Interaction of the collagen-like tail of asymmetric acetylcholinesterase with heparin depends on triple-helical conformation, sequence and stability

The collagen-like tail of asymmetric acetylcholinesterase (AChE) contains t wo heparin-binding domains (HBDs) that interact with heparan sulphate prote oglycans, determining the anchoring of the enzyme at the basal lamina and i ts specific Localization at the neuromuscular junction. Both HBDs are chara cterized by a cluster of basic residues containing a core with the BBXB con sensus sequence (where B represents a basic residue and X a non-basic resid ue). To study the interaction of such HBDs with heparin we have used synthe tic peptides to model the N-terminal and C-terminal sites. CD spectroscopy showed that all peptides are triple-helical at low temperatures, and underg o trimer-to-monomer transitions. Displacement assays of asymmetric AChE bou nd to heparin were performed using the peptides in both monomeric and tripl e-helical states. In the monomeric con- formation, all the peptides were ab le to displace low levels of AChE depending on the basic charge content. In the triplehelical conformation, peptides containing the consensus sequence showed a large increase in the ability to displace bound AChE. Results sug gest that the specific binding of the collagen-like-tail peptides to hepari n depends both on the presence of the core sequence and on the triple-helic al conformation. Moreover, BBXB-containing peptides that are less stable ar e more effective in displacing AChE, suggesting that the interaction region needs a significant amount of structural flexibility to better accommodate the ligand.