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The structure of the complex between Rpn13 and K48-diUbThe structure of the complex between Rpn13 and K48-diUb
Structural highlights
Function[UBB_HUMAN] Ubiquitin exists either covalently attached to another protein, or free (unanchored). When covalently bound, it is conjugated to target proteins via an isopeptide bond either as a monomer (monoubiquitin), a polymer linked via different Lys residues of the ubiquitin (polyubiquitin chains) or a linear polymer linked via the initiator Met of the ubiquitin (linear polyubiquitin chains). Polyubiquitin chains, when attached to a target protein, have different functions depending on the Lys residue of the ubiquitin that is linked: Lys-6-linked may be involved in DNA repair; Lys-11-linked is involved in ERAD (endoplasmic reticulum-associated degradation) and in cell-cycle regulation; Lys-29-linked is involved in lysosomal degradation; Lys-33-linked is involved in kinase modification; Lys-48-linked is involved in protein degradation via the proteasome; Lys-63-linked is involved in endocytosis, DNA-damage responses as well as in signaling processes leading to activation of the transcription factor NF-kappa-B. Linear polymer chains formed via attachment by the initiator Met lead to cell signaling. Ubiquitin is usually conjugated to Lys residues of target proteins, however, in rare cases, conjugation to Cys or Ser residues has been observed. When polyubiquitin is free (unanchored-polyubiquitin), it also has distinct roles, such as in activation of protein kinases, and in signaling.[1] [2] [ADRM1_HUMAN] Functions as a proteasomal ubiquitin receptor. Recruits the deubiquitinating enzyme UCHL5 at the 26S proteasome and promotes its activity.[3] [4] [5] [6] [7] Publication Abstract from PubMedThe interaction between K48-linked ubiquitin (Ub) chain and Rpn13 is important for proteasomal degradation of ubiquitinated substrate proteins. Only the complex structure between the N-terminal domain of Rpn13 (Rpn13(NTD)) and Ub monomer has been characterized, while it remains unclear how Rpn13 specifically recognizes K48-linked Ub chain. Using single-molecule FRET, here we show that K48-linked diubiquitin (K48-diUb) fluctuates among distinct conformational states, and a preexisting compact state is selectively enriched by Rpn13(NTD). The same binding mode is observed for full-length Rpn13 and longer K48-linked Ub chain. Using solution NMR spectroscopy, we have determined the complex structure between Rpn13(NTD) and K48-diUb. In this structure, Rpn13(NTD) simultaneously interacts with proximal and distal Ub subunits of K48-diUb that remain associated in the complex, thus corroborating smFRET findings. The proximal Ub interacts with Rpn13(NTD) similarly as the Ub monomer in the known Rpn13(NTD):Ub structure, while the distal Ub binds to a largely electrostatic surface of Rpn13(NTD). Thus, a charge-reversal mutation in Rpn13(NTD) weakens the interaction between Rpn13 and K48-linked Ub chain, causing accumulation of ubiquitinated proteins. Moreover, physical blockage of the access of the distal Ub to Rpn13(NTD) with a proximity-attached Ub monomer can disrupt the interaction between Rpn13 and K48-diUb. Taken together, the bivalent interaction of K48-linked Ub chain with Rpn13 provides the structural basis for Rpn13 linkage selectivity, which opens a new window for modulating proteasomal function. Structural basis for the recognition of K48-linked Ub chain by proteasomal receptor Rpn13.,Liu Z, Dong X, Yi HW, Yang J, Gong Z, Wang Y, Liu K, Zhang WP, Tang C Cell Discov. 2019 Apr 2;5:19. doi: 10.1038/s41421-019-0089-7. eCollection 2019. PMID:30962947[8] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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