Articles de revues : « Tubulins »

1

Shu, H. B., et H. C. Joshi. « Gamma-tubulin can both nucleate microtubule assembly and self-assemble into novel tubular structures in mammalian cells. » Journal of Cell Biology 130, n^o 5 (1 septembre 1995) : 1137–47. http://dx.doi.org/10.1083/jcb.130.5.1137.

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alpha-, beta-, and gamma-tubulins are evolutionarily highly conserved members of the tubulin gene superfamily. While the abundant members, alpha- and beta-tubulins, constitute the building blocks of cellular microtubule polymers, gamma-tubulin is a low abundance protein which localized to the pericentriolar material and may play a role in microtubule assembly. To test whether gamma-tubulin mediates the nucleation of microtubule assembly in vivo, and co-assembles with alpha- and beta-tubulins into microtubules or self-assembles into macro-molecular structures, we experimentally elevated the expression of gamma-tubulin in the cell cytoplasm. In most cells, overexpression of gamma-tubulin causes a dramatic reorganization of the cellular microtubule network. Furthermore, we show that when overexpressed, gamma-tubulin causes ectopic nucleation of microtubules which are not associated with the centrosome. In a fraction of cells, gamma-tubulin self-assembles into novel tubular structures with a diameter of approximately 50 nm (named gamma-tubules). Furthermore, unlike microtubules, gamma-tubules are resistant to cold or drug induced depolymerization. These data provide evidence that gamma-tubulin can cause nucleation of microtubule assembly and can self-assemble into novel tubular structures.

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Burland, T. G., E. C. Paul, M. Oetliker et W. F. Dove. « A gene encoding the major beta tubulin of the mitotic spindle in Physarum polycephalum plasmodia ». Molecular and Cellular Biology 8, n^o 3 (mars 1988) : 1275–81. http://dx.doi.org/10.1128/mcb.8.3.1275-1281.1988.

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The multinucleate plasmodium of Physarum polycephalum is unusual among eucaryotic cells in that it uses tubulins only in mitotic-spindle microtubules; cytoskeletal, flagellar, and centriolar microtubules are absent in this cell type. We have identified a beta-tubulin cDNA clone, beta 105, which is shown to correspond to the transcript of the betC beta-tubulin locus and to encode beta 2 tubulin, the beta tubulin expressed specifically in the plasmodium and used exclusively in the mitotic spindle. Physarum amoebae utilize tubulins in the cytoskeleton, centrioles, and flagella, in addition to the mitotic spindle. Sequence analysis shows that beta 2 tubulin is only 83% identical to the two beta tubulins expressed in amoebae. This compares with 70 to 83% identity between Physarum beta 2 tubulin and the beta tubulins of yeasts, fungi, alga, trypanosome, fruit fly, chicken, and mouse. On the other hand, Physarum beta 2 tubulin is no more similar to, for example, Aspergillus beta tubulins than it is to those of Drosophila melanogaster or mammals. Several eucaryotes express at least one widely diverged beta tubulin as well as one or more beta tubulins that conform more closely to a consensus beta-tubulin sequence. We suggest that beta-tubulins diverge more when their expression pattern is restricted, especially when this restriction results in their use in fewer functions. This divergence among beta tubulins could have resulted through neutral drift. For example, exclusive use of Physarum beta 2 tubulin in the spindle may have allowed more amino acid substitutions than would be functionally tolerable in the beta tubulins that are utilized in multiple microtubular organelles. Alternatively, restricted use of beta tubulins may allow positive selection to operate more freely to refine beta-tubulin function.

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Burland, T. G., E. C. Paul, M. Oetliker et W. F. Dove. « A gene encoding the major beta tubulin of the mitotic spindle in Physarum polycephalum plasmodia. » Molecular and Cellular Biology 8, n^o 3 (mars 1988) : 1275–81. http://dx.doi.org/10.1128/mcb.8.3.1275.

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The multinucleate plasmodium of Physarum polycephalum is unusual among eucaryotic cells in that it uses tubulins only in mitotic-spindle microtubules; cytoskeletal, flagellar, and centriolar microtubules are absent in this cell type. We have identified a beta-tubulin cDNA clone, beta 105, which is shown to correspond to the transcript of the betC beta-tubulin locus and to encode beta 2 tubulin, the beta tubulin expressed specifically in the plasmodium and used exclusively in the mitotic spindle. Physarum amoebae utilize tubulins in the cytoskeleton, centrioles, and flagella, in addition to the mitotic spindle. Sequence analysis shows that beta 2 tubulin is only 83% identical to the two beta tubulins expressed in amoebae. This compares with 70 to 83% identity between Physarum beta 2 tubulin and the beta tubulins of yeasts, fungi, alga, trypanosome, fruit fly, chicken, and mouse. On the other hand, Physarum beta 2 tubulin is no more similar to, for example, Aspergillus beta tubulins than it is to those of Drosophila melanogaster or mammals. Several eucaryotes express at least one widely diverged beta tubulin as well as one or more beta tubulins that conform more closely to a consensus beta-tubulin sequence. We suggest that beta-tubulins diverge more when their expression pattern is restricted, especially when this restriction results in their use in fewer functions. This divergence among beta tubulins could have resulted through neutral drift. For example, exclusive use of Physarum beta 2 tubulin in the spindle may have allowed more amino acid substitutions than would be functionally tolerable in the beta tubulins that are utilized in multiple microtubular organelles. Alternatively, restricted use of beta tubulins may allow positive selection to operate more freely to refine beta-tubulin function.

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Khabudaev, Kirill V., Darya P. Petrova, Yekaterina D. Bedoshvili, Yelena V. Likhoshway et Mikhail A. Grachev. « Molecular Evolution of Tubulins in Diatoms ». International Journal of Molecular Sciences 23, n^o 2 (6 janvier 2022) : 618. http://dx.doi.org/10.3390/ijms23020618.

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Microtubules are formed by α- and β-tubulin heterodimers nucleated with γ-tubulin. Tubulins are conserved eukaryotic proteins. Previously, it was shown that microtubules are involved in diatom silica frustule morphogenesis. Diatom frustules are varied, and their morphology is species-specific. Despite the attractiveness of the problem of elucidating the molecular mechanisms of genetically programmed morphogenesis, the structure and evolution of diatom tubulins have not been studied previously. Based on available genomic and transcriptome data, we analyzed the phylogeny of the predicted amino acid sequences of diatom α-, β- and γ-tubulins and identified five groups for α-tubulins, six for β-tubulins and four for γ-tubulins. We identified characteristic amino acids of each of these groups and also analyzed possible posttranslational modification sites of diatom tubulins. According to our results, we assumed what changes occurred in the diatom tubulin structures during their evolution. We also identified which tubulin groups are inherent in large diatom taxa. The similarity between the evolution of diatom tubulins and the evolution of diatoms suggests that molecular changes in α-, β- and γ-tubulins could be one of the factors in the formation of a high morphological diversity of diatoms.

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Zhou, Yujun, Jianqiang Xu, Yuanye Zhu, Yabing Duan et Mingguo Zhou. « Mechanism of Action of the Benzimidazole Fungicide on Fusarium graminearum : Interfering with Polymerization of Monomeric Tubulin But Not Polymerized Microtubule ». Phytopathology® 106, n^o 8 (août 2016) : 807–13. http://dx.doi.org/10.1094/phyto-08-15-0186-r.

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Tubulins are the proposed target of clinically relevant anticancer drugs, anthelmintic, and fungicide. β2-tubulin of the plant pathogen Fusarium graminearum was considered as the target of benzimidazole compounds by homology modeling in our previous work. In this study, α1-, α2-, and β2-tubulin of F. graminearum were produced in Escherichia coli. Three benzimidazole compounds (carbendazim, benomyl, and thiabendazole) interacted with the recombinant β2-tubulin and reduced the maximum fluorescence intensity of 2 μM β2-tubulin 47, 50, and 25%, respectively, at saturation of compound-tubulin complexes. Furthermore, carbendazim significantly inhibited the polymerization of α1-/β2-tubulins and α2-/β2-tubulins 90.9 ± 0.4 and 93.5 ± 0.05%, respectively, in vitro. A similar result appeared with benomyl on the polymerization of α1-/β2-tubulins and α2-/β2-tubulins at 89.9 ± 0.1% and 92.6 ± 1.2% inhibition ratios, respectively. In addition, thiabendazole inhibited 81.6 ± 1% polymerization of α1-/β2-tubulins, whereas it had less effect on α2-/β2-tubulin polymerization, with 20.1 ± 1.9% inhibition ratio. However, the three compounds cannot destabilize the polymerized microtubule. To illuminate the issue, mapping the carbendazim binding sites and β/α subunit interface on β/α-tubulin complexes by homology modeling showed that the two domains were closed to each other. Understanding the nature of the interaction between benzimidazole compounds and F. graminearum tubulin is fundamental for the development of tubulin-specific anti-F. graminearum compounds.

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Rudolph, J. E., M. Kimble, H. D. Hoyle, M. A. Subler et E. C. Raff. « Three Drosophila beta-tubulin sequences : a developmentally regulated isoform (beta 3), the testis-specific isoform (beta 2), and an assembly-defective mutation of the testis-specific isoform (B2t8) reveal both an ancient divergence in metazoan isotypes and structural constraints for beta-tubulin function ». Molecular and Cellular Biology 7, n^o 6 (juin 1987) : 2231–42. http://dx.doi.org/10.1128/mcb.7.6.2231-2242.1987.

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The genomic DNA sequence and deduced amino acid sequence are presented for three Drosophila melanogaster beta-tubulins: a developmentally regulated isoform beta 3-tubulin, the wild-type testis-specific isoform beta 2-tubulin, and an ethyl methanesulfonate-induced assembly-defective mutation of the testis isoform, B2t8. The testis-specific beta 2-tubulin is highly homologous to the major vertebrate beta-tubulins, but beta 3-tubulin is considerably diverged. Comparison of the amino acid sequences of the two Drosophila isoforms to those of other beta-tubulins indicates that these two proteins are representative of an ancient sequence divergence event which at least preceded the split between lines leading to vertebrates and invertebrates. The intron/exon structures of the genes for beta 2- and beta 3-tubulin are not the same. The structure of the gene for the variant beta 3-tubulin isoform, but not that of the testis-specific beta 2-tubulin gene, is similar to that of vertebrate beta-tubulins. The mutation B2t8 in the gene for the testis-specific beta 2-tubulin defines a single amino acid residue required for normal assembly function of beta-tubulin. The sequence of the B2t8 gene is identical to that of the wild-type gene except for a single nucleotide change resulting in the substitution of lysine for glutamic acid at residue 288. This position falls at the junction between two major structural domains of the beta-tubulin molecule. Although this hinge region is relatively variable in sequence among different beta-tubulins, the residue corresponding to glu 288 of Drosophila beta 2-tubulin is highly conserved as an acidic amino acid not only in all other beta-tubulins but in alpha-tubulins as well.

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Rudolph, J. E., M. Kimble, H. D. Hoyle, M. A. Subler et E. C. Raff. « Three Drosophila beta-tubulin sequences : a developmentally regulated isoform (beta 3), the testis-specific isoform (beta 2), and an assembly-defective mutation of the testis-specific isoform (B2t8) reveal both an ancient divergence in metazoan isotypes and structural constraints for beta-tubulin function. » Molecular and Cellular Biology 7, n^o 6 (juin 1987) : 2231–42. http://dx.doi.org/10.1128/mcb.7.6.2231.

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The genomic DNA sequence and deduced amino acid sequence are presented for three Drosophila melanogaster beta-tubulins: a developmentally regulated isoform beta 3-tubulin, the wild-type testis-specific isoform beta 2-tubulin, and an ethyl methanesulfonate-induced assembly-defective mutation of the testis isoform, B2t8. The testis-specific beta 2-tubulin is highly homologous to the major vertebrate beta-tubulins, but beta 3-tubulin is considerably diverged. Comparison of the amino acid sequences of the two Drosophila isoforms to those of other beta-tubulins indicates that these two proteins are representative of an ancient sequence divergence event which at least preceded the split between lines leading to vertebrates and invertebrates. The intron/exon structures of the genes for beta 2- and beta 3-tubulin are not the same. The structure of the gene for the variant beta 3-tubulin isoform, but not that of the testis-specific beta 2-tubulin gene, is similar to that of vertebrate beta-tubulins. The mutation B2t8 in the gene for the testis-specific beta 2-tubulin defines a single amino acid residue required for normal assembly function of beta-tubulin. The sequence of the B2t8 gene is identical to that of the wild-type gene except for a single nucleotide change resulting in the substitution of lysine for glutamic acid at residue 288. This position falls at the junction between two major structural domains of the beta-tubulin molecule. Although this hinge region is relatively variable in sequence among different beta-tubulins, the residue corresponding to glu 288 of Drosophila beta 2-tubulin is highly conserved as an acidic amino acid not only in all other beta-tubulins but in alpha-tubulins as well.

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8

Xie, Yixin, et Lin Li. « Computational Study on E-Hooks of Tubulins in the Binding Process with Kinesin ». International Journal of Molecular Sciences 23, n^o 4 (12 février 2022) : 2035. http://dx.doi.org/10.3390/ijms23042035.

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Cargo transport within cells is essential to healthy cells, which requires microtubules-based motors, including kinesin. The C-terminal tails (E-hooks) of alpha and beta tubulins of microtubules have been proven to play important roles in interactions between the kinesins and tubulins. Here, we implemented multi-scale computational methods in E-hook-related analyses, including flexibility investigations of E-hooks, binding force calculations at binding interfaces between kinesin and tubulins, electrostatic potential calculations on the surface of kinesin and tubulins. Our results show that E-hooks have several functions during the binding process: E-hooks utilize their own high flexibilities to increase the chances of reaching a kinesin; E-hooks help tubulins to be more attractive to kinesin. Besides, we also observed the differences between alpha and beta tubulins: beta tubulin shows a higher flexibility than alpha tubulin; beta tubulin generates stronger attractive forces (about twice the strengths) to kinesin at different distances, no matter with E-hooks in the structure or not. Those facts may indicate that compared to alpha tubulin, beta tubulin contributes more to attracting and catching a kinesin to microtubule. Overall, this work sheds the light on microtubule studies, which will also benefit the treatments of neurodegenerative diseases, cancer treatments, and preventions in the future.

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Lajoie-Mazenc, I., C. Detraves, V. Rotaru, M. Gares, Y. Tollon, C. Jean, M. Julian, M. Wright et B. Raynaud-Messina. « A single gamma-tubulin gene and mRNA, but two gamma-tubulin polypeptides differing by their binding to the spindle pole organizing centres ». Journal of Cell Science 109, n^o 10 (1 octobre 1996) : 2483–92. http://dx.doi.org/10.1242/jcs.109.10.2483.

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Cells of eukaryotic organisms exhibit microtubules with various functions during the different developmental stages. The identification of multiple forms of alpha- and beta-tubulins had raised the question of their possible physiological roles. In the myxomycete Physarum polycephalum a complex polymorphism for alpha- and beta-tubulins has been correlated with a specific developmental expression pattern. Here, we have investigated the potential heterogeneity of gamma-tubulin in this organism. A single gene, with 3 introns and 4 exons, and a single mRNA coding for gamma-tubulin were detected. They coded for a polypeptide of 454 amino acids, with a predicted molecular mass of 50,674, which presented 64–76% identity with other gamma-tubulins. However, immunological studies identified two gamma-tubulin polypeptides, both present in the two developmental stages of the organism, uninucleate amoebae and multinucleate plasmodia. The two gamma-tubulins, called gamma s- and gamma f-tubulin for slow and fast electrophoretic mobility, exhibited apparent molecular masses of 52,000 and 50,000, respectively. They were recognized by two antibodies (R70 and JH46) raised against two distinct conserved sequences of gamma-tubulins. They were present both in the preparations of amoebal centrosomes possessing two centrioles and in the preparations of plasmodial nuclear metaphases devoid of structurally distinct polar structures. These two gamma-tubulins exhibited different sedimentation properties as shown by ultracentrifugation and sedimentation in sucrose gradients. Moreover, gamma s-tubulin was tightly bound to microtubule organizing centers (MTOCs) while gamma f-tubulin was loosely associated with these structures. This first demonstration of the presence of two gamma-tubulins with distinct properties in the same MTOC suggests a more complex physiological role than previously assumed.

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Chumová, Jana, Hana Kourová, Lucie Trögelová, Petr Halada et Pavla Binarová. « Microtubular and Nuclear Functions of γ-Tubulin : Are They LINCed ? » Cells 8, n^o 3 (19 mars 2019) : 259. http://dx.doi.org/10.3390/cells8030259.

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γ-Tubulin is a conserved member of the tubulin superfamily with a function in microtubule nucleation. Proteins of γ-tubulin complexes serve as nucleation templates as well as a majority of other proteins contributing to centrosomal and non-centrosomal nucleation, conserved across eukaryotes. There is a growing amount of evidence of γ-tubulin functions besides microtubule nucleation in transcription, DNA damage response, chromatin remodeling, and on its interactions with tumor suppressors. However, the molecular mechanisms are not well understood. Furthermore, interactions with lamin and SUN proteins of the LINC complex suggest the role of γ-tubulin in the coupling of nuclear organization with cytoskeletons. γ-Tubulin that belongs to the clade of eukaryotic tubulins shows characteristics of both prokaryotic and eukaryotic tubulins. Both human and plant γ-tubulins preserve the ability of prokaryotic tubulins to assemble filaments and higher-order fibrillar networks. γ-Tubulin filaments, with bundling and aggregating capacity, are suggested to perform complex scaffolding and sequestration functions. In this review, we discuss a plethora of γ-tubulin molecular interactions and cellular functions, as well as recent advances in understanding the molecular mechanisms behind them.

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Schneider, A., U. Plessmann et K. Weber. « Subpellicular and flagellar microtubules of Trypanosoma brucei are extensively glutamylated ». Journal of Cell Science 110, n^o 4 (15 février 1997) : 431–37. http://dx.doi.org/10.1242/jcs.110.4.431.

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To determine the spectrum of tubulin variants in cytoskeletons of Trypanosoma brucei carboxy-terminal fragments of alpha- and beta-tubulin were isolated and characterized by sequencing and mass spectrometry. All variants arise by posttranslational modifications. We confirm the presence of tyrosinated and detyrosinated alpha-tubulin. Unexpectedly, but in line with its sequence, beta-tubulin also occurs with and without its carboxy-terminal tyrosine. Both tyrosinated and detyrosinated alpha- and beta-tubulins are extensively glutamylated. Unglutamylated tubulins are only trace components of the cytoskeletal microtubules. The maximal numbers of glutamyl residues in the lateral chain are 15 and 6 for alpha- and beta-tubulin, respectively. The oligoglutamyl side chain is linked via an isopeptide bond to glutamic acid residues 445 of alpha- and 435 of beta-tubulin. The same sites are used in glutamylated tubulins of mammalian brain. No tubulin variants based on polyglycylation are detected in cytoskeletal preparations or in isolated flagella. Tubulin specific incorporation of radioactive glutamate but not of glycine is observed when protein biosynthesis is completely inhibited in Trypanosoma cells. Possible reasons for the absence of polyglycylated tubulins from the trypanosomal axoneme are discussed. Finally we show that lysine 40 of the flagellar alpha-tubulin is completely acetylated.

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Trivinos-Lagos, L., T. Ohmachi, C. Albrightson, R. G. Burns, H. L. Ennis et R. L. Chisholm. « The highly divergent alpha- and beta-tubulins from Dictyostelium discoideum are encoded by single genes ». Journal of Cell Science 105, n^o 4 (1 août 1993) : 903–11. http://dx.doi.org/10.1242/jcs.105.4.903.

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As a step in the characterization of the microtubule system of Dictyostelium discoideum, we have isolated and sequenced full-length cDNA clones that encode the Dictyostelium alpha- and beta-tubulins, as well as the Dictyostelium alpha-tubulin gene. Southern blot analysis suggests that Dictyostelium is unusual in that its genome contains single alpha- and beta-tubulin genes, rather than the multi-gene family common in most eukaryotic organisms. The complete alpha-tubulin cDNA contains 1558 nucleotides, with an open reading frame, that encode a protein of 457 amino acids. The complete beta-tubulin cDNA contains 1572 nucleotides and encodes a protein of 456 amino acids. Analysis of the deduced protein sequences indicates that while there is a significant degree of sequence similarity between the Dictyostelium tubulins and other known tubulins, the Dictyostelium alpha-tubulin displays the greatest sequence divergence yet described. Single alpha- and beta-tubulin transcripts are detected by northern blot analysis during all stages of Dictyostelium development. The highest levels of message accumulate late in germinating spores and vegetative amoebae. Despite changes in alpha- and beta-tubulin mRNA levels, protein levels remain constant throughout development. We have expressed the carboxy-terminal two-thirds of the alpha- and beta-tubulins as trpE fusions in Escherichia coli and used this protein to produce polyclonal antisera specific for the Dictyostelium alpha- and beta-tubulins. These antisera recognize one alpha- and two beta-tubulin spots on western blots of 2-D gels and, by indirect immunofluorescence, both recognize the interphase and mitotic microtubule arrays in vegetative amoebae.

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Makarova, Liubov, et Alena Korshunova. « Abstract P-36 : Structural Analysis of Conformational Changes of Bacterial and Eukaryotic Tubulins ». International Journal of Biomedicine 11, Suppl_1 (1 juin 2021) : S27—S28. http://dx.doi.org/10.21103/ijbm.11.suppl_1.p36.

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Background: Eukaryotic α- and β-tubulin proteins stand out among tubulin-like proteins by their ability to form hollow dynamically unstable microtubules (MT) with 13 protofilaments. Microtubules are part of the cell cytoskeleton and play a key role in chromosome division in mitosis. A considerable amount of anticancer drugs works on microtubules level breaking its dynamic. But the mechanism of dynamic instability and works of these drugs remains unknown. Bacteria of the genus Prostecobacter have unique bacterial tubulins (BtubA/B) capable to form hollow dynamically unstable 5 protofilament MTs (miniMT). Instead of great differences, both tubulins have many common features. Eukaryotic tubulin was known to have structural changes through GTP hydrolysis (compactization for approximately 2 Å and a twist for 0,1˚). «Anchor point» structure in alpha-tubulin was noticed to be a fixed point in this movement. Methods: We performed comparative structural analysis of BtubA/B and α- and β-tubulin proteins using USCF Chimera10 and MEGA X software. This data was obtained due to a comparison of 3 structures of microtubules with different nucleotides [pdb6DPU, 6DPV, 6DPW] and two structures for bacterial tubulins (miniMT [pdb5o09] and BtubA/B-dimer [pdb2BTQ]). Results: We noticed that bacterial tubulins form shorter protofilaments in miniMT than eukaryotic ones. It can be explained as compaction in two sites instead of one site in eukaryotic MT. Also, the most motionless point of min MT turned out the same "anchor point." Phylogenetic analysis showed that this structure is very conservative in these orthologs. Moreover, the final state of both tubulins (GDP) repeats each other. Conclusion: Our results suggest that bacterial tubulin can have movements through GTP hydrolysis similar to eukaryotic one. And it means that despite different amino acid sequences, bacterial and eukaryotic tubulins have similar keys structures for dynamic instability.

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Liu, Congshan, Jiaqing Yao, Jianhai Yin, Jian Xue et Haobing Zhang. « Recombinant α- and β-tubulin from Echinococcus granulosus : expression, purification and polymerization ». Parasite 25 (2018) : 62. http://dx.doi.org/10.1051/parasite/2018063.

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Echinococcosis, which causes a high disease burden and is of great public health significance, is caused by the larval stage of Echinococcus species. It has been suggested that tubulin is the target of benzimidazoles, the only drugs for the treatment of echinococcosis. This study evaluated the characteristics of tubulins from Echinococcus granulosus. The full-length cDNAs of E. granulosus α- and β-tubulin isoforms were cloned by reverse transcription PCR from protoscolex RNA. Then, these two tubulin isoforms (α9 and β4) were recombinantly expressed as insoluble inclusion bodies in Escherichia coli. Nickel affinity chromatography was used to purify and refold the contents of these inclusion bodies as active proteins. The polymerization of tubulins was monitored by UV spectrophotometry (A350) and confirmed by confocal microscopy and transmission electron microscopy (TEM). Nucleotide sequence analysis revealed that E. granulosus 1356 bp α9-tubulin and 1332 bp β4-tubulin encode corresponding proteins of 451 and 443 amino acids. The average yields of α9- and β4-tubulin were 2.0–3.0 mg/L and 3.5–5.0 mg/L of culture, respectively. Moreover, recombinant α9- and β4-tubulin were capable of polymerizing into microtubule-like structures under appropriate conditions in vitro. These recombinant tubulins could be helpful for screening anti-Echinococcus compounds targeting the tubulins of E. granulosus.

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Chu, Chih-Wen, Fajian Hou, Junmei Zhang, Lilian Phu, Alex V. Loktev, Donald S. Kirkpatrick, Peter K. Jackson, Yingming Zhao et Hui Zou. « A novel acetylation of β-tubulin by San modulates microtubule polymerization via down-regulating tubulin incorporation ». Molecular Biology of the Cell 22, n^o 4 (15 février 2011) : 448–56. http://dx.doi.org/10.1091/mbc.e10-03-0203.

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Dynamic instability is a critical property of microtubules (MTs). By regulating the rate of tubulin polymerization and depolymerization, cells organize the MT cytoskeleton to accommodate their specific functions. Among many processes, posttranslational modifications of tubulin are implicated in regulating MT functions. Here we report a novel tubulin acetylation catalyzed by acetyltransferase San at lysine 252 (K252) of β-tubulin. This acetylation, which is also detected in vivo, is added to soluble tubulin heterodimers but not tubulins in MTs. The acetylation-mimicking K252A/Q mutants were incorporated into the MT cytoskeleton in HeLa cells without causing any obvious MT defect. However, after cold-induced catastrophe, MT regrowth is accelerated in San-siRNA cells while the incorporation of acetylation-mimicking mutant tubulins is severely impeded. K252 of β-tubulin localizes at the interface of α-/β-tubulins and interacts with the phosphate group of the α-tubulin-bound GTP. We propose that the acetylation slows down tubulin incorporation into MTs by neutralizing the positive charge on K252 and allowing tubulin heterodimers to adopt a conformation that disfavors tubulin incorporation.

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Westermann, S., A. Schneider, E. K. Horn et K. Weber. « Isolation of tubulin polyglutamylase from Crithidia ; binding to microtubules and tubulin, and glutamylation of mammalian brain alpha- and beta-tubulins ». Journal of Cell Science 112, n^o 13 (1 juillet 1999) : 2185–93. http://dx.doi.org/10.1242/jcs.112.13.2185.

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Trypanosomatids have a striking cage-like arrangement of submembraneous microtubules. We previously showed that alpha- and beta- tubulins of these stable microtubules are extensively modified by polyglutamylation. Cytoskeletal microtubular preparations obtained by Triton extraction of Leishmania tarentolae and Crithidia fasciculata retain an enzymatic activity that incorporates radioactive glutamic acid in a Mg2+-ATP-dependent manner into alpha- and beta-tubulins. The tubulin polyglutamylase is extracted by 0.25 M salt. The Crithidia enzyme can be purified by ATP-affinity chromatography, glycerol-gradient centrifugation and ion-exchange chromatography. After extraction from the microtubular cytoskeleton the glutamylase forms a complex with alphabeta tubulin, but behaves after removal of tubulin as a globular protein with a molecular mass of 38x10(3). In highly enriched fractions a corresponding band is the major polypeptide visible in SDS-PAGE. The enzyme from Crithidia recognises mammalian brain tubulin, where it incorporates glutamic acid preferentially into the more acidic variants of both alpha- and beta-tubulins. Synthetic peptides with an oligoglutamyl side chain, corresponding to the carboxy-terminal end of brain alpha- and beta-tubulins, are accepted by the enzyme, albeit at low efficiency. The polyglutamylase elongates the side chain by up to 3 and 5 residues, respectively. Other properties of the tubulin polyglutamylase are also discussed.

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Burke, D., P. Gasdaska et L. Hartwell. « Dominant effects of tubulin overexpression in Saccharomyces cerevisiae ». Molecular and Cellular Biology 9, n^o 3 (mars 1989) : 1049–59. http://dx.doi.org/10.1128/mcb.9.3.1049-1059.1989.

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The consequences of altering the levels of alpha- and beta-tubulin in Saccharomyces cerevisiae were examined by constructing fusions of the structural genes encoding the tubulins to strong galactose-inducible promoters. Overexpression of beta-tubulin (TUB2) was lethal: cells arrested in the G2 stage of the cell cycle exhibited an increased frequency of chromosome loss, were devoid of microtubules, and accumulated beta-tubulin in a novel structure. Overexpression of the major alpha-tubulin gene (TUB1) was not lethal and did not affect chromosome segregation. The rate of alpha-tubulin mRNA and protein synthesis was increased, but the protein did not accumulate. Overexpression of both alpha- and beta-tubulin together resulted in arrested cell division, and cells accumulated excess tubules that contained both alpha- and beta-tubulin. Transient overexpression of both tubulins resulted in a high frequency of chromosome loss. These data suggest that strong selective pressure exists to prevent excess accumulation of microtubules or beta-tubulin and suggest a model by which this goal may be achieved by selective degradation of unassembled alpha-tubulin. Furthermore, the phenotype of beta-tubulin overexpression is similar to the phenotype of a beta-tubulin deficiency. These results add to a number of recent studies demonstrating that mutant phenotypes generated by overexpression can be informative about the function of the gene product.

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Burke, D., P. Gasdaska et L. Hartwell. « Dominant effects of tubulin overexpression in Saccharomyces cerevisiae. » Molecular and Cellular Biology 9, n^o 3 (mars 1989) : 1049–59. http://dx.doi.org/10.1128/mcb.9.3.1049.

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The consequences of altering the levels of alpha- and beta-tubulin in Saccharomyces cerevisiae were examined by constructing fusions of the structural genes encoding the tubulins to strong galactose-inducible promoters. Overexpression of beta-tubulin (TUB2) was lethal: cells arrested in the G2 stage of the cell cycle exhibited an increased frequency of chromosome loss, were devoid of microtubules, and accumulated beta-tubulin in a novel structure. Overexpression of the major alpha-tubulin gene (TUB1) was not lethal and did not affect chromosome segregation. The rate of alpha-tubulin mRNA and protein synthesis was increased, but the protein did not accumulate. Overexpression of both alpha- and beta-tubulin together resulted in arrested cell division, and cells accumulated excess tubules that contained both alpha- and beta-tubulin. Transient overexpression of both tubulins resulted in a high frequency of chromosome loss. These data suggest that strong selective pressure exists to prevent excess accumulation of microtubules or beta-tubulin and suggest a model by which this goal may be achieved by selective degradation of unassembled alpha-tubulin. Furthermore, the phenotype of beta-tubulin overexpression is similar to the phenotype of a beta-tubulin deficiency. These results add to a number of recent studies demonstrating that mutant phenotypes generated by overexpression can be informative about the function of the gene product.

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19

Inclan, Y. F., et E. Nogales. « Structural models for the self-assembly and microtubule interactions of gamma-, delta- and epsilon-tubulin ». Journal of Cell Science 114, n^o 2 (15 janvier 2001) : 413–22. http://dx.doi.org/10.1242/jcs.114.2.413.

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alphabeta-tubulin heterodimers self-assemble to form microtubules nucleated by gamma-tubulin in the cell. Gamma-tubulin is believed to recruit the alphabeta-tubulin dimers that form the minus ends of microtubules, but the molecular mechanism of this action remains a matter of heated controversy. Still less is known about the function and molecular interactions of delta-tubulin and epsilon-tubulin. delta-tubulin may seed the formation of the C triplet tubules in the basal bodies of Chlamydomonas and epsilon-tubulin is known to localize to the centrosome in a cell cycle-dependent manner. Using the structure of alphabeta tubulin as a model, we have analyzed the sequences of gamma-, delta- and epsilon-tubulin in regions corresponding to different polymerization interfaces in the tubulin alphabeta dimer. The sequence comparisons sometimes show clear conservation, pointing to similar types of contacts being functionally important for the new tubulin considered. Conversely, certain surfaces show marked differences that rule out equivalent interactions for non-microtubular tubulins. This sequence/structure analysis has led us to structural models of how these special tubulins may be involved in protein-protein contacts that affect microtubule self-assembly. delta-tubulin most likely interacts longitudinally with alpha-tubulin at the minus ends of microtubules, while epsilon-tubulin most likely binds to the plus end of beta-tubulin. Conservation of key residues in gamma-tubulin suggests that it is capable of longitudinal self-assembly. The implications for the protofilament and template models of nucleation are considered.

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20

Yu, Nuo, et Niels Galjart. « TAPping into the treasures of tubulin using novel protein production methods ». Essays in Biochemistry 62, n^o 6 (14 novembre 2018) : 781–92. http://dx.doi.org/10.1042/ebc20180033.

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Microtubules are cytoskeletal elements with important cellular functions, whose dynamic behaviour and properties are in part regulated by microtubule-associated proteins (MAPs). The building block of microtubules is tubulin, a heterodimer of α- and β-tubulin subunits. Longitudinal interactions between tubulin dimers facilitate a head-to-tail arrangement of dimers into protofilaments, while lateral interactions allow the formation of a hollow microtubule tube that mostly contains 13 protofilaments. Highly homologous α- and β-tubulin isotypes exist, which are encoded by multi-gene families. In vitro studies on microtubules and MAPs have largely relied on brain-derived tubulin preparations. However, these consist of an unknown mix of tubulin isotypes with undefined post-translational modifications. This has blocked studies on the functions of tubulin isotypes and the effects of tubulin mutations found in human neurological disorders. Fortunately, various methodologies to produce recombinant mammalian tubulins have become available in the last years, allowing researchers to overcome this barrier. In addition, affinity-based purification of tagged tubulins and identification of tubulin-associated proteins (TAPs) by mass spectrometry has revealed the ‘tubulome’ of mammalian cells. Future experiments with recombinant tubulins should allow a detailed description of how tubulin isotype influences basic microtubule behaviour, and how MAPs and TAPs impinge on tubulin isotypes and microtubule-based processes in different cell types.

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21

Kristensson, Maria Alvarado. « The Game of Tubulins ». Cells 10, n^o 4 (28 mars 2021) : 745. http://dx.doi.org/10.3390/cells10040745.

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Members of the tubulin superfamily are GTPases; the activities of GTPases are necessary for life. The members of the tubulin superfamily are the constituents of the microtubules and the γ-tubulin meshwork. Mutations in members of the tubulin superfamily are involved in developmental brain disorders, and tubulin activities are the target for various chemotherapies. The intricate functions (game) of tubulins depend on the activities of the GTP-binding domain of α-, β-, and γ-tubulin. This review compares the GTP-binding domains of γ-tubulin, α-tubulin, and β-tubulin and, based on their similarities, recapitulates the known functions and the impact of the γ-tubulin GTP-binding domain in the regulation of the γ-tubulin meshwork and cellular homeostasis.

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22

Al-Bassam, Jawdat. « Revisiting the tubulin cofactors and Arl2 in the regulation of soluble αβ-tubulin pools and their effect on microtubule dynamics ». Molecular Biology of the Cell 28, n^o 3 (février 2017) : 359–63. http://dx.doi.org/10.1091/mbc.e15-10-0694.

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Soluble αβ-tubulin heterodimers are maintained at high concentration inside eukaryotic cells, forming pools that fundamentally drive microtubule dynamics. Five conserved tubulin cofactors and ADP ribosylation factor–like 2 regulate the biogenesis and degradation of αβ-tubulins to maintain concentrated soluble pools. Here I describe a revised model for the function of three tubulin cofactors and Arl2 as a multisubunit GTP-hydrolyzing catalytic chaperone that cycles to promote αβ-tubulin biogenesis and degradation. This model helps explain old and new data indicating these activities enhance microtubule dynamics in vivo via repair or removal of αβ-tubulins from the soluble pools

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Hecht, N. B., R. J. Distel, P. C. Yelick, S. M. Tanhauser, C. E. Driscoll, E. Goldberg et K. S. Tung. « Localization of a highly divergent mammalian testicular alpha tubulin that is not detectable in brain ». Molecular and Cellular Biology 8, n^o 2 (février 1988) : 996–1000. http://dx.doi.org/10.1128/mcb.8.2.996-1000.1988.

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Sequence analysis of a mouse testicular alpha-tubulin partial cDNA, pRD alpha TT1, reveals an isotype that differs from both the somatic and the predominant testicular alpha tubulins at approximately 30% of the 212 amino acid residues determined. Although this mouse testicular cDNA retains the highly conserved sequence, Glu-Gly-Glu-Glu, found in the carboxyl termini of many alpha tubulins, the protein extends substantially beyond this sequence and does not terminate with a C-terminal tyrosine. Using rabbit antiserum prepared to a novel synthetic peptide predicted from this mouse testis alpha-tubulin cDNA, we have have detected by immunoblot and indirect immunofluorescence an antigenic epitope present in testicular alpha tubulin that is not detectable in brain alpha tubulins. We find that the antiserum specifically binds to the manchettes and meiotic spindles of the mouse testis but not with neural fibers or tubulin extracts of the adult mouse brain. These results demonstrate that at least one of the multiple alpha-tubulin isotypes of the mammalian testis is expressed and used in male germ cells but not in the brain.

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Hecht, N. B., R. J. Distel, P. C. Yelick, S. M. Tanhauser, C. E. Driscoll, E. Goldberg et K. S. Tung. « Localization of a highly divergent mammalian testicular alpha tubulin that is not detectable in brain. » Molecular and Cellular Biology 8, n^o 2 (février 1988) : 996–1000. http://dx.doi.org/10.1128/mcb.8.2.996.

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Sequence analysis of a mouse testicular alpha-tubulin partial cDNA, pRD alpha TT1, reveals an isotype that differs from both the somatic and the predominant testicular alpha tubulins at approximately 30% of the 212 amino acid residues determined. Although this mouse testicular cDNA retains the highly conserved sequence, Glu-Gly-Glu-Glu, found in the carboxyl termini of many alpha tubulins, the protein extends substantially beyond this sequence and does not terminate with a C-terminal tyrosine. Using rabbit antiserum prepared to a novel synthetic peptide predicted from this mouse testis alpha-tubulin cDNA, we have have detected by immunoblot and indirect immunofluorescence an antigenic epitope present in testicular alpha tubulin that is not detectable in brain alpha tubulins. We find that the antiserum specifically binds to the manchettes and meiotic spindles of the mouse testis but not with neural fibers or tubulin extracts of the adult mouse brain. These results demonstrate that at least one of the multiple alpha-tubulin isotypes of the mammalian testis is expressed and used in male germ cells but not in the brain.

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Lin, Zhewang, Ivana Gasic, Viswanathan Chandrasekaran, Niklas Peters, Sichen Shao, Timothy J. Mitchison et Ramanujan S. Hegde. « TTC5 mediates autoregulation of tubulin via mRNA degradation ». Science 367, n^o 6473 (14 novembre 2019) : 100–104. http://dx.doi.org/10.1126/science.aaz4352.

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Tubulins play crucial roles in cell division, intracellular traffic, and cell shape. Tubulin concentration is autoregulated by feedback control of messenger RNA (mRNA) degradation via an unknown mechanism. We identified tetratricopeptide protein 5 (TTC5) as a tubulin-specific ribosome-associating factor that triggers cotranslational degradation of tubulin mRNAs in response to excess soluble tubulin. Structural analysis revealed that TTC5 binds near the ribosome exit tunnel and engages the amino terminus of nascent tubulins. TTC5 mutants incapable of ribosome or nascent tubulin interaction abolished tubulin autoregulation and showed chromosome segregation defects during mitosis. Our findings show how a subset of mRNAs can be targeted for coordinated degradation by a specificity factor that recognizes the nascent polypeptides they encode.

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26

Saoudi, Y., I. Paintrand, L. Multigner et D. Job. « Stabilization and bundling of subtilisin-treated microtubules induced by microtubule associated proteins ». Journal of Cell Science 108, n^o 1 (1 janvier 1995) : 357–67. http://dx.doi.org/10.1242/jcs.108.1.357.

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The acidic carboxy-terminal regions of alpha- and beta-tubulin subunits are currently thought to be centrally involved in microtubule stability and in microtubule association with a variety of proteins (MAPs) such as MAP2 and tau proteins. Here, pure tubulin microtubules were exposed to subtilisin to produce polymers composed of cleaved tubulin subunits lacking carboxy termini. Polymer exposure to subtilisin was achieved in buffer conditions compatible with further tests of microtubule stability. Microtubules composed of normal alpha-tubulin and cleaved beta-tubulin were indistinguishable from control microtubules with regard to resistance to dilution-induced disassembly, to cold temperature-induced disassembly and to Ca(2+)-induced disassembly. Microtubules composed of cleaved alpha- and beta-tubulins showed normal sensitivity to dilution-induced disassembly and to low temperature-induced disassembly, but marked resistance to Ca(2+)-induced disassembly. Polymers composed of normal alpha-tubulin and cleaved beta-tubulin or of cleaved alpha- and beta-tubulins were stabilized in the presence of added MAP2, myelin basic protein and histone H1. Cleavage of tubulin carboxy termini greatly potentiated microtubule stabilization by tau proteins. We show that this potentiation of polymer stabilization can be ascribed to tau-induced microtubule bundling. In our working conditions, such bundling upon association with tau proteins occurred only in the case of microtubules composed of cleaved alpha- and beta-tubulins and triggered apparent microtubule cross-stabilization among the bundled polymers. These results, as well as immunofluorescence analysis, which directly showed interactions between subtilisin-treated microtubules and MAPs, suggest that the carboxy termini of alpha- and beta-tubulins are not primarily involved in the binding of MAPs onto microtubules. However, interactions between tubulin carboxy termini and MAPs remain possible and might be involved in the regulation of MAP-induced microtubule bundling.

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Ragusa, Maria Antonietta, Aldo Nicosia, Salvatore Costa, Caterina Casano et Fabrizio Gianguzza. « A Survey on Tubulin and Arginine Methyltransferase Families Sheds Light on P. lividus Embryo as Model System for Antiproliferative Drug Development ». International Journal of Molecular Sciences 20, n^o 9 (30 avril 2019) : 2136. http://dx.doi.org/10.3390/ijms20092136.

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Tubulins and microtubules (MTs) represent targets for taxane-based chemotherapy. To date, several lines of evidence suggest that effectiveness of compounds binding tubulin often relies on different post-translational modifications on tubulins. Among them, methylation was recently associated to drug resistance mechanisms impairing taxanes binding. The sea urchin is recognized as a research model in several fields including fertilization, embryo development and toxicology. To date, some α- and β-tubulin genes have been identified in P. lividus, while no data are available in echinoderms for arginine methyl transferases (PRMT). To evaluate the exploiting of the sea urchin embryo in the field of antiproliferative drug development, we carried out a survey of the expressed α- and β-tubulin gene sets, together with a comprehensive analysis of the PRMT gene family and of the methylable arginine residues in P. lividus tubulins. Because of their specificities, the sea urchin embryo may represent an interesting tool for dissecting mechanisms of tubulin targeting drug action. Therefore, results herein reported provide evidences supporting the P. lividus embryo as animal system for testing antiproliferative drugs.

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Morrissette, Naomi, Izra Abbaali, Chandra Ramakrishnan et Adrian B. Hehl. « The Tubulin Superfamily in Apicomplexan Parasites ». Microorganisms 11, n^o 3 (9 mars 2023) : 706. http://dx.doi.org/10.3390/microorganisms11030706.

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Microtubules and specialized microtubule-containing structures are assembled from tubulins, an ancient superfamily of essential eukaryotic proteins. Here, we use bioinformatic approaches to analyze features of tubulins in organisms from the phylum Apicomplexa. Apicomplexans are protozoan parasites that cause a variety of human and animal infectious diseases. Individual species harbor one to four genes each for α- and β-tubulin isotypes. These may specify highly similar proteins, suggesting functional redundancy, or exhibit key differences, consistent with specialized roles. Some, but not all apicomplexans harbor genes for δ- and ε-tubulins, which are found in organisms that construct appendage-containing basal bodies. Critical roles for apicomplexan δ- and ε-tubulin are likely to be limited to microgametes, consistent with a restricted requirement for flagella in a single developmental stage. Sequence divergence or the loss of δ- and ε-tubulin genes in other apicomplexans appears to be associated with diminished requirements for centrioles, basal bodies, and axonemes. Finally, because spindle microtubules and flagellar structures have been proposed as targets for anti-parasitic therapies and transmission-blocking strategies, we discuss these ideas in the context of tubulin-based structures and tubulin superfamily properties.

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Wick, S. « Maize beta tubulin genes and beta tubulins ». Cell Biology International 27, n^o 3 (2003) : 301. http://dx.doi.org/10.1016/s1065-6995(02)00332-3.

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Kubo, Tomohiro, et Toshiyuki Oda. « Electrostatic interaction between polyglutamylated tubulin and the nexin–dynein regulatory complex regulates flagellar motility ». Molecular Biology of the Cell 28, n^o 17 (15 août 2017) : 2260–66. http://dx.doi.org/10.1091/mbc.e17-05-0285.

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Tubulins undergo various posttranslational modifications. Among them, polyglutamylation is involved in the motility of eukaryotic flagella and the stability of the axonemal microtubules. However, it remains unclear where polyglutamylated tubulin localizes precisely within the axoneme and how tubulin polyglutamylation affects flagellar motility. In this study, we identified the three-dimensional localization of the polyglutamylated tubulin in Chlamydomonas flagella using antibody labeling and cryo–electron tomography. Polyglutamylated tubulins specifically located in close proximity to a microtubule-cross-bridging structure called the nexin–dynein regulatory complex (N-DRC). Because N-DRC is positively charged, we hypothesized that there is an electrostatic interaction between the polyglutamylated tubulin and the N-DRC, and therefore we mutated the amino acid sequences of DRC4 to modify the charge of the N-DRC. We found that both augmentation and reduction of the positive charge on DRC4 resulted in reduced flagellar motility. Moreover, reduced motility in a mutant with a structurally defective N-DRC was partially restored by increasing the positive charge on DRC4. These results clearly indicate that beating motion of flagella is maintained by the electrostatic cross-bridge formed between the negatively charged polyglutamylated tubulins and the positively charged N-DRC.

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Guo, Wenhan, Tolulope Ayodeji Ale, Shengjie Sun, Jason E. Sanchez et Lin Li. « A Comprehensive Study on the Electrostatic Properties of Tubulin-Tubulin Complexes in Microtubules ». Cells 12, n^o 2 (5 janvier 2023) : 238. http://dx.doi.org/10.3390/cells12020238.

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Microtubules are key players in several stages of the cell cycle and are also involved in the transportation of cellular organelles. Microtubules are polymerized by α/β tubulin dimers with a highly dynamic feature, especially at the plus ends of the microtubules. Therefore, understanding the interactions among tubulins is crucial for characterizing microtubule dynamics. Studying microtubule dynamics can help researchers make advances in the treatment of neurodegenerative diseases and cancer. In this study, we utilize a series of computational approaches to study the electrostatic interactions at the binding interfaces of tubulin monomers. Our study revealed that among all the four types of tubulin-tubulin binding modes, the electrostatic attractive interactions in the α/β tubulin binding are the strongest while the interactions of α/α tubulin binding in the longitudinal direction are the weakest. Our calculations explained that due to the electrostatic interactions, the tubulins always preferred to form α/β tubulin dimers. The interactions between two protofilaments are the weakest. Thus, the protofilaments are easily separated from each other. Furthermore, the important residues involved in the salt bridges at the binding interfaces of the tubulins are identified, which illustrates the details of the interactions in the microtubule. This study elucidates some mechanistic details of microtubule dynamics and also identifies important residues at the binding interfaces as potential drug targets for the inhibition of cancer cells.

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Linhartová, I., P. Dráber, E. Dráberová et V. Viklický. « Immunological discrimination of β-tubulin isoforms in developing mouse brain. Post-translational modification of non-class-III β-tubulins ». Biochemical Journal 288, n^o 3 (15 décembre 1992) : 919–24. http://dx.doi.org/10.1042/bj2880919.

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Individual beta-tubulin isoforms in developing mouse brain were characterized using immunoblotting, after preceding high-resolution isoelectric focusing, with monoclonal antibodies against different structural regions of beta-tubulin. Some of the antibodies reacted with a limited number of tubulin isoforms in all stages of brain development and in HeLa cells. The epitope for the TU-14 antibody was located in the isotype-defining domain and was present on the beta-tubulin isotypes of classes I, II and IV, but absent on the neuron-specific class-III isotype. The data suggest that non-class-III beta-tubulins in mouse brain are substrates for developmentally regulated post-translational modifications and that beta-tubulins of non-neuronal cells are also post-translationally modified.

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Weatherbee, J. A., G. S. May, J. Gambino et N. R. Morris. « Involvement of a particular species of beta-tubulin (beta 3) in conidial development in Aspergillus nidulans. » Journal of Cell Biology 101, n^o 3 (1 septembre 1985) : 706–11. http://dx.doi.org/10.1083/jcb.101.3.706.

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Strains of Aspergillus containing the benA22 mutation are resistant to benomyl for vegetative growth but do not produce conidia. To test whether conidiation involved an additional benomyl-sensitive tubulin (i.e., was mediated by a tubulin other than the tubulins coded for by the benA locus), a collection of mutants was produced that formed conidia in the presence of benomyl, i.e., were conidiation-resistant (CR-) mutants. We analyzed the tubulins of these CR- mutants using two-dimensional gel electrophoresis and found that the mutants lacked one species of beta-tubulin (designated beta 3). We have examined two of these mutants in detail. In crosses with strains containing wild-type tubulins, we found that the absence of the beta 3-tubulin co-segregated perfectly with the CR- phenotype. In diploids containing both the benA22 and CR- mutations, we found that the CR- phenotype was recessive and that beta 3-tubulin was present on two-dimensional gels of tubulins prepared from these diploids. In another set of crosses, these two CR- strains and seven others were first made auxotrophic for uridine and then crossed against strains that had homologously integrated a plasmid containing an incomplete internal fragment of the beta 3-tubulin gene and the pyr4 gene of Neurospora crassa (which confers uridine prototrophy on transformants). If the CR- phenotype were produced by a mutation in a gene distinct from the structural gene for beta 3-tubulin (designated the tubC gene), then crossing over should have produced some CR+ segregants among the uridine auxotrophic progeny of the second cross. All of the uridine auxotrophs from this type of cross, however, showed the CR- phenotype, suggesting that the mutation in these strains is at or closely linked to the tubC locus. The most obvious explanation of these results is that beta 3-tubulin is ordinarily used during conidiation and the presence of this species of beta-tubulin renders conidiation sensitive to benomyl. In the CR- mutants, beta 3-tubulin is absent, and in the presence of the benA22 mutation the benomyl-resistant beta 1-and/or beta 2-tubulin substitutes for beta 3 to make conidiation benomyl resistant. We discuss these results and give two models to explain the interactions between these beta-tubulin species.

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SULIMENKO, Vadym, Tetyana SULIMENKO, Slobodan POZNANOVIC, Volodymyr NECHIPORUK-ZLOY, Konrad J. BÖHM, Libor MACUREK, Eberhard UNGER et Pavel DRÁBER. « Association of brain γ-tubulins with αβ-tubulin dimers ». Biochemical Journal 365, n^o 3 (1 août 2002) : 889–95. http://dx.doi.org/10.1042/bj20020175.

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γ-Tubulin is necessary for nucleation and polar orientation of microtubules in vivo. The molecular mechanism of microtubule nucleation by γ-tubulin and the regulation of this process are not fully understood. Here we show that there are two γ-tubulin forms in the brain that are present in complexes of various sizes. Large complexes tend to dissociate in the presence of a high salt concentration. Both γ-tubulins co-polymerized with tubulin dimers, and multiple γ-tubulin bands were identified in microtubule protein preparations under conditions of non-denaturing electrophoresis. Immunoprecipitation experiments with monoclonal antibodies against γ-tubulin and α-tubulin revealed interactions of both γ-tubulin forms with tubulin dimers, irrespective of the size of complexes. We suggest that, besides small and large γ-tubulin complexes, other molecular γ-tubulin form(s) exist in brain extracts. Two-dimensional electrophoresis revealed multiple charge variants of γ-tubulin in both brain extracts and microtubule protein preparations. Post-translational modification(s) of γ-tubulins might therefore have an important role in the regulation of microtubule nucleation in neuronal cells.

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Vaughan, Susan, Terri Attwood, Miguel Navarro, Valerie Scott, Paul McKean, Andrea Baines et Keith Gull. « Tubulins in Parasite Protozoa : Epsilon and Zeta Tubulin ». Biochemical Society Transactions 28, n^o 5 (1 octobre 2000) : A218. http://dx.doi.org/10.1042/bst028a218a.

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Chin, Hang Gyeong, Pierre-Olivier Esteve, Cristian Ruse, Jiyoung Lee, Scott E. Schaus, Sriharsa Pradhan et Ulla Hansen. « The microtubule-associated histone methyltransferase SET8, facilitated by transcription factor LSF, methylates α-tubulin ». Journal of Biological Chemistry 295, n^o 14 (28 février 2020) : 4748–59. http://dx.doi.org/10.1074/jbc.ra119.010951.

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Microtubules are cytoskeletal structures critical for mitosis, cell motility, and protein and organelle transport and are a validated target for anticancer drugs. However, how tubulins are regulated and recruited to support these distinct cellular processes is incompletely understood. Posttranslational modifications of tubulins are proposed to regulate microtubule function and dynamics. Although many of these modifications have been investigated, only one prior study reports tubulin methylation and an enzyme responsible for this methylation. Here we used in vitro radiolabeling, MS, and immunoblotting approaches to monitor protein methylation and immunoprecipitation, immunofluorescence, and pulldown approaches to measure protein–protein interactions. We demonstrate that N-lysine methyltransferase 5A (KMT5A or SET8/PR-Set7), which methylates lysine 20 in histone H4, bound α-tubulin and methylated it at a specific lysine residue, Lys311. Furthermore, late SV40 factor (LSF)/CP2, a known transcription factor, bound both α-tubulin and SET8 and enhanced SET8-mediated α-tubulin methylation in vitro. In addition, we found that the ability of LSF to facilitate this methylation is countered by factor quinolinone inhibitor 1 (FQI1), a specific small-molecule inhibitor of LSF. These findings suggest the general model that microtubule-associated proteins, including transcription factors, recruit or stimulate protein-modifying enzymes to target tubulins. Moreover, our results point to dual functions for SET8 and LSF not only in chromatin regulation but also in cytoskeletal modification.

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Kollman, Justin M., Alex Zelter, Eric G. D. Muller, Bethany Fox, Luke M. Rice, Trisha N. Davis et David A. Agard. « The Structure of the γ-Tubulin Small Complex : Implications of Its Architecture and Flexibility for Microtubule Nucleation ». Molecular Biology of the Cell 19, n^o 1 (janvier 2008) : 207–15. http://dx.doi.org/10.1091/mbc.e07-09-0879.

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The γ-tubulin small complex (γ-TuSC) is an evolutionarily conserved heterotetramer essential for microtubule nucleation. We have determined the structure of the Saccharomyces cerevisiae γ-TuSC at 25-Å resolution by electron microscopy. γ-TuSC is Y-shaped, with an elongated body connected to two arms. Gold labeling showed that the two γ-tubulins are located in lobes at the ends of the arms, and the relative orientations of the other γ-TuSC components were determined by in vivo FRET. The structures of different subpopulations of γ-TuSC indicate flexibility in the connection between a mobile arm and the rest of the complex, resulting in variation of the relative positions and orientations of the γ-tubulins. In all of the structures, the γ-tubulins are distinctly separated, a configuration incompatible with the microtubule lattice. The separation of the γ-tubulins in isolated γ-TuSC likely plays a role in suppressing its intrinsic microtubule-nucleating activity, which is relatively weak until the γ-TuSC is incorporated into higher order complexes or localized to microtubule-organizing centers. We propose that further movement of the mobile arm is required to bring the γ-tubulins together in microtubule-like interactions, and provide a template for microtubule growth.

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Million, K., J. Larcher, J. Laoukili, D. Bourguignon, F. Marano et F. Tournier. « Polyglutamylation and polyglycylation of alpha- and beta-tubulins during in vitro ciliated cell differentiation of human respiratory epithelial cells ». Journal of Cell Science 112, n^o 23 (1 décembre 1999) : 4357–66. http://dx.doi.org/10.1242/jcs.112.23.4357.

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Tubulins are the major proteins within centriolar and axonemal structures. In all cell types studied so far, numerous alpha- and beta-tubulin isoforms are generated both by expression of a multigenic family and various post-translational modifications. We have developed a primary culture of human nasal epithelial cells where the ciliated cell differentiation process has been observed and quantified. We have used this system to study several properties concerning polyglutamylation and polyglycylation of tubulin. GT335, a monoclonal antibody directed against glutamylated tubulins, stained the centriole/basal bodies and the axonemes of ciliated cells, and the centrioles of non-ciliated cells. By contrast, axonemal but not centriolar tubulins were polyglycylated. Several polyglutamylated and polyglycylated tubulin isotypes were detected by two-dimensional electrophoresis, using GT335 and a specific monoclonal antibody (TAP952) directed against short polyglycyl chains. Immunoelectron microscopy experiments revealed that polyglycylation only affected axonemal tubulin. Using the same technical approach, polyglutamylation was shown to be an early event in the centriole assembly process, as gold particles were detected in fibrogranular material corresponding to the first cytoplasmic structures involved in centriologenesis. In a functional assay, GT335 and TAP952 had a dose-dependent inhibitory effect on ciliary beat frequency. TAP952 had only a weak effect while GT335 treatment led to a total arrest of beating. These results strongly suggest that in human ciliated epithelial cells, tubulin polyglycylation has only a structural role in cilia axonemes, while polyglutamylation may have a function both in centriole assembly and in cilia activity.

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Gong, Z. Y., et B. P. Brandhorst. « Stimulation of tubulin gene transcription by deciliation of sea urchin embryos ». Molecular and Cellular Biology 7, n^o 12 (décembre 1987) : 4238–46. http://dx.doi.org/10.1128/mcb.7.12.4238-4246.1987.

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Deciliation by hypertonic shock of embryos of the sea urchin Lytechinus pictus resulted in an increase in synthesis of alpha- and beta-tubulins, the consequence of an increased concentration of RNA encoding the tubulins. RNA run-on assays in isolated nuclei indicated that this response is due to a transient increase in the rate of synthesis of tubulin RNA beginning within 5 min of deciliation. This enhancement of tubulin gene transcription also occurred in deciliated embryos treated with the microtubule-depolymerizing agent colcemid; thus the reaction to deciliation is not a response to a reduction in concentration of unpolymerized tubulin utilized for ciliogenesis. In deciliated embryos treated with colcemid, the elevated level of tubulin RNA declined rapidly, due to its destabilization by the elevated concentration of unpolymerized tubulin. The increased transcription of tubulin genes is a response to the loss of cilia, not to the hypertonic shock, and occurs even when cilium regeneration is prevented. Inhibition of protein synthesis with puromycin or emetine did not prevent the transcriptional enhancement but stabilized tubulin mRNA, resulting in increased accumulation of tubulin mRNA after deciliation.

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Gong, Z. Y., et B. P. Brandhorst. « Stimulation of tubulin gene transcription by deciliation of sea urchin embryos. » Molecular and Cellular Biology 7, n^o 12 (décembre 1987) : 4238–46. http://dx.doi.org/10.1128/mcb.7.12.4238.

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Deciliation by hypertonic shock of embryos of the sea urchin Lytechinus pictus resulted in an increase in synthesis of alpha- and beta-tubulins, the consequence of an increased concentration of RNA encoding the tubulins. RNA run-on assays in isolated nuclei indicated that this response is due to a transient increase in the rate of synthesis of tubulin RNA beginning within 5 min of deciliation. This enhancement of tubulin gene transcription also occurred in deciliated embryos treated with the microtubule-depolymerizing agent colcemid; thus the reaction to deciliation is not a response to a reduction in concentration of unpolymerized tubulin utilized for ciliogenesis. In deciliated embryos treated with colcemid, the elevated level of tubulin RNA declined rapidly, due to its destabilization by the elevated concentration of unpolymerized tubulin. The increased transcription of tubulin genes is a response to the loss of cilia, not to the hypertonic shock, and occurs even when cilium regeneration is prevented. Inhibition of protein synthesis with puromycin or emetine did not prevent the transcriptional enhancement but stabilized tubulin mRNA, resulting in increased accumulation of tubulin mRNA after deciliation.

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Gudi, Radhika, Chaozhong Zou, Jun Li et Qingshen Gao. « Centrobin–tubulin interaction is required for centriole elongation and stability ». Journal of Cell Biology 193, n^o 4 (16 mai 2011) : 711–25. http://dx.doi.org/10.1083/jcb.201006135.

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Centrobin is a daughter centriole protein that is essential for centrosome duplication. However, the molecular mechanism by which centrobin functions during centriole duplication remains undefined. In this study, we show that centrobin interacts with tubulin directly, and centrobin–tubulin interaction is pivotal for the function of centrobin during centriole duplication. We found that centrobin is recruited to the centriole biogenesis site via its interaction with tubulins during the early stage of centriole biogenesis, and its recruitment is dependent on hSAS-6 but not centrosomal P4.1–associated protein (CPAP) and CP110. The function of centrobin is also required for the elongation of centrioles, which is likely mediated by its interaction with tubulin. Furthermore, disruption of centrobin–tubulin interaction led to destabilization of existing centrioles and the preformed procentriole-like structures induced by CPAP expression, indicating that centrobin–tubulin interaction is critical for the stability of centrioles. Together, our study demonstrates that centrobin facilitates the elongation and stability of centrioles via its interaction with tubulins.

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Pratt, L. F., S. Okamura et D. W. Cleveland. « A divergent testis-specific alpha-tubulin isotype that does not contain a coded C-terminal tyrosine ». Molecular and Cellular Biology 7, n^o 1 (janvier 1987) : 552–55. http://dx.doi.org/10.1128/mcb.7.1.552-555.1987.

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On the basis of analysis of cDNA clones of alpha-tubulin RNAs expressed during spermiogenesis in chickens, we report the identification of a novel alpha-tubulin which is expressed exclusively in chicken testes. Comparison of its sequence with those previously determined not only demonstrates that the encoded polypeptide is significantly divergent from other alpha-tubulins but also supports the hypothesis that alpha-tubulin isotypes are distinguished by a carboxy-terminal variable region sequence and, to a lesser extent, by a domain near the amino terminus. Since essentially all previously known alpha-tubulins undergo a unique cycle of removal and posttranslational readdition of a tyrosine residue at the extreme carboxy terminus, the presence in this testes alpha-tubulin of a very divergent carboxy terminus that does not contain an encoded tyrosine raises the possibility that this polypeptide does not participate in the usual cycle of tyrosination/detyrosination.

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Pratt, L. F., S. Okamura et D. W. Cleveland. « A divergent testis-specific alpha-tubulin isotype that does not contain a coded C-terminal tyrosine. » Molecular and Cellular Biology 7, n^o 1 (janvier 1987) : 552–55. http://dx.doi.org/10.1128/mcb.7.1.552.

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On the basis of analysis of cDNA clones of alpha-tubulin RNAs expressed during spermiogenesis in chickens, we report the identification of a novel alpha-tubulin which is expressed exclusively in chicken testes. Comparison of its sequence with those previously determined not only demonstrates that the encoded polypeptide is significantly divergent from other alpha-tubulins but also supports the hypothesis that alpha-tubulin isotypes are distinguished by a carboxy-terminal variable region sequence and, to a lesser extent, by a domain near the amino terminus. Since essentially all previously known alpha-tubulins undergo a unique cycle of removal and posttranslational readdition of a tyrosine residue at the extreme carboxy terminus, the presence in this testes alpha-tubulin of a very divergent carboxy terminus that does not contain an encoded tyrosine raises the possibility that this polypeptide does not participate in the usual cycle of tyrosination/detyrosination.

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Pamula, Melissa C., Shih-Chieh Ti et Tarun M. Kapoor. « The structured core of human β tubulin confers isotype-specific polymerization properties ». Journal of Cell Biology 213, n^o 4 (16 mai 2016) : 425–33. http://dx.doi.org/10.1083/jcb.201603050.

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Diversity in cytoskeleton organization and function may be achieved through variations in primary sequence of tubulin isotypes. Recently, isotype functional diversity has been linked to a “tubulin code” in which the C-terminal tail, a region of substantial sequence divergence between isotypes, specifies interactions with microtubule-associated proteins. However, it is not known whether residue changes in this region alter microtubule dynamic instability. Here, we examine recombinant tubulin with human β isotype IIB and characterize polymerization dynamics. Microtubules with βIIB have catastrophe frequencies approximately threefold lower than those with isotype βIII, a suppression similar to that achieved by regulatory proteins. Further, we generate chimeric β tubulins with native tail sequences swapped between isotypes. These chimeras have catastrophe frequencies similar to that of the corresponding full-length construct with the same core sequence. Together, our data indicate that residue changes within the conserved β tubulin core are largely responsible for the observed isotype-specific changes in dynamic instability parameters and tune tubulin’s polymerization properties across a wide range.

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Ruiz, F., P. Dupuis-Williams, C. Klotz, F. Forquignon, M. Bergdoll, J. Beisson et F. Koll. « Genetic Evidence for Interaction between η- and β-Tubulins ». Eukaryotic Cell 3, n^o 1 (février 2004) : 212–20. http://dx.doi.org/10.1128/ec.3.1.212-220.2004.

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ABSTRACT The thermosensitive allelic mutations sm19-1 and sm19-2 of Paramecium tetraurelia cause defective basal body duplication: growth at the nonpermissive temperature yields smaller and smaller cells with fewer and fewer basal bodies. Complementation cloning of the SM19 gene identified a new tubulin, eta-tubulin, showing low homology with each of the other five tubulins, α to ε, characterized in P. tetraurelia. In order to analyze η-tubulin functions, we used a genetic approach to identify interacting molecules. Among a series of extragenic suppressors of the sm19-1 mutation, the su3-1 mutation was characterized as an E288K substitution in the β-PT2 gene coding for a β-tubulin, while the mutation nocr 1 conferring nocodazole resistance and localized in another β-tubulin gene, β-PT3, was shown to enhance the mutant phenotype. The interaction between η-tubulin and microtubules, revealed by genetic data, is supported by two further types of evidence: first, the mutant phenotype is rescued by taxol, which stabilizes microtubules; second, molecular modeling suggests that η-tubulin, like γ- and δ-tubulins, might be a microtubule minus-end capping molecule. The likely function of η-tubulin as part of a complex specifically involved in basal body biogenesis is discussed.

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Fackenthal, J. D., J. A. Hutchens, F. R. Turner et E. C. Raff. « Structural analysis of mutations in the Drosophila beta 2-tubulin isoform reveals regions in the beta-tubulin molecular required for general and for tissue-specific microtubule functions. » Genetics 139, n^o 1 (1 janvier 1995) : 267–86. http://dx.doi.org/10.1093/genetics/139.1.267.

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Abstract We have determined the lesions in a number of mutant alleles of beta Tub85D, the gene that encodes the testis-specific beta 2-tubulin isoform in Drosophila melanogaster. Mutations responsible for different classes of functional phenotypes are distributed throughout the beta 2-tubulin molecule. There is a telling correlation between the degree of phylogenetic conservation of the altered residues and the number of different microtubule categories disrupted by the lesions. The majority of lesions occur at positions that are evolutionarily highly conserved in all beta-tubulins; these lesions disrupt general functions common to multiple classes of microtubules. However, a single allele B2t6 contains an amino acid substitution within an internal cluster of variable amino acids that has been identified as an isotype-defining domain in vertebrate beta-tubulins. Correspondingly, B2t6 disrupts only a subset of microtubule functions, resulting in misspecification of the morphology of the doublet microtubules of the sperm tail axoneme. We previously demonstrated that beta 3, a developmentally regulated Drosophila beta-tubulin isoform, confers the same restricted morphological phenotype in a dominant way when it is coexpressed in the testis with wild-type beta 2-tubulin. We show here by complementation analysis that beta 3 and the B2t6 product disrupt a common aspect of microtubule assembly. We therefore conclude that the amino acid sequence of the beta 2-tubulin internal variable region is required for generation of correct axoneme morphology but not for general microtubule functions. As we have previously reported, the beta 2-tubulin carboxy terminal isotype-defining domain is required for suprastructural organization of the axoneme. We demonstrate here that the beta 2 variant lacking the carboxy terminus and the B2t6 variant complement each other for mild-to-moderate meiotic defects but do not complement for proper axonemal morphology. Our results are consistent with the hypothesis drawn from comparisons of vertebrate beta-tubulins that the two isotype-defining domains interact in a three-dimensional structure in wild-type beta-tubulins. We propose that the integrity of this structure in the Drosophila testis beta 2-tubulin isoform is required for proper axoneme assembly but not necessarily for general microtubule functions. On the basis of our observations we present a model for regulation of axoneme microtubule morphology as a function of tubulin assembly kinetics.

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Gu, Ying, Zhiping Deng, Alexander R. Paredez, Seth DeBolt, Zhi-Yong Wang et Chris Somerville. « Prefoldin 6 is required for normal microtubule dynamics and organization in Arabidopsis ». Proceedings of the National Academy of Sciences 105, n^o 46 (11 novembre 2008) : 18064–69. http://dx.doi.org/10.1073/pnas.0808652105.

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Newly translated tubulin molecules undergo a series of complex interactions with nascent chain-binding chaperones, including prefoldin (PFD) and chaperonin-containing TCP-1 (CCT). By screening for oryzalin hypersensitivity, we identified several mutants of Arabidopsis that have lesions in PFD subunits. The pfd6–1 mutant exhibits a range of microtubule defects, including hypersensitivity to oryzalin, defects in cell division, cortical array organization, and microtubule dynamicity. Consistent with phenotypic analysis, proteomic analysis indicates several isoforms of tubulins were reduced in pfd6–1. These results support the concept that the function of microtubules is critically dependent on the absolute amount of tubulins.

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Katz, W. S., et F. Solomon. « Diversity among beta-tubulins : a carboxy-terminal domain of yeast beta-tubulin is not essential in vivo ». Molecular and Cellular Biology 8, n^o 7 (juillet 1988) : 2730–36. http://dx.doi.org/10.1128/mcb.8.7.2730-2736.1988.

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Sequences of genes for beta-tubulins from many different organisms demonstrate that they encode highly conserved proteins but that these proteins diverge considerably at their carboxyl termini. The patterns of interspecies conservation of this diversity suggest that it may have functional significance. We have taken advantage of the properties of Saccharomyces cerevisiae to test this hypothesis in vivo. The sole beta-tubulin gene of this species is one of the most divergent of all beta-tubulins and encodes 12 amino acids which extend past the end of most other beta-tubulin molecules. We have constructed strains in which the only beta-tubulin gene is an allele lacking these 12 codons. We show here that this carboxy-terminal extension is not essential. The absence of these 12 amino acids had no effect on a number of microtubule-dependent functions, such as mitotic and meiotic division and mating. It did confer dominant supersensitivity to a microtubule-depolymerizing drug.

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Katz, W. S., et F. Solomon. « Diversity among beta-tubulins : a carboxy-terminal domain of yeast beta-tubulin is not essential in vivo. » Molecular and Cellular Biology 8, n^o 7 (juillet 1988) : 2730–36. http://dx.doi.org/10.1128/mcb.8.7.2730.

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Sequences of genes for beta-tubulins from many different organisms demonstrate that they encode highly conserved proteins but that these proteins diverge considerably at their carboxyl termini. The patterns of interspecies conservation of this diversity suggest that it may have functional significance. We have taken advantage of the properties of Saccharomyces cerevisiae to test this hypothesis in vivo. The sole beta-tubulin gene of this species is one of the most divergent of all beta-tubulins and encodes 12 amino acids which extend past the end of most other beta-tubulin molecules. We have constructed strains in which the only beta-tubulin gene is an allele lacking these 12 codons. We show here that this carboxy-terminal extension is not essential. The absence of these 12 amino acids had no effect on a number of microtubule-dependent functions, such as mitotic and meiotic division and mating. It did confer dominant supersensitivity to a microtubule-depolymerizing drug.

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Abbaali, Izra, Danny Truong, Shania Deon Day, Faliha Mushayeed, Bhargavi Ganesh, Nancy Haro-Ramirez, Juliet Isles et al. « The tubulin database : Linking mutations, modifications, ligands and local interactions ». PLOS ONE 18, n^o 12 (8 décembre 2023) : e0295279. http://dx.doi.org/10.1371/journal.pone.0295279.

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Microtubules are polymeric filaments, constructed of α-β tubulin heterodimers that underlie critical subcellular structures in eukaryotic organisms. Four homologous proteins (γ-, δ-, ε- and ζ-tubulin) additionally contribute to specialized microtubule functions. Although there is an immense volume of publicly available data pertaining to tubulins, it is difficult to assimilate all potentially relevant information across diverse organisms, isotypes, and categories of data. We previously assembled an extensive web-based catalogue of published missense mutations to tubulins with >1,500 entries that each document a specific substitution to a discrete tubulin, the species where the mutation was described and the associated phenotype with hyperlinks to the amino acid sequence and citation(s) for research. This report describes a significant update and expansion of our online resource (TubulinDB.bio.uci.edu) to nearly 18,000 entries. It now encompasses a cross-referenced catalog of post-translational modifications (PTMs) to tubulin drawn from public datasets, primary literature, and predictive algorithms. In addition, tubulin protein structures were used to define local interactions with bound ligands (GTP, GDP and diverse microtubule-targeting agents) and amino acids at the intradimer interface, within the microtubule lattice and with associated proteins. To effectively cross-reference these datasets, we established a universal tubulin numbering system to map entries into a common framework that accommodates specific insertions and deletions to tubulins. Indexing and cross-referencing permitted us to discern previously unappreciated patterns. We describe previously unlinked observations of loss of PTM sites in the context of cancer cells and tubulinopathies. Similarly, we expanded the set of clinical substitutions that may compromise MAP or microtubule-motor interactions by collecting tubulin missense mutations that alter amino acids at the interface with dynein and doublecortin. By expanding the database as a curated resource, we hope to relate model organism data to clinical findings of pathogenic tubulin variants. Ultimately, we aim to aid researchers in hypothesis generation and design of studies to dissect tubulin function.

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