2ru6
The pure alternative state of ubiquitin
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 PubMedWe present the nuclear Overhauser effect-based structure determination of the Q41N variant of ubiquitin at 2500 bar, where the alternatively folded N2 state is 97% populated. This allows us to characterize the structure of the "pure" N2 state of ubiquitin. The N2 state shows a substantial change in the orientation of strand beta5 compared to that of the normal folded N1 state, which matches the changes seen upon binding of ubiquitin to ubiquitin-activating enzyme E1. The recognition of E1 by ubiquitin is therefore best explained by conformational selection rather than induced-fit motion. Close Identity between Alternatively Folded State N2 of Ubiquitin and the Conformation of the Protein Bound to the Ubiquitin-Activating Enzyme.,Kitazawa S, Kameda T, Kumo A, Yagi-Utsumi M, Baxter NJ, Kato K, Williamson MP, Kitahara R Biochemistry. 2014 Jan 28;53(3):447-9. doi: 10.1021/bi401617n. Epub 2014 Jan 10. PMID:24401037[3] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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