EXPRESSION, PURIFICATION AND CHARACTERIZATION OF A KUNITZ-TYPE PROTEASE INHIBITOR DOMAIN FROM HUMAN AMYLOID PRECURSOR PROTEIN HOMOLOG

The Kunitz-type protease inhibitor domain from a recently identified h omolog of the Alzheimer amyloid precursor protein (APPH KPI) was expre ssed in yeast, purified and characterized. Its inhibition profile towa rds several serine proteases was studied and compared to that of APP K PI, the Kunitz domain from the Alzheimer amyloid precursor protein. AP PH KPI was shown to inhibit proteases with trypsin-like specificity wi th an inhibitor profile resembling that of the APP KPI domain. The KPI domains from APP and APPH inhibited trypsin (K-i = 0.02 nM), and plas ma kallikrein (K-i = 86 nM) with approximal equal affinity. In compari son to APP KPI (K-i = 82 nM) the KPI domain of the homolog, APPH KPI, (K-i = 8.8 nM) was a more potent inhibitor of glandular kallikrein. AP PH KPI was a less potent inhibitor of chymotrypsin than APP KPI (K-i = 78 nM as compared to K-i = 6 nM), plasmin (K-i = 81 nM as compared to 42 nM), and factor XI, (K-i = 14 nM as compared to K-i = 0.7 nM). The affinity of factor XI(a) for APPH KPI is sufficiently high to allow f or an interaction in the blood. It is, however, well possible that the physiological protease ligand for the receptor-like APPH protein has yet to be identified.