Localization of a novel adhesion-promoting site on acetylcholinesterase using catalytic antiacetylcholinesterase antibodies displaying cholinesterase-like activity |
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Authors: | Glynis Johnson Samuel W Moore |
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Institution: | (1) Departments of Pediatric Surgery and Medical Biochemistry, Faculty of Medicine, University of Stellenbosch, P.O. Box 19063, 7505 Tygerberg, South Africa |
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Abstract: | A monoclonal antibody (MAb) raised against human acetylcholinesterase was found to have catalytic activity. A similar phenomenon
was observed in a polyclonal antibody raised against the same antigen. The antibodies were demonstrated to be pure, and no
contamination with either acetylcholinesterase or butyrylcholinesterase was found. Both antibodies hydrolyzed acetylthiocholine,
anacetylcholinesterasesubstrate, and the MAb followed Michaelis-Menten kinetics. Six other MAbs and one other polyclonal antibody
showed no evidence of catalytic activity.
Acetylcholinesterase is a key component in the transmission of the nerve impulse, and is also expressed nonsynaptically during
embryonic development, and abnormalities in expression are seen in neural tumors and degenerative disorders. This unusual
expression is believed to be associated with a novel function of the enzyme related to differentiation and cell adhesion.
Autoantibodies to acetylcholinesterase have been observed in a variety of neurologic, muscular, and autoimmune disorders.
In an investigation of the possible role of acetylcholinesterase in cell adhesion, we showed that the enzyme promoted neurite
outgrowth, in neuroblastoma cell lines, and conversely, that certain antiacetylcolinesterase antibodies abrogated cell-substrate
adhesion. Interestingly, the antibodies most effective in this regard were catalytic. Preliminary epitopeanalysis indicated
a conformational epitope in the N-terminal domain. This domain contains the active site, within a deep gorge, and the peripheral
anionic site at the rim of the gorge. Peripheral-site inhibitors, but not active-site inhibitors, also interfered with adhesion,
and competed with the catalytic monoclonal binding to acetylcholinesterase, indicating that the epitope recognized is associated
with the peripheral anionic site. The inhibitor data also support the supposition that catalysis in these antibodies may have
arisen from stable complexation of acetylcholinesterase with an inhibitor.
We conclude that the catalytic antiacetylcholinesterase antibody interacts with structures associated with the peripheral
anionic site, thus defining a novel site on the molecule involved, in cell adhesion. This finding has implications for our
understanding of the potential importance of this peripheral site in a variety of congenital, neoplastic, and degenerative
conditions. |
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Keywords: | Catalytic antibody acetylcholinesterase cell adhesion peripheral anionic site |
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