Glul1 site cleavage and N-terminally truncated Aβ production upon BACE overexpression

Amyloid beta peptides (Abeta) are generated by the proteolytic processing of the amyloid beta precursor protein (APP). The newly identified beta-site APP-cleaving enzyme (BACE) cleaves APP at Asp1 as well as between Tyr10 and Glul I of Abeta, producing C-terminal fragments (CTFs) C99 and C89, respectively. Subsequent cleavage by gamma-secretase gives rise to Abeta1 -40/42 and Abeta 11 -40/42. Although both full-length and Abeta peptides truncated at residue 11 have been identified in amyloid plaques in the AD brain, the relative proportion of these two cleavage products produced by BACE and secreted into the medium by cultured cells is unknown. Using cell lines stably overexpressing BACE, we found that Abeta 11-40 and Abeta1 1-42 are major Abeta cleavage products generated by BACE. We further showed that BACE utilizes both full-length APP as well as C99 as substrates for the production of C89, and that Abeta 11-40/42 can be generated by sequential cleavage of single APP molecules by BACE and gamma-secretase. Taken together, the abundance of Abeta 1-40/42 produced by BACE suggests that their roles in AD pathogenesis may be underestimated.