Cleavage of amyloid precursor protein by an archaeal presenilin homologue PSH

Aberrant cleavage of amyloid precursor protein (APP) by gamma-secretase contributes to the development of Alzheimer's disease. More than 200 disease-derived mutations have been identified in presenilin (the catalytic subunit of gamma-secretase), making modulation of gamma-secretase activity a potentially attractive therapeutic opportunity. Unfortunately, the technical challenges in dealing with intact gamma-secretase have hindered discovery of modulators and demand a convenient substitute approach. Here we report that, similar to gamma-secretase, the archaeal presenilin homolog PSH faithfully processes the substrate APP C99 into A beta 42, A beta 40, and A beta 38. The molar ratio of the cleavage products A beta 42 over A beta 40 by PSH is nearly identical to that by gamma-secretase. The proteolytic activity of PSH is specifically suppressed by presenilin-specific inhibitors. Known modulators of gamma-secretase also modulate PSH similarly in terms of the A beta 42/A beta 40 ratio. Structural analysis reveals association of a known gamma-secretase inhibitor with PSH between its two catalytic aspartate residues. These findings identify PSH as a surrogate protease for the screening of agents that may regulate the protease activity and the cleavage preference of gamma-secretase.