HYDROLYSIS OF AMYLOID PRECURSOR PROTEIN-DERIVED PEPTIDES BY CYSTEINE PROTEINASES AND EXTRACTS OF RAT-BRAIN CLATHRIN-COATED VESICLES

Amyloid precursor proteins (APPs) and C-terminal fragments were colocalized with cysteine proteinase-like enzymes in purified rat brain clathrin-coated vesicles. Vesicular extracts degraded beta A4(12-28), yielding a product profile similar to that of purified rat brain cathepsin B. Cathepsin B degraded this peptide sequentially, with initial cleavage occurring at Val(18)-Phe(19) and Phe(19)-Phe(20) followed by release of dipeptides. Enzyme also hydrolyzed beta A4(1-40) at Phe(19)-Phe(20) bond but at lower rates, likely due to aggregate formation. An octapeptide analogue of the domain adjacent to beta A4 (N-Ac-Val-Lys-Met-Asp-Ala-Glu-Phe-NH2) was also hydrolyzed by brain cathepsins B and L, and metalloendopeptidase 24.11. Enzymes acted at multiple sites, but only 24.1 1 cleaved the Met-Asp bond, thus resembling a proposed beta-secretase. Data imply that clathrin-coated vesicles contain cysteine-like proteinases capable of initiating the processing of APP or its fragments.