Understanding K11‐ polyubiquitin recognition at the 26S Proteasome

Abstract

Ubiquitination, the covalent attachment of ubiquitin to target proteins, is a reversible post‐translational modification that regulates many important cellular processes. Ubiquitin chains linked at Lys48 (K48) serve as a signal for proteasomal degradation; whereas K63‐linked chains have non‐proteolytic function. Lysine 11 (K11)‐linked chains are upregulated when the human E3 anaphase‐promoting complex (APC/C) is activated during mitosis, which initiates substrate degradation by attaching K11‐linked chains for proteasomal targeting. However, why cells use K11‐linked chains instead of K48 for this purpose and how the chains are recognized by the shuttle factors and receptors on the proteasome are not known. At the proteasome it has been well established that there are two ubiquitin receptors that preferentially bind K48‐linked chains, RPN10 and RPN13. We are investigating the role of hRpn13 conserved pleckstrin‐like receptor domain (Pru) and the hRpn10 ubiquitin interacting motifs (UIM) in binding to K11‐linked di‐ubiquitin. We show that K11‐linked di‐ubiquitin binds Rpn13Pru domain with similar affinity as K48 and K63‐linked di‐ubiquitin. These interactions may play an important role in cell cycle regulation by serving as the recognition site for proteolytic degradation and implies that the proteasome may use other ubiquitin binding domains to discriminate between different chain types.