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  • 1
    Keywords: brain ; ENVIRONMENT ; CELLS ; IN-VITRO ; CELL ; human ; IN-VIVO ; MICROSCOPY ; MODEL ; VITRO ; VIVO ; NETWORKS ; PROTEIN ; PROTEINS ; TISSUE ; murine ; REDUCTION ; RAT ; SKIN ; IDENTIFICATION ; MUTATION ; FIBER ; MUTATIONS ; LENGTH ; intermediate filaments ; INTERMEDIATE-FILAMENTS ; keratin ; vimentin ; LIVING CELLS ; ATOMIC-FORCE MICROSCOPY ; BEHAVIOR ; INSIGHTS ; intermediate filament ; SINGLE ; RECOMBINANT ; PROTOCOL ; DESMIN ; SWITZERLAND ; LEVEL ; INTERMEDIATE ; PERSISTENCE ; function ; AFM ; ALPHA-KERATIN FIBERS ; HAGFISH SLIME THREADS ; MECHANICAL-BEHAVIOR ; neurofilament ; stretching ; EUKARYOTIC CELLS ; NEUROFILAMENTS
    Abstract: Intermediate filaments (IFs) are structural elements of eukaryotic cells with distinct mechanical properties. Tissue integrity is severely impaired, in particular in skin and muscle, when IFs are either absent or malfunctioning due to mutations. Our knowledge on the mechanical properties of IFs is mainly based on tensile testing of macroscopic fibers and on the rheology of IF networks. At the single filament level, the only piece of data available is a measure of the persistence length of vimentin IFs. Here, we have employed an atomic force microscopy (AFM) based protocol to directly probe the mechanical properties of single cytoplasmic IFs when adsorbed to a solid support in physiological buffer environment. Three IF types were studied in vitro: recombinant murine desmin, recombinant human keratin K5/K14 and neurofilaments isolated from rat brains, which are composed of the neurofilament triplet proteins NF-L, NF-M and NF-H. Depending on the experimental conditions, the AFM tip was used to laterally displace or to stretch single IFs on the support they had been adsorbed to. Upon applying force, IFs were stretched on average 2.6-fold. The maximum stretching that we encountered was 3.6-fold. A large reduction of the apparent filament diameter was observed concomitantly. The observed mechanical properties therefore suggest that IFs may indeed function as mechanical shock absorbers in vivo.
    Type of Publication: Journal article published
    PubMed ID: 16257415
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  • 2
    Keywords: IN-VITRO ; Germany ; MICROSCOPY ; DISEASE ; PROTEIN ; PROTEINS ; DYNAMICS ; BIOLOGY ; fibroblasts ; DAMAGE ; LENGTH ; vimentin ; ATOMIC-FORCE MICROSCOPY ; SMOOTH-MUSCLE ; electron microscopy ; molecular biology ; DEPENDENCE ; DESMIN ; desmin and vimentin intermediate filament ; ELASTIC LIGHT-SCATTERING ; F-ACTIN SOLUTIONS ; MICRORHEOLOGY ; persistence length ; rheology ; strain stiffening ; THERMAL FLUCTUATIONS
    Abstract: We have investigated the viscoelastic properties of the cytoplasmic intermediate filament (IF) proteins desmin and vimentin. Mechanical measurements were supported by time-dependent electron microscopy studies of the assembly process under similar conditions. Network formation starts within 2 min, but it takes more than 30 min until equilibrium mechanical network strength is reached. Filament bundling is more pronounced for desmin than for vimentin. Desmin filaments (persistence length l(p) approximate to 900 nm) are stiffer than vimentin filaments (l(p) approximate to 400 nm), but both IFs are much more flexible than microfilaments. e concentration dependence of the plateau modulus G(0) similar to c(alpha) is much weaker than predicted theoretically for networks of semiflexible filaments. This is more pronounced for vimentin (alpha = 0.47) than for desmin (alpha = 0.70). Both networks exhibit strain stiffening at large shear deformations. At the transition from linear to nonlinear viscoelastic response, only desmin shows characteristics of nonaffine network deformation. Strain stiffening and the maximum modulus occur at strain amplitudes about an order of magnitude larger than those for microfilaments. This is probably attributable to axial slippage within the tetramer building blocks of the IFs. Network deformation beyond a critical strain gamma(max) results in irreversible damage. Strain stiffening sets in at lower concentrations, is more pronounced, and is less sensitive to ionic strength for desmin than for vimentin. Hence, desmin exhibits strain stiffening even at low-salt concentrations, which is not observed for vimentin, and we conclude that the strength of electrostatic repulsion compared to the strength of attractive interactions forming the network junctions is significantly weaker for desmin than for vimentin filaments. These findings indicate that both IFs exhibit distinct mechanical properties that are adapted to their respective cellular surroundings [i.e., myocytes (desmin) and fibroblasts (vimentin)]. (C) 2009 Elsevier Ltd. All rights reserved
    Type of Publication: Journal article published
    PubMed ID: 19281820
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  • 3
    Abstract: Unequal homologous recombination between repetitive genetic elements is one mechanism that mediates genome instability. We have characterized a homologous recombination event between two neighboring LINE-1 sequences in the human gene encoding the beta subunit of phosphorylase kinase (PHKB). It has lead to the deletion of 7574 nucleotides of genomic DNA including exon 8 of this gene, giving rise to glycogen storage disease through phosphorylase kinase deficiency. To our knowledge, this is the first example of a mutation due to unequal homologous recombination between LINE-1 elements. The sequence features of the recombining LINE-1 elements and of the recombination junction site, and possible reasons for the more frequent occurrence of unequal homologous recombination between Alu elements are discussed.
    Type of Publication: Journal article published
    PubMed ID: 9533876
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  • 4
    Keywords: CELLS ; IN-VITRO ; CELL ; VITRO ; NETWORK ; NETWORKS ; PROTEIN ; PROTEINS ; MECHANISM ; DOMAIN ; BIOLOGY ; VARIANTS ; ACID ; STRESS ; LENGTH ; cytoskeleton ; vimentin ; AMINO-ACIDS ; ATOMIC-FORCE MICROSCOPY ; BEHAVIOR ; DOMAINS ; ORIGIN ; VARIANT ; SCIENCE ; F-ACTIN ; PERSISTENCE ; ELASTICITY ; amino acids ; VISCOELASTIC PROPERTIES ; rheology ; BIOPOLYMER NETWORKS ; ACTIN SOLUTIONS ; cell mechanics ; DEFICIENT CELLS ; FLUORESCENT INDICATOR MAG-INDO-1
    Abstract: Intermediate filament networks in the cytoplasm and nucleus are critical for the mechanical integrity of metazoan cells. However, the mechanism of crosslinking in these networks and the origins of their mechanical properties are not understood. Here, we study the elastic behavior of in vitro networks of the intermediate filament protein vimentin. Rheological experiments reveal that vimentin networks stiffen with increasing concentrations of Ca2+ and Mg2+, showing that divalent cations act as crosslinkers. We quantitatively describe the elastic response of vimentin networks over five decades of applied stress using a theory that treats the divalent cations as crosslinkers: at low stress, the behavior is entropic in origin, and increasing stress pulls out thermal fluctuations from single filaments, giving rise to a nonlinear response; at high stress, enthalpic stretching of individual filaments significantly modifies the nonlinearity. We investigate the elastic properties of networks formed by a series of protein variants with stepwise tail truncations and find that the last 11 amino acids of the C-terminal tail domain mediate crosslinking by divalent ions. We determined the single-filament persistence length, l(P) approximate to 0.5 mu m, and Young's modulus, Y approximate to 9 MPa; both are consistent with literature values. Our results provide insight into a crosslinking mechanism for vimentin networks and suggest that divalent ions may help regulate the cytoskeletal structure and mechanical properties of cells. (C) 2010 Elsevier Ltd. All rights reserved
    Type of Publication: Journal article published
    PubMed ID: 20447406
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  • 5
    Abstract: Inherited mutations in the gene coding for the intermediate filament protein desmin have been demonstrated to cause severe skeletal and cardiac myopathies. Unexpectedly, some of the mutated desmins, in particular those carrying single amino acid alterations in the non-alpha-helical carboxy-terminal domain ("tail"), have been demonstrated to form apparently normal filaments both in vitro and in transfected cells. Thus, it is not clear if filament properties are affected by these mutations at all. For this reason, we performed oscillatory shear experiments with six different desmin "tail" mutants in order to characterize the mesh size of filament networks and their strain stiffening properties. Moreover, we have carried out high-frequency oscillatory squeeze flow measurements to determine the bending stiffness of the respective filaments, characterized by the persistence length l(p). Interestingly, mesh size was not altered for the mutant filament networks, except for the mutant DesR454W, which apparently did not form proper filament networks. Also, the values for bending stiffness were in the same range for both the "tail" mutants (l(p)=1.0-2.0 microm) and the wild-type desmin (l(p)=1.1+/-0.5 microm). However, most investigated desmin mutants exhibited a distinct reduction in strain stiffening compared to wild-type desmin and promoted nonaffine network deformation. Therefore, we conclude that the mutated amino acids affect intrafilamentous architecture and colloidal interactions along the filament in such a way that the response to applied strain is significantly altered. In order to explore the importance of the "tail" domain as such for filament network properties, we employed a "tail"-truncated desmin. Under standard conditions, it formed extended regular filaments, but failed to generate strain stiffening. Hence, these data strongly indicate that the "tail" domain is responsible for attractive filament-filament interactions. Moreover, these types of interactions may also be relevant to the network properties of the desmin cytoskeleton in patient muscle.
    Type of Publication: Journal article published
    PubMed ID: 20171226
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  • 6
    Abstract: Cotranslational protein folding can generate pulling forces on the nascent chain that can affect the instantaneous translation rate and thereby possibly feed back on the folding process. Such feedback would represent a new way of coupling translation and folding, different from coupling based on, for example, codon usage. However, to date, we have carried out the experiments used to measure pulling forces generated by cotranslational protein folding either in reconstituted in vitro translation systems lacking chaperones, in ill-defined cell lysates, or in vivo; hence, the effects of chaperones on force generation by folding are unknown. Here, we have studied the cotranslational folding of dihydrofolate reductase (DHFR) in the absence and in the presence of the chaperones trigger factor (TF) and GroEL/ES. DHFR was tethered to the ribosome via a C-terminal linker of varying length, ending with the SecM translational arrest peptide that serves as an intrinsic force sensor reporting on the force generated on the nascent chain when DHFR folds. We find that DHFR folds into its native structure only when it has emerged fully outside the ribosome and that TF and GroEL alone substantially reduces the force generated on the nascent chain by the folding of DHFR, while GroEL/ES has no effect. TF therefore weakens the possible coupling between cotranslational folding and translation.
    Type of Publication: Journal article published
    PubMed ID: 26906929
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  • 7
    Abstract: Deletion of Phe508 in the nucleotide binding domain (F508-NBD1) of the cystic fibrosis transmembrane regulator (CFTR; a cyclic AMP-regulated chloride channel) is the most frequent mutation associated with cystic fibrosis. This mutation affects the maturation and gating of CFTR protein. The search for new high-affinity ligands of CFTR acting as dual modulators (correctors/activators) presents a major challenge in the pharmacology of cystic fibrosis. Snake venoms are a rich source of natural multifunctional proteins, potential binders of ion channels. In this study, we identified the CB subunit of crotoxin from Crotalus durissus terrificus as a new ligand and allosteric modulator of CFTR. We showed that CB interacts with NBD1 of both wild type and F508CFTR and increases their chloride channel currents. The potentiating effect of CB on CFTR activity was demonstrated using electrophysiological techniques in Xenopus laevis oocytes, in CFTR-HeLa cells, and ex vivo in mouse colon tissue. The correcting effect of CB was shown by functional rescue of CFTR activity after 24-h DeltaF508CFTR treatments with CB. Moreover, the presence of fully glycosylated CFTR was observed. Molecular docking allowed us to propose a model of the complex involving of the ABCbeta and F1-like ATP-binding subdomains of DeltaF508-NBD1. Hydrogen-deuterium exchange analysis confirmed stabilization in these regions, also showing allosteric stabilization in two other distal regions. Surface plasmon resonance competition studies showed that CB disrupts the F508CFTR-cytokeratin 8 complex, allowing for the escape of F508CFTR from degradation. Therefore CB, as a dual modulator of DeltaF508CFTR, constitutes a template for the development of new anti-CF agents.
    Type of Publication: Journal article published
    PubMed ID: 27241308
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  • 8
    Abstract: Escherichia coli ClpB and Saccharomyces cerevisiae Hsp104 are members of the Hsp100 family of ring-forming hexameric AAA+ chaperones which promote solubilisation of aggregated proteins and propagation of prions. ClpB and Hsp104 cooperate with cognate Hsp70 chaperones for substrate targeting and activation of ATPase and substrate threading, achieved by transient Hsp70 binding to the repressing ClpB/Hsp104 M-domain. Fundamental differences in ATPase regulation and disaggregation mechanisms have been reported however, raising doubts regarding the working principle of this AAA+ chaperone. In particular unique functional plasticity was suggested to specifically enable Hsp104 to circumvent Hsp70 requirement for derepression in protein disaggregation and prion propagation. We show here that for both ClpB and Hsp104 cooperation with Hsp70 is crucial for efficient protein disaggregation and, in contrast to earlier claims, cannot be circumvented by activating M-domain mutations. Activation of ClpB and Hsp104 requires two signals, relief of M-domain repression and substrate binding, leading to increased ATPase subunit coupling. These data demonstrate that ClpB and Hsp104 operate by the same basic mechanism, underscore a dominant function of Hsp70 in regulating ClpB/Hsp104 activity, and explain a plethora of in vivo studies showing a crucial function of Hsp70 in proteostasis and prion propagation.
    Type of Publication: Journal article published
    PubMed ID: 27616763
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  • 9
    Keywords: ACID, analytical ultracentrifugation, assembly, COMPLEX, COMPLEXES, CYTOARCHITECTURE, cytoskeleton,
    Abstract: It has been documented that mutations in the human desmin gene lead to a severe type of myofibrillar myopathy, termed more specifically desminopathy, which affects cardiac and skeletal as well as smooth muscle. We showed recently that 14 recombinant versions of these disease-causing desmin variants, all involving single amino acid substitutions in the alpha-helical rod domain, interfere with in vitro filament formation at distinct stages of the assembly process. We now provide mechanistic details of how these mutations affect the filament assembly process by employing analytical ultracentrifugation, time-lapse electron microscopy of negatively stained and glycerol-sprayed/low-angle rotary metal-shadowed samples, quantitative scanning transmission electron microscopy, and viscometric studies. In particular, the soluble assembly intermediates of two of the mutated proteins exhibit unusually high s-values, compatible with octamers and other higher-order complexes. Moreover, several of the six filament-forming mutant variants deviated considerably from wild-type desmin with respect to their filament diameters and mass-per-length values. In the heteropolymeric situation with wild-type desmin, four of the mutant variants caused a pronounced "hyper-assembly", when assayed by viscometry. This indicates that the various mutations may cause abortion of filament formation by the mutant protein at distinct stages, and that some of them interfere severely with the assembly of wild-type desmin. Taken together, our findings provide novel insights into the basic intermediate filament assembly mechanisms and offer clues as to how amino acid changes within the desmin rod domain may interfere with the normal structural organization of the muscle cytoskeleton, eventually leading to desminopathy. (c) 2006 Elsevier Ltd. All rights reserved
    Type of Publication: Journal article published
    PubMed ID: 16828798
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  • 10
    Keywords: RECEPTOR ; CELLS ; EXPRESSION ; CELL ; Germany ; human ; PATHWAY ; SYSTEM ; GENE ; GENES ; PROTEIN ; LINES ; ACTIVATION ; MARKER ; T cell ; T cell activation ; T cells ; T-CELL ; T-CELLS ; BINDING ; CELL-LINES ; SIGNAL ; virus ; IDENTIFICATION ; NUMBER ; CELL-LINE ; LINE ; HUMAN-IMMUNODEFICIENCY-VIRUS ; representational difference analysis ; GENE-PRODUCT ; SUBSET ; PRODUCTS ; HIV ; IMMUNODEFICIENCY VIRUS ; NUCLEOCYTOPLASMIC TRANSPORT ; TAP ; 60S RIBOSOMAL-SUBUNITS ; CD83 ; CRM1 ; IMMUNODEFICIENCY-VIRUS REV ; LEPTOMYCIN B ; RAN ; RECEPTOR CRM1 ; RNA export
    Abstract: In metazoans, the nuclear export of bulk mRNAs is mediated by the export receptor TAP, together with its binding partner p15. A number of viral mRNAs, including the unspliced and partially spliced mRNA species of the human immunodeficiency virus (HIV), however, use an alternative export route via the importin beta-related export receptor CRM1. This raises the question of whether a subset of cellular mRNAs might be exported by CRM1 as well. To identify such mRNAs, we performed a systematic screen in different cell lines, using representational difference analyses of cDNA (cDNA-RDA). In HeLa and Cl-4 cells no cellular transcripts could be identified as exported via CRM1. In contrast, we found a number of CRM1-dependent mRNAs in Jurkat T cells, most of which are induced during a T cell response. One of the identified gene products, the dendritic cell marker CD83, was analyzed in detail. CD83 expression depends on a functional CRM1 pathway in activated Jurkat T cells as well as in a heterologous expression system, independent of activation. Our results point to an important role of the CRM1-dependent export pathway for the expression of CD83 and other genes under conditions of T cell activation. (c) 2006 Elsevier Ltd. All rights reserved
    Type of Publication: Journal article published
    PubMed ID: 16580684
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