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    Keywords: PEPTIDE ; CELLS ; IN-VITRO ; CELL ; human ; VITRO ; PROTEIN ; DOMAIN ; BIOLOGY ; SPECTROSCOPY ; FORM ; SUBUNIT ; MUTATION ; CRYSTAL-STRUCTURE ; STABILITY ; INTERMEDIATE-FILAMENTS ; vimentin ; DIMER ; lamin ; DOMAINS ; ATOMIC-STRUCTURE ; intermediate filament ; SINGLE ; molecular biology ; assembly ; REARRANGEMENT ; coiled coil ; COILED-COIL ; nuclear lamins ; TEMPERATURE ; AMINO-ACID SUBSTITUTIONS ; circular dichroism ; POSITION ; STATE ; biophysical analysis ; CONSENSUS MOTIF ; GCN4 LEUCINE-ZIPPER ; HYDROPHOBIC CORE ; Oligomerisation ; OLIGOMERIZATION STATE ; PROTEIN STRUCTURES
    Abstract: Interestingly, our previously published structure of the coil 1A fragment of the human intermediate filament protein vimentin turned out to be a monomeric alpha-helical coil instead of the expected dimeric coiled coil. However, the 39-amino-acid-long helix had an intrinsic curvature compatible with a coiled coil. We have now designed four mutants of vimentin coil 1A, modifying key a and d positions in the heptad repeat pattern, with the aim of investigating the molecular criteria that are needed to stabilize a dimeric coiled-coil structure. We have analysed the biophysical properties of the mutants by circular dichroism spectroscopy, analytical ultracentrifugation and X-ray crystallography. All four mutants exhibited an increased stability over the wild type as indicated by a rise in the melting temperature (T-m). At a concentration of 0.1 mg/ml, the T-m of the peptide with the single point mutation Y117L increased dramatically by 46 degrees C compared with the wild-type peptide. In general, the introduction of a single stabilizing point mutation at an a or a d position did induce the formation of a stable dimer as demonstrated by sedimentation equilibrium experiments. The dimeric oligomerisation state of the Y117L peptide was furthermore confirmed by Xray crystallography, which yielded a structure with a genuine coiled-coil geometry. Most notably, when this mutation was introduced into full-length vimentin, filament assembly was completely arrested at the unit-length filament (ULF) level, both in vitro and in cDNA-transfected cultured cells. Therefore, the low propensity of the wild-type coil 1A to form a stable two-stranded coiled coil is most likely a prerequisite for the end-to-end annealing of ULFs into filaments. Accordingly, the coil 1A domains might "switch" from a dimeric alpha-helical coiled coil into a more open structure, thus mediating, within the ULFs, the conformational rearrangements of the tetrameric subunits that are needed for the intermediate filament elongation reaction. (C) 2009 Elsevier Ltd. All rights reserved
    Type of Publication: Journal article published
    PubMed ID: 19422834
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  • 2
    Keywords: CELLS ; CELL ; CELL-PROLIFERATION ; Germany ; GENERATION ; DISTINCT ; PROTEIN ; PROTEINS ; COMPONENTS ; MONOCLONAL-ANTIBODY ; BIOLOGY ; antibodies ; antibody ; PARTICLES ; IDENTIFICATION ; SPECTROMETRY ; REGION ; REGIONS ; XENOPUS ; MONOCLONAL-ANTIBODIES ; DNA-REPLICATION ; REPLICATION ; CLUSTER ; XENOPUS-LAEVIS ; WERNER-SYNDROME PROTEIN ; AMPLIFIED NUCLEOLI ; DESMOSOMAL PLAQUE ; NUCLEAR LAMINA PROTEINS ; NUCLEOPLASMIN FAMILY ; RIBOSOME BIOGENESIS
    Abstract: It has recently become clear that the nucleolus, the most prominent nuclear subcompartment, harbors diverse functions beyond its classic role in ribosome biogenesis. To gain insight into nucleolar functions, we have purified amplified nucleoli from Xenopus laevis oocytes using a novel approach involving fluorescence-activated cell sorting techniques. The resulting protein fraction was analyzed by mass spectrometry and used for the generation of monoclonal antibodies directed against nucleolar components. Here, we report the identification and molecular characterization of a novel, ubiquitous protein, which in most cell types appears to be a constitutive nucleolar component. Immunolocalization studies have revealed that this protein, termed NO66, is highly conserved during evolution and shows in most cells analyzed a dual localization pattern, i.e., a strong enrichment in the granular part of nucleoli and in distinct nucleoplasmic entities. Colocalizations with proteins Ki-67, HP1alpha, and PCNA, respectively, have further shown that the staining pattern of NO66 overlaps with certain clusters of late replicating chromatin. Biochemical experiments have revealed that protein NO66 cofractionates with large preribosomal particles but is absent from cytoplasmic ribosomes. We propose that in addition to its role in ribosome biogenesis protein NO66 has functions in the replication or remodeling of certain heterochromatic regions
    Type of Publication: Journal article published
    PubMed ID: 14742713
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