Characterization of PARL-Mediated Intramembrane Proteolysis

Abstract

Intramembrane proteolysis is the process by which membrane-embedded proteases cleave substrates that are also embedded within the lipid bilayer or lie near to the bilayer. Rhomboid intramembrane proteases are a ubiquitous superfamily of serine intramembrane proteases that play a role in a wide variety of cellular processes. The mammalian mitochondrial rhomboidprotease, Presenilin-Associated Rhomboid Like (PARL), is a critical regulator of mitochondrial homeostasis through its cleavage of substrates such as PINK1 (Phosphatase and tensin(PTEN)-induced putative kinase 1), PGAM5 (phosphoglycerate mutase family member 5), and Smac (Second mitochondrial-derived activator of caspases), which have roles in mitochondrialquality control and apoptosis.This thesis aims to assess PARL-mediated cleavage of several different substrates using an in vitro FRET-based kinetic assay with recombinantly expressed and purified human PARL (HsPARL). We hypothesize that truncations of PARL identified in vivo will have a regulatory effect on PARL-mediated cleavage and that there will be significant differences in the catalytic parameters obtained for cleavage of each unique substrate by HsPARL. Furthermore, we hypothesize that the lipid cardiolipin, which is specific to the inner mitochondrial membrane where PARL resides, will have an effect on the proteolytic activity of HsPARL. Finally, we aim to assess PARL-mediated cleavage of several Parkinson’s disease-associated variants of PINK1 that harbour a mutation within or near the PARL cleavage site. We hypothesize that these mutations in PINK1 will impair PARL-mediated cleavage and this may provide rationale for the molecular etiology of these mutations in Parkinson’s disease pathogenesis.