Human aspartic protease memapsin 2 cleaves the β-secretase site of β-amyloid precursor protein

TLDR

The protease domain of memapsin 2 cDNA was expressed in *E. coli*, purified, and shown to specifically hydrolyze peptides derived from the β‑secretase site of both wild‑type and Swedish mutant β‑amyloid precursor protein, with over 60‑fold increased catalytic efficiency for the mutant.

Abstract

The cDNAs of two new human membrane-associated aspartic proteases, memapsin 1 and memapsin 2, have been cloned and sequenced. The deduced amino acid sequences show that each contains the typical pre , pro , and aspartic protease regions, but each also has a C-terminal extension of over 80 residues, which includes a single transmembrane domain and a C-terminal cytosolic domain. The protease domain of memapsin 2 cDNA was expressed in Escherichia coli and was purified. Recombinant memapsin 2 specifically hydrolyzed peptides derived from the β-secretase site of both the wild-type and Swedish mutant β-amyloid precursor protein (APP) with over 60-fold increase of catalytic efficiency for the latter. Expression of APP and memapsin 2 in HeLa cells showed that memapsin 2 cleaved the β-secretase site of APP intracellularly. These and other results suggest that memapsin 2 fits all of the criteria of β-secretase, which catalyzes the rate-limiting step of the in vivo production of the β-amyloid (Aβ) peptide leading to the progression of Alzheimer's disease. Recombinant memapsin 2 also cleaved a peptide derived from the processing site of presenilin 1, albeit with poor kinetic efficiency. Alignment of cleavage site sequences of peptides indicates that the specificity of memapsin 2 resides mainly at the S 1 ′ subsite, which prefers small side chains such as Ala, Ser, and Asp.