6oq1
Crystal Structure of Branched K11/K48-Linked Tri-Ubiquitin
Structural highlights
FunctionUBB_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] Publication Abstract from PubMedPost-translational substrate modification with ubiquitin is essential for eukaryotic cellular signaling. Polymeric ubiquitin chains are assembled with specific architectures, which convey distinct signaling outcomes depending on the linkages involved. Recently, branched K11/K48-linked polyubiquitins were shown to enhance proteasomal degradation during mitosis. To better understand the underlying structural mechanisms, we determined the crystal and NMR structures of branched K11/K48-linked tri-ubiquitin and discovered a previously unobserved interdomain interface between the distal ubiquitins. Small-angle neutron scattering and site-directed mutagenesis corroborated the presence of this interface, which we hypothesized to be influential in the physiological role of branched K11/K48-linked chains. Yet, experiments probing polyubiquitin interactions-deubiquitination assays, binding to proteasomal shuttle hHR23A-showed negligible differences between branched K11/K48-linked tri-ubiquitin and related di-ubiquitins. However, significantly stronger binding affinity for branched K11/K48-linked tri-ubiquitin was observed with proteasomal subunit Rpn1, thereby suggesting a functional impact of this interdomain interface and pinpointing the mechanistic site of enhanced degradation. Branching via K11 and K48 Bestows Ubiquitin Chains with a Unique Interdomain Interface and Enhanced Affinity for Proteasomal Subunit Rpn1.,Boughton AJ, Krueger S, Fushman D Structure. 2019 Oct 29. pii: S0969-2126(19)30349-1. doi:, 10.1016/j.str.2019.10.008. PMID:31677892[3] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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