Figure 1. Mutant ubiquitin (UBB+1) reduces Aβ plaques in APPPS1 mice. (A) Schematic diagram of amyloid precursor protein (APP) processing leading to Aβ. (B) γ-secretase is a multimeric enzyme complex that cleaves APP C-terminal fragment (CTF) to produce Aβ and an APP intracellular domain (AICD). (C) Transgenic APPPS1 mice carry two mutations that represent early-onset AD and develop age-related amyloid plaque pathology. (D) In APPPS1xUBB+1 mice, APP CTF-β levels are reduced and γ-secretase function is partially restored. (E) Besides secretases, alternate protein degradation pathways have been reported to degrade APP and Aβ.