Pro-domain removal in ASP-2 and the cleavage of the amyloid precursor are influenced by pH

Background: One of the signatures of Alzheimer's disease is the accumulation of aggregated amyloid protein, A beta, in the brain. A beta arises from cleavage of the Amyloid Precursor protein by beta and gamma secretases, which present attractive candidates for therapeutic targeting. Two beta-secretase candidates, ASP-1 and ASP-2, were identified as aspartic proteases, both of which cleave the amyloid precursor at the beta-site. These are produced as immature transmembrane proteins containing a pro-segment. Results: ASP-2 expressed in HEK293-cells cleaved the Swedish mutant amyloid precursor at different beta-sites at different pHs in vitro. Recent reports show that furin cleaves the pro-peptide of ASP-2, whereas ASP-1 undergoes auto-catalysis. We show that purified recombinant ASP-2 cleaves its own pro-peptide at ph 5 but not pH 8.5 as seen by mass spectrometry, electrophoresis and N-terminal sequencing. Conclusion: We suggest that ASP-2 processing as well as activity are influenced by pH, and hence the cellular localisation of the protein may have profound effects on the production of A beta. These factors should be taken into consideration in the design of potential inhibitors for these enzymes.