Structure of the complex of TcAChE with 1-(2-nitrophenyl)-2,2,2- trifluoroethyl-arsenocholine after a 9 seconds annealing to room temperature, during the first 5 seconds of which laser irradiation at 266nm took place
Revelation date
|
20-Nov-2007
Family
|
ACHE: there are 543 genes in this family, 316 structure(s)
Colletier, J.-P., Sanson, B., Royant, A., Specht, A., Nachon, F., Masson, P., Zaccai, G., Sussman, J.L., Goeldner, M., Silman, I., Weik, M., Bourgeois, D
Acetylcholinesterase plays a crucial role in nerve-impulse transmission at cholinergic synapses. The apparent paradox that it displays high turnover despite its active site being buried raises cogent questions as to how the traffic of substrates and products to and from the active site can occur so rapidly in such circumstances. Here, a kinetic crystallography strategy aimed at structurally addressing the issue of product traffic in acetylcholinesterase is presented, in which UV-laser-induced cleavage of a photolabile precursor of the enzymatic product analogue arsenocholine, 'caged' arsenocholine, is performed in a temperature-controlled X-ray crystallography regime. The 'caged' arsenocholine was shown to bind at both the active and peripheral sites of acetylcholinesterase. UV irradiation of a complex with acetylcholinesterase during a brief temperature excursion from 100 K to room temperature is most likely to have resulted in a decrease in occupancy by the caged compound. Microspectrophotometric experiments showed that the caged compound had indeed been photocleaved. It is proposed that a fraction of the arsenocholine molecules released within the crystal had been expelled from both the active and the peripheral sites. Partial q-weighted difference refinement revealed a relative movement of the two domains in acetylcholinesterase after photolysis and the room-temperature excursion, resulting in an increase in the active-site gorge volume of 30% and 35% in monomers A and B of the asymmetric unit, respectively. Moreover, an alternative route to the active-site gorge of the enzyme appeared to open. This structural characterization of acetylcholinesterase 'at work' is consistent with the idea that choline exits from the enzyme after catalysis either via the gorge or via an alternative 'backdoor' trajectory.
Representative scheme of ACHE structure and an image from PDBsum server
Databases
PDB-Sum
2V98 Previously Class, Architecture, Topology and Homologous superfamily - PDB-Sum server
FSSP
2V98Fold classification based on Structure-Structure alignment of Proteins - FSSP server
