6ven
Yeast COMPASS in complex with a ubiquitinated nucleosome
Structural highlights
FunctionUBC_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 PubMedMethylation of histone H3K4 is a hallmark of actively transcribed genes that depends on mono-ubiquitination of histone H2B (H2B-Ub). H3K4 methylation in yeast is catalyzed by Set1, the methyltransferase subunit of COMPASS. We report here the cryo-EM structure of a six-protein core COMPASS subcomplex, which can methylate H3K4 and be stimulated by H2B-Ub, bound to a ubiquitinated nucleosome. Our structure shows that COMPASS spans the face of the nucleosome, recognizing ubiquitin on one face of the nucleosome and methylating H3 on the opposing face. As compared to the structure of the isolated core complex, Set1 undergoes multiple structural rearrangements to cement interactions with the nucleosome and with ubiquitin. The critical Set1 RxxxRR motif adopts a helix that mediates bridging contacts between the nucleosome, ubiquitin and COMPASS. The structure provides a framework for understanding mechanisms of trans-histone cross-talk and the dynamic role of H2B ubiquitination in stimulating histone methylation. Structural basis for COMPASS recognition of an H2B-ubiquitinated nucleosome.,Worden EJ, Zhang X, Wolberger C Elife. 2020 Jan 10;9. pii: 53199. doi: 10.7554/eLife.53199. PMID:31922488[3] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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