Orchestration of the functional subsites in the acetylcholinesterase active center – contribution to catalytic perfection and high reactivity toward specific ligands A Shafferman, D Barak, A Ordentlich, N Ariel, C Kronman, D Kaplan, B Velan

Further examination of the functional architecture of the HuAChE active center revealed that reactivity of the enzyme toward substrates and other ligands can also be affected through perturbation of functional domains, which may include multiple subsites in the active center. Thus, enhanced conformational mobility of the catalytic histidine was recently implicated in the activity differences between human butyrylcholinesterase (HuBChE) and the hexamutant HuAChE carrying aliphatic replacements of all the active site gorge aromatic residues (Tyr72, Tyr124, Trp286, Phe295, Phe297, Tyr337) distinguishing between the two

enzymes.9 These include elements of the acyl pocket, the hydrophobic subsite and the PAS. Modulation of ligand interactions with the enzyme can also be affected through disruption of polar networks in the active center. One of these, the ‘hydrogen bond network’, includes residues Tyr133, Glu202, Glu450 as well as two strictly preserved water molecules.10 Another one may include residues Ser229 and the catalytic triad residue Glu334 (A. Shafferman et al., in preparation).