6qml
UCHL3 in complex with synthetic, K27-linked diubiquitin
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 PubMedFunctional analysis of lysine 27-linked ubiquitin chains ((K27)Ub) is difficult due to the inability to make them through enzymatic methods and due to a lack of model tools and substrates. Here we generate a series of ubiquitin (Ub) tools to study how the deubiquitinase UCHL3 responds to (K27)Ub chains in comparison to lysine 63-linked chains and mono-Ub. From a crystal structure of a complex between UCHL3 and synthetic (K27)Ub2, we unexpectedly discover that free (K27)Ub2 and (K27)Ub2-conjugated substrates are natural inhibitors of UCHL3. Using our Ub tools to profile UCHL3's activity, we generate a quantitative kinetic model of the inhibitory mechanism and we find that (K27)Ub2 can inhibit UCHL3 covalently, by binding to its catalytic cysteine, and allosterically, by locking its catalytic loop tightly in place. Based on this inhibition mechanism, we propose that UCHL3 and (K27)Ub chains likely sense and regulate each other in cells. K27-Linked Diubiquitin Inhibits UCHL3 via an Unusual Kinetic Trap.,van Tilburg GBA, Murachelli AG, Fish A, van der Heden van Noort GJ, Ovaa H, Sixma TK Cell Chem Biol. 2021 Feb 18;28(2):191-201.e8. doi:, 10.1016/j.chembiol.2020.11.005. Epub 2020 Nov 24. PMID:33238157[3] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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