engleski

Efficiency of oximes in reactivation of phosphorylated AChE is limited by their interactions with the AChE peripheral alosteric site

Acetylcholinesterase (AChE, EC 3.1.1.7) presents an important enzyme in the cholinergic neurotransmission. Its specific active site is the primary target of organophosphorus compounds (OP) like pesticides and nerve agents. Namely, OPs inhibit AChE by phosphorylating its catalytic serine in the active site. Such inactivation of AChE leads to a series of life threatening manifestations which calls for a fast medical response. Currently, compound known as oximes, that have the ability to dephosphorylate AChE, are used as antidotes. Even if there is an ongoing discussion on oximes efficiency, they are still the mainstay of the post OP-exposure treatment. In the search for more efficient oxime an important step presents understanding of its interactions within the active site of phosphorylated AChE. Therefore, AChE site-directed mutants provide a powerful tool for such investigation. In here presented study we evaluated reactivation of five nerve agent tabun phosphorylated AChE mutants by newly developed bispyridinium oximes. We selected site-directed mutants with mutations at the choline binding site (Y337A, F338A), the acyl pocket (F295L) and the peripheral binding site (Y124Q, W286A) to get an overview of possible interactions. Moreover, interactions of oximes with active site amino acids were evaluated using the molecular docking technique. Our results indicated that substitution of the aromatic amino acids with aliphatic ones in the choline binding site and the acyl pocket negatively influenced reactivation by bispyridinium oximes. These changes probably opened up a space for oximes to form stable interactions with other present aromatic residues, which resulted in increased affinity for these oximes but lower reactivation rates. It can be concluded that selected aromatic residues are important for placing bispyridinium oximes in the right position to the phosphorylated active site serine. On the other hand, disruption of the π-π sandwich formed between one of the oxime pyridinium rings and the amino acids of the peripheral site (i.e. Y124Q, W286A), allowed oximes to get into the more favourable position for nucleophilic attack on the phosphylated catalytic serine. In this case, reactivation rates increased 2-5 times compared to w.t. AChE. Therefore, it seems that aromatic amino acids at the AChE peripheral site present limitation in bispyridinium oxime reactivation efficiency.

organophosphorus compounds ; AChE ; mutants ; inhibition ; tabun ; reactivation

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