K48 Linked Ubiquitin Chains Affect Proteasomal Unfolding Ability via Interactions with Rpn10

Abstract

The ubiquitin proteasome system plays a crucial role in homeostasis by preferentially degrading proteins that are damaged, misfolded, or no longer necessary in regulatory processes. Substrates are recognized and polyubiquitinated by E1, E2, and E3 enzymes, which leads to recruitment and degradation by the proteasome. However, the proteasome does not always completely degrade its target and will release a protein fragment if unfolding does not occur. We previously showed that the proteasome’s unfolding ability is dependent on the ubiquitin chains’ interactions with proteasomal ubiquitin receptors, and that different chain architectures (linear K63 chains vs branched K48 and K63‐containing chains) had different receptor dependencies. To investigate the interaction of substrates bearing linear K48‐linked chains, we turned to the E3 ligase Ubr1, which recognizes N‐end rule substrates. A model unfolding ability substrate containing an N‐terminal arginine was degraded by wild‐type and ubiquitin‐receptor mutant proteins. The results indicate that although ubiquitin receptors Rpn1, Rpn10, and Rpn13 are all important for degradation of this substrate, Rpn10 has the greatest effect on the proteasome’s unfolding ability.Support or Funding InformationThis material is based upon work supported by the National Science Foundation under Grant No. 1515229 to DAK.