PRKN and Parkinson disease: The best known of the RBR enzymes are parkin, which has a prominent role in the manifestation of early-onset Parkinson's disease, and HOIP (HOIL-1-interacting protein) and HOIL-1 (haem-oxidized IRP2 ubiquitin ligase 1), both of which are components of the multiprotein LUBAC (linear ubiquitin chain assembly complex).