S. Simon et al., The binding sites of inhibitory monoclonal antibodies on acetylcholinesterase - Identification of a novel regulatory site at the putative "back door", J BIOL CHEM, 274(39), 1999, pp. 27740-27746
We investigated the target sites of three inhibitory monoclonal antibodies
on Electrophorus acetylcholinesterase (AChE). Previous studies showed that
Elec-403 and Elec-410 are directed to overlapping but distinct epitopes in
the peripheral site, at the entrance of the catalytic gorge, whereas Elec-4
08 binds to a different region. Using Electrophorus/rat AChE chimeras, we i
dentified surface residues that differed between sensitive and insensitive
AChEs: the replacement of a single Electrophorus residue by its rat homolog
was able to abolish binding and inhibition, for each antibody. Reciprocall
y, binding and inhibition by Elec-403 and by Elec-410 could be conferred to
rat AChE by the reverse mutation. Elec-410 appears to bind to one side of
the active gorge, whereas Elec-403 covers its opening, explaining why the A
ChE-Elec-410 complex reacts faster than the AChE-Elec-403 or AChE-fasciculi
n complexes with two active site inhibitors, m-(N,N,N-trimethyltammonio)tri
fluoro-acetophenone and echothiophate. Elec-408 binds to the region of the
putative "back door," distant from the peripheral site, and does not interf
ere with the access of inhibitors to the active site. The binding of an ant
ibody to this novel regulatory site may inhibit the enzyme by blocking the
back door or by inducing a conformational distortion within the active site
.