A metalloproteinase inhibitor domain in Alzheimer amyloid protein precursor.

Extracellular deposition of amyloid beta-protein (beta-AP), or A4 protein (M(r) 4,000), is associated with Alzheimer's disease and with Down's syndrome (trisomy for chromosome 21). The large membrane-bound precursor protein (APP) of beta-AP is normally cleaved within the beta-AP region by a putative proteinase (APP secretase) to release its extracellular portion; beta-AP is produced by an alternative proteolytic processing. Here we demonstrate that APP contains a proteinase inhibitor domain for the matrix metalloproteinase gelatinase A, which is located in the C-terminal glycosylated region of the secretory forms of APP. In addition, we show that the gelatinase has an APP secretase-like activity, which hydrolyses the Lys16-Leu17 bond in the beta-AP sequence. Our results indicate that the proteinase inhibitor domain of APP and gelatinase A may be involved in the formation of beta-AP.