The cell adhesion and neurite outgrowth-promoting function of acetylcholinesterase has been localised to the area of the peripheral anionic site. In order to precisely determine the site involved, we used synthetic peptides representing sequences of the peripheral anionic site and its surrounds, and investigated their binding to a panel of monoclonal antibodies that inhibit cell adhesion/neurite outgrowth and/or to recognise the peripheral anionic site. Binding to laminin-1 and collagen IV was also investigated. A relationship between recognition of the sequence 37-50, representing a surface loop adjacent to the peripheral anionic site, and the degree of inhibition of cell adhesion was observed; both laminin-1 and collagen IV also bound this loop with high affinity. Neurite outgrowth on coverslips coated with this peptide was similar to those coated with acetylcholinesterase itself. Adhesion-inhibiting antibodies also recognised the omega loop 69-96, as did laminin-1 and collagen IV. Laminin also bound the sequences 55-66 and 340-353, recognised by the antibodies to varying degrees, but collagen did not. All these peptides were able to promote neurite outgrowth to some degree. No binding to the amyloid-binding omega loop 275-304 by the ligands was observed, nor did the antibodies recognise this consistently. No relationship was observed between the degree of inhibition of acetylcholinesterase and inhibition of neurite outgrowth by the antibodies from which we conclude that the neurite outgrowth function is non-cholinergic. In conclusion, we have identified a specific conformational structure on acetylcholinesterase, comprising adjacent surface loops between residues 37-50 and 69-96, with additional involvement of the sequences 55-66 and 340-353, that mediates cell adhesion and neurite outgrowth. (C) Elsevier Inc. All rights reserved.