: Tubulin dimer binding proteins

International audienceMicrotubules play an essential role in eukaryotic cells, where they perform a wide variety of functions. In this paper, we describe the characterization of proteins associated to tubulin dimer in its native form, using affinity chromatography and mass spectrometry. We used an immunoaffinity column with coupled-monoclonal antibody directed against the alpha-tubulin C-terminus. Tubulin was first loaded onto the column, then interphase and mitotic cell lysates were chromatographed. Tubulin-binding proteins were eluted using a peptide mimicking the alpha-tubulin C-terminus. Elution fractions were analyzed by SDS-PAGE, and a total of 14 proteins were identified with high confidence by mass spectrometry. These proteins could be grouped in four classes: known tubulin-binding proteins, one microtubule-associated protein, heat shock proteins, and proteins that were not shown previously to bind tubulin dimer or microtubules

MAP6-F is a temperature sensor that directly binds to and protects microtubules from cold-induced depolymerization.: Microtubule stabilization by MAP6

International audienceMicrotubules are dynamic structures that present the peculiar characteristic to be ice-cold labile in vitro. In vivo, microtubules are protected from ice-cold induced depolymerization by the widely expressed MAP6/STOP family of proteins. However, the mechanism by which MAP6 stabilizes microtubules at 4 °C has not been identified. Moreover, the microtubule cold sensitivity and therefore the needs for microtubule stabilization in the wide range of temperatures between 4 and 37 °C are unknown. This is of importance as body temperatures of animals can drop during hibernation or torpor covering a large range of temperatures. Here, we show that in the absence of MAP6, microtubules in cells below 20 °C rapidly depolymerize in a temperature-dependent manner whereas they are stabilized in the presence of MAP6. We further show that in cells, MAP6-F binding to and stabilization of microtubules is temperature- dependent and very dynamic, suggesting a direct effect of the temperature on the formation of microtubule/MAP6 complex. We also demonstrate using purified proteins that MAP6-F binds directly to microtubules through its Mc domain. This binding is temperature-dependent and coincides with progressive conformational changes of the Mc domain as revealed by circular dichroism. Thus, MAP6 might serve as a temperature sensor adapting its conformation according to the temperature to maintain the cellular microtubule network in organisms exposed to temperature decrease

Cap-Gly Proteins at Microtubule Plus Ends: Is EB1 Detyrosination Involved?

Localization of CAP-Gly proteins such as CLIP170 at microtubule+ends results from their dual interaction with α-tubulin and EB1 through their C-terminal amino acids −EEY. Detyrosination (cleavage of the terminal tyrosine) of α-tubulin by tubulin-carboxypeptidase abolishes CLIP170 binding. Can detyrosination affect EB1 and thus regulate the presence of CLIP170 at microtubule+ends as well? We developed specific antibodies to discriminate tyrosinated vs detyrosinated forms of EB1 and detected only tyrosinated EB1 in fibroblasts, astrocytes, and total brain tissue. Over-expressed EB1 was not detyrosinated in cells and chimeric EB1 with the eight C-terminal amino acids of α-tubulin was only barely detyrosinated. Our results indicate that detyrosination regulates CLIPs interaction with α-tubulin, but not with EB1. They highlight the specificity of carboxypeptidase toward tubulin

New insights into microtubule elongation mechanisms

Microtubules are cytoskeletal structures in the cytoplasm of eukaryotic cells, and their highly dynamic properties are essential to perform a wide variety of vital functions in cells. Microtubule growth proceeds through the endwise addition of nucleotide-bound tubulin molecules. It has largely been assumed that only tubulin dimers can incorporate into microtubules, and that the chemical state of the nucleotide is crucial for the incorporation. Recent observations reveal that both tubulin dimers and oligomers can add to microtubule ends and that the chemical state of the nucleotide is not decisive for tubulin addition. Together with structural studies of tubulin, these results show tubulin assembly polymorphism, which could play a crucial role in microtubule-dependent cellular functions

Cellular disorders induced by high magnetic fields.: High Magnetic Fields in Biology

International audiencePURPOSE: To evaluate whether static high magnetic fields (HMFs), in the range of 10-17 T, affect the cytoskeleton and cell organization in different types of mammalian cells, including fibroblasts, epithelial cells, and differentiating neurons. MATERIALS AND METHODS: Cells were exposed to HMF for 30 or 60 minutes and subsequently assessed for viability. Cytoskeleton arrays and focal adhesions were visualized using immunofluorescence microscopy. RESULTS: Cell exposure to HMF over 10 T in the case of cycling cells, and over 15 T in the case of neurons, affected cell viability, apparently because of cell detachment from culture dishes. In the remaining adherent cells, the organization of actin assemblies was perturbed, and both cell adhesion and spreading were impaired. Moreover, in the case of neurons, exposure to HMF induced growth cone retraction and delayed cell differentiation. CONCLUSION: Cell exposure to HMF (over 10T and 15 T in the case of cycling cells and neurons, respectively) affects the cell cytoskeleton, with deleterious effects on cell viability, organization, and differentiation. Further studies are needed to determine whether such perturbations, as observed here in cultured cells, have consequences in whole animals

Study of endogenous EB1 C-termini in fibroblasts and brain from wild type and TTL-deficient mouse.

<p>Western-blot analysis of the indicated control proteins (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0033490#pone-0033490-g001" target="_blank">figure 1</a>) or extracts. (A) Immunoprecipitation of endogenous EB1 from wild type (TTL^+/+) or TTL-deficient MEFs using anti-total EB1 antibody, and analysis with anti-Tyr EB1 (1∶15000), anti-detyr EB1 (1∶200), and anti-total EB1 (1∶2000). EX: crude extract; SN: supernatant after immunoprecipitation; IP: immunoprecipitated fraction. No detyrosinated EB1 could be detected in the IP fractions. Note that anti-total EB1 antibody being less sensitive than anti-Tyr EB1, EB1 failed to be detected in crude extract (upper panel). (B) Immunodepletion of tyrosinated EB1 with anti-Tyr EB1 (IP 1 to 4) in brain extracts from wild type and TTL-knockout mice, followed by immunoprecipitation of the remaining EB1 with anti-total EB1 (IP5), and analysis with anti-total EB1 (1∶2000). No remaining EB1 could be detected after tyrosinated-EB1 immunodepletion. (C) Tyrosinated and detyrosinated tubulin pools in brain extracts from wild type and TTL-deficient mice were analyzed using anti-α tubulin (1∶10,000), anti-tyrosinated tubulin (YL_1/2, 1∶20,000), and anti-detyrosinated tubulin (L₄, 1∶20,000).</p

Analysis of C-termini of recombinant EB1 forms overexpressed in wild type and TTL-deficient fibroblasts.

<p>Western-blot analysis of the indicated control proteins (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0033490#pone-0033490-g001" target="_blank">figure 1</a>) and of fractions of immunoprecipitation experiments carried out on cells transfected with cDNA encoding different EB1 forms. EX: crude extract; SN: supernatant after immunoprecipitation; IP: immunoprecipitated fraction. (A) transfection of fibroblasts (NIH3T3) with plasmids encoding tyrosinated EB1 fused with GFP at the N-terminus (GFP-EB1), followed by immunoprecipitation using anti-GFP antibody and analysis using anti-Tyr EB1 (1∶15000) and anti-deTyr EB1 (1∶200). No detyrosinated GFP-EB1 could be detected. (B) Transfection of fibroblasts with cDNA encoding GFP-EB1 ending with the C-terminus of α-tubulin GEEEGEEY (GFP-EB1-CterTub), followed by immunoprecipitation with anti-GFP antibody and analysis using anti-Tyr Tub (1∶20,000) and anti-deTyr Tub (1∶20,000). NIH3T3 were used as TTL^+/+ cells and MEFs isolated from TTL null mice were used as TTL^−/−. A very low quantity of detyrosinated protein ending with α-tubulin residues was detected (upper band in IP fractions of lower panel).</p

Analysis of developed anti-EB1 antibodies compared to the known anti-tubulin antibodies.

<p>(A) Western-blot analysis of the indicated proteins (15 ng) separated on 10% SDS-PAGE using a commercial anti-EB1 antibody (anti-total EB1, raised against amino-acids 107–268 of mouse EB1), the presently developed antibodies (anti-Tyr EB1 and anti-deTyr EB1), and tubulin antibodies. Detyrosinated EB1 was obtained from recombinant EB1 using carboxypeptidase A. Tyrosinated and detyrosinated tubulin were obtained from purified brain tubulin, using respectively TTL and carboxypeptidase A. Both anti-Tyr EB1 and anti-deTyr EB1 are highly specific. (B) Double immunostaining with anti-total EB1 antibody and anti-Tyr EB1 on fibroblasts after transfection of plasmids allowing expression of either tyrosinated or detyrosinated EB1 with EGFP at the N-terminus. The transfected cells were detected by EGFP signal. Anti-Tyr EB1 is highly specific of tyrosinated form of EB1. (C) Immunostaining of endogenous EB1 in astrocytes with anti-Tyr EB1 and anti-total EB1.</p