Structure Of Butyrylcholinesterase Research Articles

Molecular docking of different inhibitors and activators to butyrylcholinesterase

There are three major active sites of butyrylcholinesterase: catalytic site, peripheral site, and activator site. In this study, pseudosubstrate inhibitors, 1,3,5-alkylcarbamyloxybenzenes (1–11), were designed as the catalytic site directed inhibitors of the enzyme. Automated docking of 1,3,5-tri-n-octylcarbamyloxybenzene 1 into the X-ray crystal structure of butyrylcholinesterase suggested that the configuration of the inhibitor in the enzyme complex is in the (1,3,5)-(cis,trans,trans)-form. Thus, the cis n-octylcarbamyl group of 1 extended itself to the peripheral site; furthermore, two trans n-octylcarbamyl moieties of 1 shielded W82 of the anionic site. 5-N-n-Butylcarbamyloxyresorcinol (12) was further used to characterize the butyryl group binding site of the catalytic site. Automated docking of 12 into the enzyme showed that the best bound rotamer of the inhibitor in the enzyme complex was the trans form. Moreover, the butylcarbamyl moiety of 12 was bound well into the butyryl group binding site of the enzyme. Docking of cage amines into the enzyme indicated that these compounds were bound into the peripheral site of the enzyme. We also found that a small cave, located outside the enzyme around A277-Y282, might play an important role in the activation of the enzyme. Two activators of butyrylcholinesterase, n-butyl-N-carbamyloxy-3,3-dimethylbutane and 2,4,6-trinitrotoluene, were docked well into the above-mentioned cave.

Why has butyrylcholinesterase been retained? Structural and functional diversification in a duplicated gene

While acetylcholinesterase (EC 3.1.1.7) has a clearly defined role in neurotransmission, the functions of its sister enzyme butyrylcholinesterase (EC 3.1.1.8) are more obscure. Numerous mutations, many inactivating, are observed in the human butyrylcholinesterase gene, and the butyrylcholinesterase knockout mouse has an essentially normal phenotype, suggesting that the enzyme may be redundant. Yet the gene has survived for many millions of years since the duplication of an ancestral acetylcholinesterase early in vertebrate evolution. In this paper, we ask the questions: why has butyrylcholinesterase been retained, and why are inactivating mutations apparently tolerated? Butyrylcholinesterase has diverged both structurally and in terms of tissue and cellular expression patterns from acetylcholinesterase. Butyrylcholinesterase-like activity and enzymes have arisen a number of times in the animal kingdom, suggesting the usefulness of such enzymes. Analysis of the published literature suggests that butyrylcholinesterase has specific roles in detoxification as well as in neurotransmission, both in the brain, where it appears to control certain areas and functions, and in the neuromuscular junction, where its function appears to complement that of acetylcholinesterase. An analysis of the mutations in human butyrylcholinesterase and their relation to the enzyme’s structure is shown. In conclusion, it appears that the structure of butyrylcholinesterase’s catalytic apparatus is a compromise between the apparently conflicting selective demands of a more generalised detoxifier and the necessity for maintaining high catalytic efficiency. It is also possible that the tolerance of mutation in human butyrylcholinesterase is a consequence of the detoxification function. Butyrylcholinesterase appears to be a good example of a gene that has survived by subfunctionalisation.

Crystal Structure of Human Butyrylcholinesterase and of Its Complexes with Substrate and Products

Cholinesterases are among the most efficient enzymes known. They are divided into two groups: acetylcholinesterase, involved in the hydrolysis of the neurotransmitter acetylcholine, and butyrylcholinesterase of unknown function. Several crystal structures of the former have shown that the active site is located at the bottom of a deep and narrow gorge, raising the question of how substrate and products enter and leave. Human butyrylcholinesterase (BChE) has attracted attention because it can hydrolyze toxic esters such as cocaine or scavenge organophosphorus pesticides and nerve agents. Here we report the crystal structures of several recombinant truncated human BChE complexes and conjugates and provide a description for mechanistically relevant non-productive substrate and product binding. As expected, the structure of BChE is similar to a previously published theoretical model of this enzyme and to the structure of Torpedo acetylcholinesterase. The main difference between the experimentally determined BChE structure and its model is found at the acyl binding pocket that is significantly bigger than expected. An electron density peak close to the catalytic Ser(198) has been modeled as bound butyrate.