This work aimed at watching acetylcholinesterase (AChE) 'at work'. AChE is a very rapid enzyme and terminates the transmission of the nervous influx at cholinergic synapses. Conformational substates of Torpedo californica (Tc) AChE were trapped in x-ray crystallography structures of the enzyme in complex with putative anti-Alzheimer drugs. Structures of both nonaged and aged conjugates of TcAChE and soman were solved, which allowed to shed light on the mechanism of aging in organophosphate (OP) - inhibited AChE. The structure of the ternary complex of the nonaged conjugate and a reactivator was solved. All those structures will help designing new AChE-targeted drugs (anti-Alzheimer drugs or antidotes against OP poisoning) by taking into account flexibility and minor conformations of the enzyme. The structure of TcAChE in complex with the peripheral site (PAS) inhibitor aflatoxin B1 was solved in two crystal forms. This work revealed crystallography artifacts that should be avoided for correct biological interpretation. Measurement of the phosphorescence lifetime of AB1 allowed probing PAS dynamics on the timescale of seconds, thereby highlighting differential flexibility in two distinct crystal packing environments of TcAChE. This spectroscopic method is proposed as a complementary tool for kinetic crystallography experiments. An optimal cryogenic temperature range was identified, which could help exploring the reaction mechanisms of AChE by slowing down the enzyme motions without freezing them.
