Acetylcholinesterase in motion: visualizing conformational changes in crystal structures by a morphing procedure.

In order to visualize and appreciate conformational changes between homologous three-dimensional (3D) protein structures or protein/inhibitor complexes, we have developed a user-friendly morphing procedure. It enabled us to detect coordinated conformational changes not easily discernible by analytic methods or by comparison of static images. This procedure was applied to comparison of native Torpedo californica acetylcholinesterase and of complexes with reversible inhibitors and conjugates with covalent inhibitors. It was likewise shown to be valuable for the visualization of conformational differences between acetylcholinesterases from different species. The procedure involves generation, in Cartesian space, of 25 interpolated intermediate structures between the initial and final 3D structures, which then serve as the individual frames in a QuickTime movie.