IDENTIFICATION OF HEPARIN-BINDING DOMAINS IN THE AMYLOID PRECURSOR PROTEIN OF ALZHEIMERS-DISEASE BY DELETION MUTAGENESIS AND PEPTIDE-MAPPING

Recent studies have shown that the binding of the amyloid protein prec ursor (APP) of Alzheimer's disease to heparan sulfate proteoglycans (H SPGs) can modulate a neurite outgrowth-promoting function associated w ith APP. We used three different approaches to identify heparin-bindin g domains in APP. First, as heparin-binding domains are likely to be w ithin highly folded regions of proteins, we analyzed the secondary str ucture of APP using several predictive algorithms. This analysis showe d that two regions of APP(695) contain a high degree of secondary stru cture, and clusters of basic residues, considered mandatory for hepari n binding, were found principally within these regions. To determine w hich domains of APP bind heparin, deletion mutants of APP(695) were pr epared and analyzed for binding to a heparin affinity column. The resu lts suggested that there must be at least two distinct heparin-binding regions in APP. To identify novel heparin-binding regions, peptides h omologous to candidate heparin-binding domains were analyzed for their ability to bind heparin. These experiments suggested that APP contain s at least four heparin-binding domains. The presence of more than one heparin-binding domain on APP suggests the possibility that APP may i nteract with more than one type of glycosaminoglycan.