3o65
From Proteopedia
Crystal structure of a Josephin-ubiquitin complex: Evolutionary restraints on ataxin-3 deubiquitinating activity
Structural highlights
Function[ATX3L_HUMAN] Deubiquitinating enzyme that cleaves both 'Lys-48'-linked and 'Lys-63'-linked poly-ubiquitin chains (in vitro). [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] Publication Abstract from PubMedThe Josephin domain is a conserved cysteine protease domain found in four human deubiquitinating enzymes: ataxin-3, the ataxin-3-like protein (ATXN3L), Josephin-1, and Josephin-2. Josephin domains from these four proteins were purified and assayed for their ability to cleave ubiquitin substrates. Reaction rates differed markedly both among the different proteins and for different substrates with a given protein. The ATXN3L Josephin domain is a significantly more efficient enzyme than the ataxin-3 domain despite their sharing 85% sequence identity. To understand the structural basis of this difference, the 2.6 A x-ray crystal structure of the ATXN3L Josephin domain in complex with ubiquitin was determined. Although ataxin-3 and ATXN3L adopt similar folds, they bind ubiquitin in different, overlapping sites. Mutations were made in ataxin-3 at selected positions, introducing the corresponding ATXN3L residue. Only three such mutations are sufficient to increase the catalytic activity of the ataxin-3 domain to levels comparable with that of ATXN3L, suggesting that ataxin-3 has been subject to evolutionary restraints that keep its deubiquitinating activity in check. Crystal Structure of a Josephin-Ubiquitin Complex: EVOLUTIONARY RESTRAINTS ON ATAXIN-3 DEUBIQUITINATING ACTIVITY.,Weeks SD, Grasty KC, Hernandez-Cuebas L, Loll PJ J Biol Chem. 2011 Feb 11;286(6):4555-65. Epub 2010 Nov 30. PMID:21118805[3] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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