The Crystal Structure of a Complex of Acetylcholinesterase with a Bis-(-)-nor-meptazinol Derivative Reveals Disruption of the Catalytic Triad

A bis-(-)-nor-meptazinol derivative in which the two meptazinol rings are linked by a nonamethylene spacer is a novel acetylcholinesterase inhibitor that inhibits both catalytic activity and A beta peptide aggregation. The crystal structure of its complex with Torpedo californica acetylcholinesterase was determined to 2.7 angstrom resolution. The ligand spans the active-site gorge, with one nor-meptazinol moiety bound at the anionic subsite of the active site, disrupting the catalytic triad by forming a hydrogen bond with His440N(epsilon 2), which is hydrogen-bonded to Ser2000(gamma) in the native enzyme. The second nor-meptazinol binds at the peripheral anionic site at the gorge entrance. A number of GOLD models of the complex, using both native TcAChE and the protein template from the crystal structure of the bis-(-)-nor-meptazinol/TcAChE complex, bear higher similarity to the X-ray structure than a previous model obtained using the mouse enzyme structure. These findings may facilitate rational design of new meptazinol-based acetylcholinesterase inhibitors.