1gjz
From Proteopedia
Solution structure of a dimeric N-terminal fragment of human 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] Evolutionary Conservation Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf. Publication Abstract from PubMedPrevious peptide dissection and kinetic experiments have indicated that in vitro folding of ubiquitin may proceed via transient species in which native-like structure has been acquired in the first 45 residues. A peptide fragment, UQ(1-51), encompassing residues 1 to 51 of ubiquitin was produced in order to test whether this portion has propensity for independent self-assembly. Surprisingly, the construct formed a folded symmetrical dimer that was stabilised by 0.8 M sodium sulphate at 298 K (the S state). The solution structure of the UQ(1-51) dimer was determined by multinuclear NMR spectroscopy. Each subunit of UQ(1-51) consists of an N-terminal beta-hairpin followed by an alpha-helix and a final beta-strand, with orientations similar to intact ubiquitin. The dimer is formed by the third beta-strand of one subunit interleaving between the hairpin and third strand of the other to give a six-stranded beta-sheet, with the two alpha-helices sitting on top. The helix-helix and strand portions of the dimer interface also mimic related features in the structure of ubiquitin. The structural specificity of the UQ(1-51) peptide is tuneable: as the concentration of sodium sulphate is decreased, near-native alternative conformations are populated in slow chemical exchange. Magnetization transfer experiments were performed to characterize the various species present in 0.35 M sodium sulphate, namely the S state and two minor forms. Chemical shift differences suggest that one minor form is very similar to the S state, while the other experiences a significant conformational change in the third strand. A segmental rearrangement of the third strand in one subunit of the S state would render the dimer asymmetric, accounting for most of our results. Similar small-scale transitions in proteins are often invoked to explain solvent exchange at backbone amide proton sites that have an intermediate level of protection. Structure and properties of a dimeric N-terminal fragment of human ubiquitin.,Bolton D, Evans PA, Stott K, Broadhurst RW J Mol Biol. 2001 Dec 7;314(4):773-87. PMID:11733996[3] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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