Kinetic and structural studies on the interaction of cholinesterases with the anti-Alzheimer drug rivastigmine.
Rivastigmine, a carbamate inhibitor of acetylcholinesterase, is already in use for treatment of Alzheimer's disease under the trade name of Exelon. Rivastigmine carbamylates Torpedo californica acetylcholinesterase very slowly (k(i) = 2.0 M(-1) min(-1)), whereas the bimolecular rate constant for inhibition of human acetylcholinesterase is >1600-fold higher (k(i) = 3300 M(-1) min(-1)). For human butyrylcholinesterase and for Drosophila melanogaster acetylcholinesterase, carbamylation is even more rapid (k(i) = 9 x 10(4) and 5 x 10(5) M(-1) min(-1), respectively). Spontaneous reactivation of all four conjugates is very slow, with <10% reactivation being observed for the Torpedo enzyme after 48 h. The crystal structure of the conjugate of rivastigmine with Torpedo acetylcholinesterase was determined to 2.2 A resolution. It revealed that the carbamyl moiety is covalently linked to the active-site serine, with the leaving group, (-)-S-3-[1-(dimethylamino)ethyl]phenol, being retained in the "anionic" site. A significant movement of the active-site histidine (H440) away from its normal hydrogen-bonded partner, E327, was observed, resulting in disruption of the catalytic triad. This movement may provide an explanation for the unusually slow kinetics of reactivation.
Bar-On
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Departmentof Neurobiology, Weizmann Institute of Science, Rehovot 76100, Israel.
Millard
C B
CB
Harel
M
M
Dvir
H
H
Enz
A
A
Sussman
J L
JL
Silman
I
I
D000110:Acetylcholinesterase / Q000737:chemistry / Q000378:metabolism*; D000818:Animals; D001665:Binding Sites; D002219:Carbamates / Q000378:metabolism*; D002800:Cholinesterase Inhibitors / Q000378:metabolism*; D002942:Circular Dichroism; D018360:Crystallography, X-Ray; D004331:Drosophila melanogaster; D004789:Enzyme Activation; D007700:Kinetics; D018696:Neuroprotective Agents / Q000378:metabolism*; D048448:Phenylcarbamates; D011487:Protein Conformation; D000068836:Rivastigmine; D013050:Spectrometry, Fluorescence; D013056:Spectrophotometry, Ultraviolet; D014101:Torpedo
D002219:Carbamates; D002800:Cholinesterase Inhibitors; D018696:Neuroprotective Agents; D048448:Phenylcarbamates; D000110:Acetylcholinesterase; D000068836:Rivastigmine