The organellar peptidasome, PreP: A journey from Arabidopsis to Alzheimer's disease

The novel peptidasome, called presequence protease, PreP, was originally identified and characterized in Arabidopsis thaliana as a mitochondrial matrix and chloroplast stroma localized metalloprotease. PreP has a function as the organellar peptide clearing protease and is responsible for degrading free targeting peptides and also other unstructured peptides up to 65 amino acid residues that might be toxic to organellar functions. PreP contains an inverted Zn-binding motif and belongs to the pitrilysin protease family. The crystal structure of AtPreP refined at 2.1 Å demonstrated a unique totally enclosed large cavity of 10 000 Å3 that opens and closes in response to peptide binding, revealing a novel catalytic mechanism for proteolysis. Homologues of PreP have been found in yeast and human mitochondria. Interestingly, the human PreP, hPreP, is the protease that is responsible for clearing the human brain mitochondria from the toxic amyloid-β peptide (Aβ) associated with Alzheimer's disease (AD). Accumulation of Aβ has been shown in the brain mitochondria from AD patients and mutant transgenic mice overexpressing Aβ. Here, we present a review of our present knowledge on structural and functional characteristics of PreP and discuss its mitochondrial Aβ-degrading activity in the human brain mitochondria in relation to AD.