Dawn Wong - Acetylcholinesterase complexed with bivalent ligands related to huperzine A: experimental evidence for species-dependent protein-ligand complementarity

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      Publication Details (including relevant citation   information):

      Wong, D. M.; Greenblatt, H. M.; Dvir, H.;   Carlier, P. R.; Han, Y.-F.; Pang, Y.-P.; Silman, I.; Sussman, J.   L.

      Acetylcholinesterase complexed with bivalent ligands related to   huperzine A: experimental evidence for species-dependent   protein-ligand complementarity.

      Journal of the American Chemical Society  2003, 125, 363-373.

      PMID: 12517147. http://dx.doi.org/10.1021/ja021111w



      Acetylcholinesterase (AChE) inhibitors improve the cognitive   abilities of Alzheimer patients. (-)-Huperzine A [(-)-HupA], an   alkaloid isolated from the club moss, Huperzia serrata,   is one such inhibitor, but the search for more potent and   selective drugs continues. Recently alkylene-linked dimers of   5-amino-5,6,7,8-tetrahydroquinolinone (hupyridone,   1a), a fragment of HupA, were shown to serve as   more potent inhibitors of AChE than (-)-HupA and monomeric   1a. We soaked two such dimers,   (S,S)-(-)-bis(10)-hupyridone   [(S,S)-(-)-2a] and   (S,S)-(-)-bis(12)-hupyridone   [(S,S)-(-)-2b] containing,   respectively, 10 and 12 methylenes in the spacer, into trigonal   TcAChE crystals, and solved the X-ray structures of the   resulting complexes using the difference Fourier technique, both   to 2.15 Å resolution. The structures revealed one HupA-like   1a unit bound to the 'anionic' subsite of the   active-site, near the bottom of the active-site gorge, adjacent   to Trp84, as seen for the TcAChE/(-)-HupA complex, and   the second 1a unit near Trp279 in the   'peripheral' anionic site at the top of the gorge, both bivalent   molecules thus spanning the active-site gorge. The results   confirm that the increased affinity of the dimeric HupA analogs   for AChE is conferred by binding to the two 'anionic' sites of   the enzyme. Inhibition data show that (-)-2a  binds to TcAChE ~6-7- and > 170-fold more tightly   than (-)-2b and (-)-HupA, respectively. In   contrast, previous data for rat AChE show that   (-)-2b binds ~3- and ~2-fold more tightly than   (-)-2a and (-)-HupA, respectively. Structural   comparison of TcAChE with rat AChE, as represented by   the closely related mouse AChE structure (1maa.pdb), reveals a   narrower gorge for rat AChE, a perpendicular alignment of the   Tyr337 ring to the gorge axis, and its conformational rigidity,   as a result of hydrogen bonding between its hydroxyl group and   that of Tyr341, relative to TcAChE Phe330. These   structural differences in the active-site gorge explain the   switch in inhibitory potency of (-)-2a and   2b and the larger dimer/(-)-HupA potency ratios   observed for TcAChE relative to rat AChE. The results   offer new insights into factors affecting protein-ligand   complementarity within the gorge and should assist the further   development of improved AChE inhibitors.

      Address (URL): http://dx.doi.org/10.1021/ja021111w