Proteolytic processing of amyloid β protein precursor (APP) by thrombin

Search for proteases responsible for an altered processing of APP which generates intermediates containing β A4 peptide is preceding to understand the formation of β amyloid deposits characteristic of Alzheimer's disease, since many studies reveal that APP is ordinarily processed so as not to generate β amyloid. Here, we have examined the action of thrombin, a serine protease in the blood clotting, in APP processing. Thrombin cleaved the mouse recombinant APP 695 in vitro , resulting in the accumulation of 28 kDa fragment. The immunoblot analysis showed that the fragment is derived from the carboxy-terminal side of the recombinant APP 695 . Further, amino acid sequencing exhibited that the fragment is generated by the cleavage at Arg 510 - lle 511 and therefore includes entire β A4 peptide. We consider that the 28 kDa fragment is a possible intermediate for β A4 peptide. Thus thrombin may be involved in the altered processing of APP.