Interaction of collagen-like peptide models of asymmetric acetylcholinesterase with glycosaminoglycans: Spectroscopic studies of conformational changes and stability

The effect of heparin on the conformation and stability of triple-helical p eptide models of the collagen tail of asymmetric acetylcholinesterase expan ds our understanding of heparin interactions with proteins and presents an opportunity for clarifying the nature of binding of ligands to collagen tri ple-helix domains. Within the collagen tail of AChE, there are two consensu s sequences for heparin binding of the form BBXB, surrounded by additional basic residues. Circular dichroism studies were used to determine the effec t of the addition of increasing concentrations of heparin on triple-helical peptide models for the heparin binding domains, including peptides in whic h the basic residues within and surrounding the consensus sequence were rep laced by alanine residues. The addition of heparin caused an increased trip le-helix content with saturation properties for the peptide modeling the C- terminal site, while precipitation, with no increased helix content resulte d from heparin addition to the peptide modeling the N-terminal site. The re sults suggest that the two binding sites with a similar triple-helical conf ormation have distinctive ways of interacting with heparin, which must rela te to small differences in the consensus sequence (GRKGR vs GKRGK) and in t he surrounding basic residues. Addition of heparin increased the thermal st ability of all peptides containing the consensus sequence. Heparan sulfate produced conformational and stabilization effects similar to those of hepar in, while chondroitin sulfate led to a cloudy solution, loss of circular di chroism signal, and a smaller increase in thermal stability. Thus, specific ity in both the sequence of the triple helix and the type of glycosaminogly can is required for this interaction.