X-Ray Structures of Torpedo Californica Acetylcholinesterase Complexed with (+)-Huperzine a and (-)-Huperzine B: Structural Evidence for an Active Site Rearrangement
Primary Citation of Related Structures: 1EA5, 1GPK, 1GPN
PubMed Abstract:
Kinetic and structural data are presented on the interaction with Torpedo californica acetylcholinesterase (TcAChE) of (+)-huperzine A, a synthetic enantiomer of the anti-Alzheimer drug, (-)-huperzine A, and of its natural homologue (-)-huperzine B. (+)-Huperzine A and (-)-huperzine B bind to the enzyme with dissociation constants of 4 ...
Kinetic and structural data are presented on the interaction with Torpedo californica acetylcholinesterase (TcAChE) of (+)-huperzine A, a synthetic enantiomer of the anti-Alzheimer drug, (-)-huperzine A, and of its natural homologue (-)-huperzine B. (+)-Huperzine A and (-)-huperzine B bind to the enzyme with dissociation constants of 4.30 and 0.33 microM, respectively, compared to 0.18 microM for (-)-huperzine A. The X-ray structures of the complexes of (+)-huperzine A and (-)-huperzine B with TcAChE were determined to 2.1 and 2.35 A resolution, respectively, and compared to the previously determined structure of the (-)-huperzine A complex. All three interact with the "anionic" subsite of the active site, primarily through pi-pi stacking and through van der Waals or C-H.pi interactions with Trp84 and Phe330. Since their alpha-pyridone moieties are responsible for their key interactions with the active site via hydrogen bonding, and possibly via C-H.pi interactions, all three maintain similar positions and orientations with respect to it. The carbonyl oxygens of all three appear to repel the carbonyl oxygen of Gly117, thus causing the peptide bond between Gly117 and Gly118 to undergo a peptide flip. As a consequence, the position of the main chain nitrogen of Gly118 in the "oxyanion" hole in the native enzyme becomes occupied by the carbonyl of Gly117. Furthermore, the flipped conformation is stabilized by hydrogen bonding of Gly117O to Gly119N and Ala201N, the other two functional elements of the three-pronged "oxyanion hole" characteristic of cholinesterases. All three inhibitors thus would be expected to abolish hydrolysis of all ester substrates, whether charged or neutral.
Related Citations:
Residues in Torpedo Californica Acetylcholinesterase Necessary for Processing to a Glycosyl Phosphatidylinositol-Anchored Form Bucht, G., Hjalmarsson, K. (1996) Biochim Biophys Acta 1292: 223
Structure and Dynamics of the Active Site Gorge of Acetylcholinesterase: Synergistic Use of Molecular Dynamics Simulation and X-Ray Crystallography Axelsen, P.H., Harel, M., Silman, I., Sussman, J.L. (1994) Protein Sci 3: 188
Quaternary Ligand Binding to Aromatic Residues in the Active-Site Gorge of Acetylcholinesterase Harel, M., Schalk, I., Ehret-Sabatier, L., Bouet, F., Goeldner, M., Hirth, C., Axelsen, P.H., Silman, I., Sussman, J.L. (1993) Proc Natl Acad Sci U S A 90: 9031
Atomic Structure of Acetylcholinesterase from Torpedo Californica: A Prototypic Acetylcholine-Binding Protein Sussman, J.L., Harel, M., Frolow, F., Oefner, C., Goldman, A., Toker, L., Silman, I. (1991) Science 253: 872
Purification and Crystallization of a Dimeric Form of Acetylcholinesterase from Torpedo Californica Subsequent to Solubilization with Phosphatidylinositol-Specific Phospholipase C Sussman, J.L., Harel, M., Frolow, F., Varon, L., Toker, L., Futerman, A.H., Silman, I. (1988) J Mol Biol 203: 821
Primary Structure of Torpedo Californica Acetylcholinesterase Deduced from its Cdna Sequence Schumacher, M., Camp, S., Maulet, Y., Newton, M., Macphee-Quigley, K., Taylor, S.S., Friedmann, T., Taylor, P. (1986) Nature 319: 407
Organizational Affiliation:
Departments of Structural Biology and Neurobiology, Weizmann Institute of Science, Rehovot 76100, Israel.
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