation of the D-surface between adjacent turns of the spiral. In CynD, alternative interactions across the groove leading to the formation of the E-surface (B) cause to the termination of the spirals after a fixed number of dimers.