The amyloid beta-protein precursor and its mammalian homologues. Evidence for a zinc-modulated heparin-binding superfamily

Abstract

The Alzheimer beta-amyloid precursor protein (APP) contains an ectodomain zinc binding site that has been reported to modulate the heparin affinity and protease-inhibitory properties of the molecule. This motif, GVEFVCCP, is highly conserved in amyloid precursor-like proteins 1 and 2 (APLP1 and APLP2), as well as in the Drosophila and Caenorhabditis elegans APP-like proteins (APPL and APL-1). To determine whether the function of this domain is preserved in the human APP-like proteins, the effect of zinc in modulating the elution profile of these proteins upon heparin-Sepharose chromatography was studied. Both APLP1 and APLP2 bound heparin-Sepharose and had NaCl elution profiles similar to that of APP. As previously reported for APP, zinc increased the recovery of APLP1 and APLP2 upon heparin-Sepharose chromatography. APP, APLP1, and APLP2 all bind zinc-chelating Sepharose, indicating that the zinc binding motif may be functionally conserved in these proteins. Additionally, APP, APLP1, and APLP2 migrate at higher molecular sizes (approximately 40 kDa) on SDS-polyacrylamide gel electrophoresis than their predicted molecular sizes. We report data that compare the physicochemical properties of APP to its novel APLP homologues and indicate that these molecules behave as a family of zinc-modulated, heparin-binding proteins.