2rsu | pdb_00002rsu
Alternative structure of Ubiquitin
Structural highlights
Function[UBC_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 PubMedIt is becoming increasingly clear that proteins transiently populate high-energy excited states as a necessary requirement for function. Here, we demonstrate that rational mutation based on the characteristics of the structure and dynamics of proteins obtained from pressure experiments is a new strategy for amplifying particular fluctuations in proteins. We have previously shown that ubiquitin populates a high-energy conformer, N2, at high pressures. Here, we show that the Q41N mutation favors N2: high-pressure nuclear magnetic resonance (NMR) shows that N2 is approximately 70% populated in Q41N but only approximately 20% populated in the wild type at ambient pressure. This allows us to characterize the structure of N2, in which alpha1-helix, the following loop, beta3-strand, and beta5-strand change their orientations relative to the remaining regions. Conformational fluctuation on the microsecond time scale, characterized by (15)N spin relaxation NMR analysis, is markedly increased for these regions of the mutant. The N2 conformers produced by high pressure and by the Q41N mutation are quite similar in both structure and dynamics. The conformational change to produce N2 is proposed to be a novel dynamic feature beyond the known recognition dynamics of the protein. Indeed, it is orthogonal to that seen when proteins containing a ubiquitin-interacting motif bind at the hydrophobic patch of ubiquitin but matches changes seen on binding to the E2 conjugating enzyme. More generally, structural and dynamic effects of hydrodynamic pressure are shown to be useful for characterizing functionally important intermediates. Solution Structure of the Q41N Variant of Ubiquitin as a Model for the Alternatively Folded N2 State of Ubiquitin.,Kitazawa S, Kameda T, Yagi-Utsumi M, Sugase K, Baxter NJ, Kato K, Williamson MP, Kitahara R Biochemistry. 2013 Mar 19;52(11):1874-85. doi: 10.1021/bi301420m. Epub 2013 Mar, 7. PMID:23421577[3] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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