PINK1 and Parkinson disease: Recently, a series of studies involving the PD proteins parkin (an E3 ubiquitin ligase) and PINK1 (a serine/threonine kinase with a mitochondrial targeting sequence), mutations in which are the most common cause of recessive PD [10], [16] have highlighted a potential role for both proteins in the clearance of mitochondria from cells via autophagy—a process known as mitophagy [17].