Proteolytic processing of human amyloid β protein precursor in insect cells: Major carboxyl-terminal fragment is identical to its human counterpart

The predominant component of amyloid plaques of Alzheimer's disease is the amyloid β protein (Aβ), a 39-42-amino-acid peptide derived by proteolysis of a family of precursors known as amyloid precursor proteins (APP). In mammalian brain and in cultured mammalian cells, the release of APP amino-terminal fragments into the extracellular medium occurs by a proteolytic cleavage within the Aβ domain, thereby precluding amyloidogenesis. Infection of Sf9 insect cells with baculovirus vectors containing APP cDNAs results in high levels of APP expression. The concomitant release of amino-terminal fragments of APP and the production of carboxyl-terminal, cell-associated cleavage products are observed. Here we demonstrate by direct protein microsequencing that the proteolytic processing of APP in the Sf9 cells generates a prominent carboxyl-terminal species that is identical to that produced in human cells, suggesting that the major pathway for proteolytic processing of APP is conserved among metazoans.