The E3 Ubiquitin ligase parkin is recruited to the 26S proteasome via the proteasomal ubiquitin receptor Rpn13 [Molecular Bases of Disease]

February 9th, 2015 by Aguileta, M. A., Korac, J., Durcan, T. M., Trempe, J., Haber, M., Gehring, K., Elsasser, S., Waidmann, O., Fon, E. A., Husnjak, K.

Mutations in the Park2 gene, encoding the RING-HECT hybrid E3 ubiquitin ligase parkin, are responsible for a common familial form of Parkinson′s disease (PD). By mono- and polyubiquitinating target proteins, parkin regulates various cellular processes, including degradation of proteins within the 26S proteasome, a large multimeric degradation machine. In our attempt to further elucidate the function of parkin, we have identified the proteasomal ubiquitin receptor Rpn13/ADRM1 as a parkin-interacting protein. We show that the N-terminal ubiquitin-like (Ubl) domain of parkin binds directly to the pleckstrin-like receptor for ubiquitin (Pru) domain within Rpn13. Using mutational analysis and NMR, we find that Pru binding involves the hydrophobic patch surrounding Ile44 in the parkin Ubl, a region that is highly conserved between ubiquitin and Ubl domains. However, compared to ubiquitin, the parkin Ubl exhibits greater than 10-fold higher affinity for the Pru domain. Moreover, knockdown of Rpn13 in cells increases parkin levels and abrogates parkin recruitment to the 26S proteasome, establishing Rpn13 as the major proteasomal receptor for parkin. In contrast, silencing Rpn13 did not impair parkin recruitment to mitochondria or parkin-mediated mitophagy upon CCCP-induced mitochondrial depolarization. However, it did delay the clearance of mitochondrial proteins (TIM23, TIM44 and TOM20) and enhance parkin autoubiquitination. Taken together, the findings implicate Rpn13 in linking parkin to the 26S proteasome and regulating the clearance of mitochondrial proteins during mitophagy.