DPP4 and type 2 diabetes mellitus: Here, using small-molecule compounds, capillary western analysis of PrP fragmentation (29), and reversed genetics, two type II membrane proteins of the S9B peptidase subfamily were found to perform β-endoproteolysis of PrPC: fibroblast activation protein (FAP; also known as prolyl endopeptidase FAP), which is associated with tissue remodeling (30), and dipeptidyl peptidase-4 (DPP4; also known as CD26), an established drug target in type 2 diabetes (31).