Articles de revues : « Tubulin dimer »

1

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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2

Caplow, Michael, et Lanette Fee. « Dissociation of the Tubulin Dimer Is Extremely Slow, Thermodynamically Very Unfavorable, and Reversible in the Absence of an Energy Source ». Molecular Biology of the Cell 13, n^o 6 (juin 2002) : 2120–31. http://dx.doi.org/10.1091/mbc.e01-10-0089.

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The finding that exchange of tubulin subunits between tubulin dimers (α-β + α′β′ ↔ α′β + αβ′) does not occur in the absence of protein cofactors and GTP hydrolysis conflicts with the assumption that pure tubulin dimer and monomer are in rapid equilibrium. This assumption underlies the many physical chemical measurements of the K d for dimer dissociation. To resolve this discrepancy we used surface plasmon resonance to determine the rate constant for dimer dissociation. The half-time for dissociation was ∼9.6 h with tubulin-GTP, 2.4 h with tubulin-GDP, and 1.3 h in the absence of nucleotide. AK d equal to 10−11 M was calculated from the measured rate for dissociation and an estimated rate for association. Dimer dissociation was found to be reversible, and dimer formation does not require GTP hydrolysis or folding information from protein cofactors, because 0.2 μM tubulin-GDP incubated for 20 h was eluted as dimer when analyzed by size exclusion chromatography. Because 20 h corresponds to eight half-times for dissociation, only monomer would be present if dissociation were an irreversible reaction and if dimer formation required GTP or protein cofactors. Additional evidence for a 10−11 M K d was obtained from gel exclusion chromatography studies of 0.02–2 nM tubulin-GDP. The slow dissociation of the tubulin dimer suggests that protein tubulin cofactors function to catalyze dimer dissociation, rather than dimer assembly. Assuming N-site-GTP dissociation is from monomer, our results agree with the 16-h half-time for N-site GTP in vitro and 33 h half-life for tubulin N-site-GTP in CHO cells.

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3

Hoyle, Henry D., F. Rudolf Turner, Linda Brunick et Elizabeth C. Raff. « Tubulin Sorting during Dimerization In Vivo ». Molecular Biology of the Cell 12, n^o 7 (juillet 2001) : 2185–94. http://dx.doi.org/10.1091/mbc.12.7.2185.

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We demonstrate sorting of β-tubulins during dimerization in theDrosophila male germ line. Different β-tubulin isoforms exhibit distinct affinities for α-tubulin during dimerization. Our data suggest that differences in dimerization properties are important in determining isoform-specific microtubule functions. The differential use of β-tubulin during dimerization reveals structural parameters of the tubulin heterodimer not discernible in the resolved three-dimensional structure. We show that the variable β-tubulin carboxyl terminus, a surface feature in the heterodimer and in microtubules, and which is disordered in the crystallographic structure, is of key importance in forming a stable α-β heterodimer. If the availability of α-tubulin is limiting, α-β dimers preferentially incorporate intact β-tubulins rather than a β-tubulin missing the carboxyl terminus (β2ΔC). When α-tubulin is not limiting, β2ΔC forms stable α-β heterodimers. Once dimers are formed, no further sorting occurs during microtubule assembly: α-β2ΔC dimers are incorporated into axonemes in proportion to their contribution to the total dimer pool. Co-incorporation of β2ΔC and wild-type β2-tubulin results in nonmotile axonemes because of a disruption of the periodicity of nontubulin axonemal elements. Our data show that the β-tubulin carboxyl terminus has two distinct roles: 1) forming the α-β heterodimer, important for all microtubules and 2) providing contacts for nontubulin components required for specific microtubule structures, such as axonemes.

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Maruta, H., K. Greer et J. L. Rosenbaum. « The acetylation of alpha-tubulin and its relationship to the assembly and disassembly of microtubules. » Journal of Cell Biology 103, n^o 2 (1 août 1986) : 571–79. http://dx.doi.org/10.1083/jcb.103.2.571.

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A tight association between Chlamydomonas alpha-tubulin acetyltransferase (TAT) and flagellar axonemes, and the cytoplasmic localization of both tubulin deacetylase (TDA) and an inhibitor of tubulin acetylation have been demonstrated by the use of calf brain tubulin as substrate for these enzymes. A major axonemal TAT of 130 kD has been solubilized by high salt treatment, purified, and characterized. Using the Chlamydomonas TAT with brain tubulin as substrate, we have studied the effects of acetylation on the assembly and disassembly of microtubules in vitro. We also determined the relative rates of acetylation of tubulin dimers and polymers. The acetylation does not significantly affect the temperature-dependent polymerization or depolymerization of tubulin in vitro. Furthermore, polymerization of tubulin is not a prerequisite for the acetylation, although the polymer is a better substrate for TAT than the dimer. The acetylation is sensitive to calcium ions which completely inhibit the acetylation of both dimers and polymers of tubulin. Acetylation of the dimer is not inhibited by colchicine; the effect of colchicine on acetylation of the polymer can be explained by its depolymerizing effect on the polymer.

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5

Anders, Kirk R., et David Botstein. « Dominant-Lethal α-Tubulin Mutants Defective in Microtubule Depolymerization in Yeast ». Molecular Biology of the Cell 12, n^o 12 (décembre 2001) : 3973–86. http://dx.doi.org/10.1091/mbc.12.12.3973.

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The dynamic instability of microtubules has long been understood to depend on the hydrolysis of GTP bound to β-tubulin, an event stimulated by polymerization and necessary for depolymerization. Crystallographic studies of tubulin show that GTP is bound by β-tubulin at the longitudinal dimer-dimer interface and contacts particular α-tubulin residues in the next dimer along the protofilament. This structural arrangement suggests that these contacts could account for assembly-stimulated GTP hydrolysis. As a test of this hypothesis, we examined, in yeast cells, the effect of mutating the α-tubulin residues predicted, on structural grounds, to be involved in GTPase activation. Mutation of these residues to alanine (i.e., D252A and E255A) created poisonous α-tubulins that caused lethality even as minor components of the α-tubulin pool. When the mutant α-tubulins were expressed from the galactose-inducible promoter ofGAL1, cells rapidly acquired aberrant microtubule structures. Cytoplasmic microtubules were largely bundled, spindle assembly was inhibited, preexisting spindles failed to completely elongate, and occasional, stable microtubules were observed unattached to spindle pole bodies. Time-lapse microscopy showed that microtubule dynamics had ceased. Microtubules containing the mutant proteins did not depolymerize, even in the presence of nocodazole. These data support the view that α-tubulin is a GTPase-activating protein that acts, during microtubule polymerization, to stimulate GTP hydrolysis in β-tubulin and thereby account for the dynamic instability of microtubules.

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Montecinos-Franjola, Felipe, Peter Schuck et Dan L. Sackett. « Tubulin Dimer Reversible Dissociation ». Journal of Biological Chemistry 291, n^o 17 (2 mars 2016) : 9281–94. http://dx.doi.org/10.1074/jbc.m115.699728.

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7

Liu, Ning, Ramana Pidaparti et Xianqiao Wang. « Effect of amino acid mutations on intra-dimer tubulin–tubulin binding strength of microtubules ». Integrative Biology 9, n^o 12 (2017) : 925–33. http://dx.doi.org/10.1039/c7ib00113d.

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Binding strength inside αβ-tubulin dimers of a microtubule (MT) with atomic resolutions are of importance in determining the structural stability of the MT as well as designing self-assembled functional structures from it. Through simulations, this study proposes a new strategy to tune the binding strength inside microtubules through point mutations of amino acids on the intra-dimer interface.

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Prota, Andrea E., Maria M. Magiera, Marijn Kuijpers, Katja Bargsten, Daniel Frey, Mara Wieser, Rolf Jaussi et al. « Structural basis of tubulin tyrosination by tubulin tyrosine ligase ». Journal of Cell Biology 200, n^o 3 (28 janvier 2013) : 259–70. http://dx.doi.org/10.1083/jcb.201211017.

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Tubulin tyrosine ligase (TTL) catalyzes the post-translational retyrosination of detyrosinated α-tubulin. Despite the indispensable role of TTL in cell and organism development, its molecular mechanism of action is poorly understood. By solving crystal structures of TTL in complex with tubulin, we here demonstrate that TTL binds to the α and β subunits of tubulin and recognizes the curved conformation of the dimer. Biochemical and cellular assays revealed that specific tubulin dimer recognition controls the activity of the enzyme, and as a consequence, neuronal development. The TTL–tubulin structure further illustrates how the enzyme binds the functionally crucial C-terminal tail sequence of α-tubulin and how this interaction catalyzes the tyrosination reaction. It also reveals how TTL discriminates between α- and β-tubulin, and between different post-translationally modified forms of α-tubulin. Together, our data suggest that TTL has specifically evolved to recognize and modify tubulin, thus highlighting a fundamental role of the evolutionary conserved tubulin tyrosination cycle in regulating the microtubule cytoskeleton.

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9

Sackett, D. L., et J. Wolff. « Proteolysis of tubulin and the substructure of the tubulin dimer. » Journal of Biological Chemistry 261, n^o 19 (juillet 1986) : 9070–76. http://dx.doi.org/10.1016/s0021-9258(19)84489-7.

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10

Serrano, L., et J. Avila. « The interaction between subunits in the tubulin dimer ». Biochemical Journal 230, n^o 2 (1 septembre 1985) : 551–56. http://dx.doi.org/10.1042/bj2300551.

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Limited proteolysis and chemical cross-linking techniques have been used to study the interaction between α- and β-tubulin subunits. Trypsin digestion of tubulin dimer resulted in the cleavage of the α-subunit into two fragments, whereas chymotrypsin cleaved the β-subunit into two distinct fragments. All of these fragments have been mapped on the tubulin subunits by further proteolysis with formic acid. Cross-linking of trypsin- and chymotrypsin-cleaved subunits has been performed with two different cross-linker agents of different cross-linking distance. The addition of formaldehyde resulted in the cross-linking of the α-tubulin N-terminal fragment with β-tubulin C-terminal domain. The same result was obtained when methyl 4-mercaptobutyrimidate was used.

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11

Sackett, Dan L., David Anders Zimmerman et J. Wolff. « Tubulin dimer dissociation and proteolytic accessibility ». Biochemistry 28, n^o 6 (mars 1989) : 2662–67. http://dx.doi.org/10.1021/bi00432a045.

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12

SONCINI, MONICA, EMILIANO VOTTA, IULIANA APRODU, SØREN ENEMARK, ALBERTO REDAELLI, MARCO A. DERIU et FRANCO M. MONTEVECCHI. « MICROTUBULE-KINESIN MECHANICS BY MOLECULAR MODELING ». Biophysical Reviews and Letters 04, n^o 01n02 (avril 2009) : 45–61. http://dx.doi.org/10.1142/s1793048009000922.

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The cellular cytoskeleton contains microtubules which function both as fundamental structural elements as well as motor protein tracks. While the structural property is connected to the properties of the tubulin dimer, its interactions with surrounding dimers and the geometric organization within the microtubule, the transport track properties are related to the interactions between the tubulin dimer and kinesin. Based on the atomistic structures of kinesin and the tubulin dimer, we used molecular modeling to examine the interaction energy and force as function of a spatial distance of separation. From the results, elastic constants describing the system stiffness are obtained. By using the results related to the structure alone, a model of a 1 μm long microtubule is constructed as a network of elastic elements, and its mechanical properties were obtained via finite element method and compared to experimental results. Concerning microtubule-kinesin complex, the interaction strength during a complete cycle of ATP hydrolysis was investigated. As expected, the affinity between the proteins is modulated by the type of nucleotide occupying the nucleotide binding pocket of the motor protein. The work underscores how molecular modeling can provide fundamental protein information in terms of the relation between mechanical properties and structural changes.

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13

Wilson-Kubalek, Elizabeth M., Iain M. Cheeseman, Craig Yoshioka, Arshad Desai et Ronald A. Milligan. « Orientation and structure of the Ndc80 complex on the microtubule lattice ». Journal of Cell Biology 182, n^o 6 (15 septembre 2008) : 1055–61. http://dx.doi.org/10.1083/jcb.200804170.

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The four-subunit Ndc80 complex, comprised of Ndc80/Nuf2 and Spc24/Spc25 dimers, directly connects kinetochores to spindle microtubules. The complex is anchored to the kinetochore at the Spc24/25 end, and the Ndc80/Nuf2 dimer projects outward to bind to microtubules. Here, we use cryoelectron microscopy and helical image analysis to visualize the interaction of the Ndc80/Nuf2 dimer with microtubules. Our results, when combined with crystallography data, suggest that the globular domain of the Ndc80 subunit binds strongly at the interface between tubulin dimers and weakly at the adjacent intradimer interface along the protofilament axis. Such a binding mode, in which the Ndc80 complex interacts with sequential α/β-tubulin heterodimers, may be important for stabilizing kinetochore-bound microtubules. Additionally, we define the binding of the Ndc80 complex relative to microtubule polarity, which reveals that the microtubule interaction surface is at a considerable distance from the opposite kinetochore-anchored end; this binding geometry may facilitate polymerization and depolymerization at kinetochore-attached microtubule ends.

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Setayandeh, S. S., et A. Lohrasebi. « The effects of external electric fields of 900 MHz and 2450 MHz frequencies on αβ-tubulin dimer stabilized by paclitaxel : Molecular dynamics approach ». Journal of Theoretical and Computational Chemistry 15, n^o 02 (mars 2016) : 1650010. http://dx.doi.org/10.1142/s0219633616500103.

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Using molecular dynamics simulation method, the effects of external electric fields of 900[Formula: see text]MHz and 2450 frequencies on [Formula: see text]-tubulin dimer stabilized by paclitaxel, have been modeled. Due to this purpose, two systems, (A) [Formula: see text]-tubulin dimer and (B) [Formula: see text]-tubulin dimer stabilized by paclitaxel, were exposed to an external electric field of 0.01[Formula: see text]V/nm with frequency values of 900[Formula: see text]MHz and 2450[Formula: see text]MHz. It was found that application of these fields, which are in the range of cell phone and microwave frequencies, increased the flexibility of each system. Since paclitaxel, as chemotherapy drug, is used to increase the rigidity of dimer, application of such fields may disturb the effect of paclitaxel on the dimer. Consequently, negative side effects on the chemotherapy process may be observed.

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YANG, GANG, XIAOMIN WU, YUANGANG ZU, ZHIWEI YANG, YUJIE FU et LIJUN ZHOU. « MOLECULAR DYNAMIC SIMULATIONS ON THE FOLDING AND CONFORMATIONAL INSIGHTS OF THE TRUNCATED PEPTIDES ». Journal of Theoretical and Computational Chemistry 08, n^o 02 (avril 2009) : 317–31. http://dx.doi.org/10.1142/s0219633609004666.

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A total of 120 ns molecular dynamics simulations was used to study the folding and conformational aspects of six peptides with different lengths (Pep19–25, Pep15–25, Pep1–25, Pep15–39, Pep1–40, and Pep1–50) truncated from the αβ-tubulin dimer. These truncated peptides were found to undergo distinct structural transitions, with Pep1–25 and Pep1–50 folding into their respective stable conformations whereas on the contrary for the others. All the six truncated peptides are more or less compact than the corresponding segments in the αβ-tubulin dimer. The most striking contraction was observed in Pep1–25, which folds in a similar manner of β-hairpin. Pep1–50 has the least contraction and its folded conformation is the closest to that in the αβ-tubulin dimer. Moreover, the same conversions of β12–β23 from helices to hydrogen-bonded turns were witnessed in both Pep1–50 and the αβ-tubulin dimer. The structural instabilities of Pep19–25, Pep15–25, Pep15–39, and Pep1–40 were caused by the lack of long-distance interactions or/and the absence of key residues, with the details given in the discussions. The folding and conformational divergences of six truncated peptides were also observed in their active peptide segments ( Ap 15–25). Ap 15–25 in Pep1–50 achieves the best agreements with the αβ-tubulin dimer, implying that the local structure of Ap 15–25 in the αβ-tubulin dimer can be well reserved in Pep1–50 rather than in the other truncated peptides. The long-distance interactions, especially the key residues (e.g. β48-Arg), play a crucial role in the correct folding of Ap 15–25. The correct folding into the stable conformations is a prerequisite for the peptides to implement their catalytic actions, and therefore the present results are helpful to the future designs of active peptides.

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KARECLA, PAULA, ELIZABETH HIRST et PETER BAYLEY. « Polymorphism of tubulin assembly in vitro ». Journal of Cell Science 94, n^o 3 (1 novembre 1989) : 479–88. http://dx.doi.org/10.1242/jcs.94.3.479.

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Polymorphism in the self-assembly of tubulin dimer and microtubule protein (tubulin plus the microtubule-associated proteins) has been investigated as a function of systematic variation of solution composition (i.e. buffer ion, [glycerol] and [Mg2+]). The nature of the assembly product was examined using negative staining and thin sectioning electron microscopy. The morphology of the product of assembly of tubulin dimer was found to be strongly influenced by the concentration of glycerol and Mg2+ in Pipes and Mes buffers; the effects are less marked in phosphate buffer. Formation of bona fide microtubules in O.l M-Pipes occurs for a limited range of solution conditions (e.g. with [glycerol] <2 M and [Mg2+]<1mM). Conditions of elevated [glycerol] and [Mg2+], which enhance the rate and extent of assembly, have the adverse effect of strongly promoting the formation of polymorphic forms in addition to, and in place of, the normal microtubule morphology. In both Pipes and Mes buffers, increasing [glycerol] from 1 to 3 M favours the formation of extended multiply curved sheets, apparently made up from a basic structure with an S-like crosssection. By contrast, increasing [Mg2+] promotes the formation of junctions between microtubule walls, giving products whose cross-section shows multiple hook-like appendages, attached to closed microtubules. The assembly of tubulin dimer in a typical ‘dimer assembly buffer’ (e.g. 0.05-0.1 MMes, with 1–3.4M-glycerol and 2–7mM-Mg2+), invariably produces substantial proportions of nonmicrotubule structures such as open sheets, ribbons, and hooked structures. We conclude that the self-assembly of tubulin dimer exclusively into bona fide microtubules occurs over a very restricted range of solution conditions in the normally used Pipes- and Mes-based buffers. Deviation from these conditions readily promotes the formation of mixtures of polymorphic forms. Many buffer systems used for the assembly and disassembly of microtubules composed of tubulin dimer appear likely to promote the formation of structures related to, but significantly different from, normal microtubules. This represents a cautionary factor in the interpretation of in vitro assembly and disassembly properties of microtubules

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17

Hoogerheide, David P., Sergei Y. Noskov, Daniel Jacobs, Lucie Bergdoll, Vitalii Silin, David L. Worcester, Jeff Abramson, Hirsh Nanda, Tatiana K. Rostovtseva et Sergey M. Bezrukov. « Structural features and lipid binding domain of tubulin on biomimetic mitochondrial membranes ». Proceedings of the National Academy of Sciences 114, n^o 18 (18 avril 2017) : E3622—E3631. http://dx.doi.org/10.1073/pnas.1619806114.

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Dimeric tubulin, an abundant water-soluble cytosolic protein known primarily for its role in the cytoskeleton, is routinely found to be associated with mitochondrial outer membranes, although the structure and physiological role of mitochondria-bound tubulin are still unknown. There is also no consensus on whether tubulin is a peripheral membrane protein or is integrated into the outer mitochondrial membrane. Here the results of five independent techniques—surface plasmon resonance, electrochemical impedance spectroscopy, bilayer overtone analysis, neutron reflectometry, and molecular dynamics simulations—suggest that α-tubulin’s amphipathic helix H10 is responsible for peripheral binding of dimeric tubulin to biomimetic “mitochondrial” membranes in a manner that differentiates between the two primary lipid headgroups found in mitochondrial membranes, phosphatidylethanolamine and phosphatidylcholine. The identification of the tubulin dimer orientation and membrane-binding domain represents an essential step toward our understanding of the complex mechanisms by which tubulin interacts with integral proteins of the mitochondrial outer membrane and is important for the structure-inspired design of tubulin-targeting agents.

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Manser, E. J., et P. M. Bayley. « Tubulin-nucleotide interactions. Effects of removal of exchangeable guanine nucleotide on protein conformation and microtubule assembly ». Biochemical Journal 241, n^o 1 (1 janvier 1987) : 105–10. http://dx.doi.org/10.1042/bj2410105.

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The removal of tightly bound GDP from the exchangeable nucleotide-binding site of tubulin has been performed with alkaline phosphatase under conditions which essentially retain the assembly properties of the protein. When microtubule protein is treated with alkaline phosphatase, nucleotide is selectively removed from tubulin dimer rather than from MAP (microtubule-associated protein)-containing oligomeric species. Tubulin devoid of E-site (the exchangeable nucleotide-binding site of the tubulin dimer) nucleotide shows enhanced proteolytic susceptibility of the beta-subunit to thermolysin and decreased protein stability, consistent with nucleotide removal causing changes in protein tertiary structure. Pyrophosphate ion (3 mM) is able to promote formation of normal microtubules in the complete absence of GTP by incubation at 37 degrees C either with nucleotide-depleted microtubule protein or with nucleotide-depleted tubulin dimer to which MAPs have been added. The resulting microtubules contain up to 80% of tubulin lacking E-site nucleotide. In addition to its effects on nucleation, pyrophosphate competes weakly with GDP bound at the E-site. It is deduced that binding of pyrophosphate at a vacant E-site can promote microtubule assembly. The minimum structural requirement for ligands to induce tubulin assembly apparently involves charge neutralization at the E-site by bidentate ligation, which stabilizes protein domains in a favourable orientation for promoting the supramolecular protein-protein interactions involved in microtubule formation.

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Naghsh, Farnoush, Majid Monajjemi et Karim Zare. « Study of dynamic reaction of tubulins in microtubules. A qm/mm simulation ». Nexo Revista Científica 33, n^o 01 (20 juillet 2020) : 22–35. http://dx.doi.org/10.5377/nexo.v33i01.10043.

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In this model one-dimensional microtubule is fixed at one of the two and simulated while the opposite end is allowed for growing in random situation. By this study at each step one tubulin has been added to the length for growing microtubule length. Computationally this can be done through generating a uniform random number between (0, 1). Microtubules are demonstrated as straight macromolecules consist of the linear chains of tubulin subunits in the length. QM/MM simulation has been applied to study dynamic instability of the microtubule length. It has been calculated a correct dimension around 10-6 meter of microtubules length consist of around 1650 tubulin dimers. Microtubule growth rate is related to the soluble tubulin dimer concentration and for all results shown here, simulation of any single condition was run 5–10 times.

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Szyk, Agnieszka, Alexandra Deaconescu, Grzegorz Piszczek et Antonina Roll-Mecak. « Tubulin tyrosine ligase - structural and functional studies ». Acta Crystallographica Section A Foundations and Advances 70, a1 (5 août 2014) : C479. http://dx.doi.org/10.1107/s2053273314095205.

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Microtubules are polymers essential for cell morphogenesis, cell division and intracellular transport. This polymer's basic building block is the α/β tubulin heterodimer, which associates head-to-tail and laterally to form the microtubule. Tubulin is subject to diverse, abundant and evolutionarily conserved post-translational modifications that mark subpopulations of microtubules. The highest density and variety of post-translational modifications are found in neurons or cilia. Not surprisingly, tubulin modification enzymes have been linked to human diseases including cancers and neurodegenerative disorders. We will present our recent work using a combination of X-ray crystallography, small angle X-ray scattering and functional assays to investigate the mechanism of tubulin tyrosine ligase (TTL). TTL catalyzes the ATP-dependent post-translational addition of a tyrosine to the C-terminal end of detyrosinated α-tubulin. The detyrosination/tyrosination cycle regulates recruitment of motors and proteins that track with the growing end of the microtubule. TTL function is essential for neuronal development and reduction in TTL levels is strongly associated with aggressive tumors resistant to chemotherapy. Our first X-ray crystal structure of TTL, defines the structural fold of the TTL-like family of tubulin-modifying enzymes. We show that TTL recognizes tubulin via a dual strategy: it engages the tubulin tail through low-affinity, high-specificity interactions through a conserved positively charged surface, and co-opts what is otherwise a homo-oligomerization interface in structurally related enzymes to form a tight hetero-oligomeric complex with tubulin. TTL forms an elongated complex with the tubulin dimer and prevents incorporation of the dimer into microtubules by capping the tubulin polymerization interface. Interestingly, TTL and stathmin, a ubiquitously expressed tubulin sequestering protein, compete for tubulin binding in vitro and stathmin inhibits tubulin tyrosination. These results suggest that TTL and stathmin have either a partially overlapping footprint on the tubulin dimer or that stathmin induces a tubulin conformation incompatible with stable TTL binding.

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Ichikawa, Muneyoshi, Ahmad Abdelzaher Zaki Khalifa, Shintaroh Kubo, Daniel Dai, Kaustuv Basu, Mohammad Amin Faghfor Maghrebi, Javier Vargas et Khanh Huy Bui. « Tubulin lattice in cilia is in a stressed form regulated by microtubule inner proteins ». Proceedings of the National Academy of Sciences 116, n^o 40 (16 septembre 2019) : 19930–38. http://dx.doi.org/10.1073/pnas.1911119116.

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Cilia, the hair-like protrusions that beat at high frequencies to propel a cell or move fluid around are composed of radially bundled doublet microtubules. In this study, we present a near-atomic resolution map of the Tetrahymena doublet microtubule by cryoelectron microscopy. The map demonstrates that the network of microtubule inner proteins weaves into the tubulin lattice and forms an inner sheath. From mass spectrometry data and de novo modeling, we identified Rib43a proteins as the filamentous microtubule inner proteins in the protofilament ribbon region. The Rib43a–tubulin interaction leads to an elongated tubulin dimer distance every 2 dimers. In addition, the tubulin lattice structure with missing microtubule inner proteins (MIPs) by sarkosyl treatment shows significant longitudinal compaction and lateral angle change between protofilaments. These results are evidence that the MIPs directly affect and stabilize the tubulin lattice. It suggests that the doublet microtubule is an intrinsically stressed filament and that this stress could be manipulated in the regulation of ciliary waveforms.

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Bras, Wim, James Torbet, Gregory P. Diakun, Geert L. J. A. Rikken et J. Fernando Diaz. « The Diamagnetic Susceptibility of the Tubulin Dimer ». Journal of Biophysics 2014 (18 février 2014) : 1–5. http://dx.doi.org/10.1155/2014/985082.

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An approximate value of the diamagnetic anisotropy of the tubulin dimer, Δχdimer, has been determined assuming axial symmetry and that only the α-helices and β-sheets contribute to the anisotropy. Two approaches have been utilized: (a) using the value for the Δχα for an α-helical peptide bond given by Pauling (1979) and (b) using the previously determined anisotropy of fibrinogen as a calibration standard. The Δχdimer≈4×10-27 JT−2 obtained from these measurements are similar to within 20%. Although Cotton-Mouton measurements alone cannot be used to estimate Δχ directly, the value we measured, CMdimer=1.41±0.03×10-8 T−2cm2mg−1, is consistent with the above estimate for Δχdimer. The method utilized for the determination of the tubulin dimer diamagnetic susceptibility is applicable to other proteins and macromolecular assemblies as well.

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Mejillano, Magdalena R., et Richard H. Himes. « Tubulin dimer dissociation detected by fluorescence anisotropy ». Biochemistry 28, n^o 15 (25 juillet 1989) : 6518–24. http://dx.doi.org/10.1021/bi00441a053.

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Song, Y. H., et E. Mandelkow. « The anatomy of flagellar microtubules : polarity, seam, junctions, and lattice. » Journal of Cell Biology 128, n^o 1 (1 janvier 1995) : 81–94. http://dx.doi.org/10.1083/jcb.128.1.81.

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Although the overall structures of flagellar and cytoplasmic microtubules are understood, many details have remained a matter of debate. In particular, studies of the arrangement of tubulin subunits have been hampered by the low contrast of the tubulin subunits. This problem can now be addressed by the kinesin decoration technique. We have shown previously that the recombinant kinesin head domain binds to beta-tubulin, thus enhancing the contrast between alpha- and beta-tubulin in the electron microscope; this allows one to study the arrangement of tubulin dimers. Here we describe the lattices of the four different types of microtubules in eukaryotic flagellar axonemes (outer doublet A and B, central pair C1 and C2). They could all be labeled with kinesin head with an 8-nm axial periodicity (the tubulin dimer repeat), and all of them showed the B-surface lattice. This lattice is characterized by a 0.92-nm stagger between adjacent protofilaments. The B-lattice was observed on the axonemal microtubules as well as on extensions made by polymerizing porcine brain tubulin onto axonemal microtubules in the proximal and distal directions. This emphasizes that axonemal microtubules serve as high fidelity templates for seeding microtubules. The presence of a B-lattice implies that there must be a helical discontinuity ("seam") in the wall. This discontinuity is now placed near protofilaments A1 and A2 of the A-tubule, close to the inner junction between A- and B-microtubules. The two junctions differ in structure: the protofilaments of the inner junction (A1-B10) are staggered roughly by half a dimer, those of the outer junction (A10-B1) are roughly in register. Of the two junctions the inner one appears to have the stronger bonds, whereas the outer one is more labile and opens up easily, generating "composite sheets" with chevron patterns from which the polarity can be deduced (arrow in the plus direction). Decorated microtubules have a clear polarity. We find that all flagellar microtubules have the same polarities. The orientation of the dimers is such that the plus end terminates with a crown of alpha subunits, the minus end terminates with beta subunits which thus could be in contact with gamma-tubulin at the nucleation centers.

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Panda, Dulal, Siddhartha Roy et B. Bhattacharyya. « Reversible dimer dissociation of tubulin S and tubulin detected by fluorescence anisotropy ». Biochemistry 31, n^o 40 (octobre 1992) : 9709–16. http://dx.doi.org/10.1021/bi00155a026.

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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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Al-Bassam, Jawdat, Hwajin Kim, Ignacio Flor-Parra, Neeraj Lal, Hamida Velji et Fred Chang. « Fission yeast Alp14 is a dose-dependent plus end–tracking microtubule polymerase ». Molecular Biology of the Cell 23, n^o 15 (août 2012) : 2878–90. http://dx.doi.org/10.1091/mbc.e12-03-0205.

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XMAP215/Dis1 proteins are conserved tubulin-binding TOG-domain proteins that regulate microtubule (MT) plus-end dynamics. Here we show that Alp14, a XMAP215 orthologue in fission yeast, Schizosaccharomyces pombe, has properties of a MT polymerase. In vivo, Alp14 localizes to growing MT plus ends in a manner independent of Mal3 (EB1). alp14-null mutants display short interphase MTs with twofold slower assembly rate and frequent pauses. Alp14 is a homodimer that binds a single tubulin dimer. In vitro, purified Alp14 molecules track growing MT plus ends and accelerate MT assembly threefold. TOG-domain mutants demonstrate that tubulin binding is critical for function and plus end localization. Overexpression of Alp14 or only its TOG domains causes complete MT loss in vivo, and high Alp14 concentration inhibits MT assembly in vitro. These inhibitory effects may arise from Alp14 sequestration of tubulin and effects on the MT. Our studies suggest that Alp14 regulates the polymerization state of tubulin by cycling between a tubulin dimer–bound cytoplasmic state and a MT polymerase state that promotes rapid MT assembly.

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Hoenger, A., S. Sack, M. Thormählen, A. Marx, J. Müller, H. Gross et E. Mandelkow. « Image Reconstructions of Microtubules Decorated with Monomeric and Dimeric Kinesins : Comparison with X-Ray Structure and Implications for Motility ». Journal of Cell Biology 141, n^o 2 (20 avril 1998) : 419–30. http://dx.doi.org/10.1083/jcb.141.2.419.

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We have decorated microtubules with monomeric and dimeric kinesin constructs, studied their structure by cryoelectron microscopy and three-dimensional image reconstruction, and compared the results with the x-ray crystal structure of monomeric and dimeric kinesin. A monomeric kinesin construct (rK354, containing only a short neck helix insufficient for coiled-coil formation) decorates microtubules with a stoichiometry of one kinesin head per tubulin subunit (α–β-heterodimer). The orientation of the kinesin head (an anterograde motor) on the microtubule surface is similar to that of ncd (a retrograde motor). A longer kinesin construct (rK379) forms a dimer because of the longer neck helix forming a coiled-coil. Unexpectedly, this construct also decorates the microtubule with a stoichiometry of one head per tubulin subunit, and the orientation is similar to that of the monomeric construct. This means that the interaction with microtubules causes the two heads of a kinesin dimer to separate sufficiently so that they can bind to two different tubulin subunits. This result is in contrast to recent models and can be explained by assuming that the tubulin–kinesin interaction is antagonistic to the coiled-coil interaction within a kinesin dimer.

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Roll-Mecak, Antonina, Agnieszka Szyk et Vasilisa Kormendi. « Microtubule chemical complexity : mechanism of tubulin modification enzymes ». Acta Crystallographica Section A Foundations and Advances 70, a1 (5 août 2014) : C1286. http://dx.doi.org/10.1107/s2053273314087130.

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Tubulin is subject to an abundant and diverse set of post-translational modifications that include phosphorylation, acetylation, poly-glutamylation, poly-glycylation and tyrosination. The highest density and variety of post-translational modifications are found in especially complex microtubule arrays like those of neurons or cilia. Not surprisingly, tubulin modification enzymes have been linked to human diseases including cancers and neurodegenerative disorders. I will present recent data from my lab on the mechanism of action of two tubulin modification enzymes that illustrate two divergent paradigms of tubulin recognition. Tubulin tyrosine ligase (TTL) adds a C-terminal Tyr to the exposed C-terminus of alpha-tubulin as part of a tyrosination/detyrosination cycle present in most eukaryotic cells. We solved the first crystal structure of tubulin tyrosine ligase that revealed how the TTL scaffold supported the expansion of the repertory of tubulin post-translational modification enzymes of the TTL like family that recognize either alpha- or beta-tubulin C-terminal tails. In addition to modifying tubulin, TTL also prevents tubulin from incorporating into microtubules by recognizing a tubulin dimer interface that would otherwise be involved in microtubule lattice interactions. I will also present recent work from my group on the structure and mechanism of action of tubulin acetyltransferase (TAT). TAT acetylates Lys-40 on alpha-tubulin in the microtubule lumen. We solved the 2.7Å structure of TAT bound to its ac-coA substrate as well as the 2.45Å structure of a catalytic inactive TAT mutant that reveals a domain swapped dimer in which the functionally essential N-terminus shows evidence of unprecedented structural plasticity. Implications for catalysis and microtubule stimulation of TAT activity will be discussed.

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Sackett, Dan L., et Roland E. Lippoldt. « Thermodynamics of reversible monomer-dimer association of tubulin ». Biochemistry 30, n^o 14 (avril 1991) : 3511–17. http://dx.doi.org/10.1021/bi00228a023.

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Gache, Vincent, Mathilde Louwagie, Jérôme Garin, Nicolas Caudron, Laurence Lafanechere et Odile Valiron. « Identification of proteins binding the native tubulin dimer ». Biochemical and Biophysical Research Communications 327, n^o 1 (février 2005) : 35–42. http://dx.doi.org/10.1016/j.bbrc.2004.11.138.

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Jurášek, Michal, Markéta Černohorská, Jiří Řehulka, Vojtěch Spiwok, Tetyana Sulimenko, Eduarda Dráberová, Maria Darmostuk et al. « Estradiol dimer inhibits tubulin polymerization and microtubule dynamics ». Journal of Steroid Biochemistry and Molecular Biology 183 (octobre 2018) : 68–79. http://dx.doi.org/10.1016/j.jsbmb.2018.05.008.

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Zabala, Juan C., et Nicholas J. Cowan. « Tubulin dimer formation via the release of ?- and ?-tubulin monomers from multimolecular complexes ». Cell Motility and the Cytoskeleton 23, n^o 3 (1992) : 222–30. http://dx.doi.org/10.1002/cm.970230306.

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NOEL, CHRISTOPHE, DELPHINE GERBOD, NAOMI M. FAST, RENE WINTJENS, PILAR DELGADO-VISCOGLIOSI, W. FORD DOOLITTLE et ERIC VISCOGLIOSI. « Tubulins in Trichomonas vaginalis : Molecular Characterization of alpha-Tubulin Genes, Posttranslational Modifications, and Homology Modeling of the Tubulin Dimer ». Journal of Eukaryotic Microbiology 48, n^o 6 (novembre 2001) : 647–54. http://dx.doi.org/10.1111/j.1550-7408.2001.tb00204.x.

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Montecinos-Franjola, Felipe, Peter Schuck et Dan L. Sackett. « Tubulin Monomer-Monomer Association is Less Influenced by the Solvent than Dimer-Dimer Association : Structure and Function of Tubulin Interaction Interfaces ». Biophysical Journal 110, n^o 3 (février 2016) : 26a—27a. http://dx.doi.org/10.1016/j.bpj.2015.11.207.

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Neumann, Tobias, Steffen O. Kirschstein, Juan A. Camacho Gomez, Leonhard Kittler et Eberhard Unger. « Determination of the Net Exchange Rate of Tubulin Dimer in Steady-State Microtubules by Fluorescence Correlation Spectroscopy ». Biological Chemistry 382, n^o 3 (21 mars 2001) : 387–91. http://dx.doi.org/10.1515/bc.2001.047.

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Abstract The microtubule cytoskeleton plays an important role in eukaryotic cells, e. g., in cell movement or morphogenesis. Microtubules, formed by assembly of tubulin dimers, are dynamic polymers changing randomly between periods of growing and shortening, a property known as dynamic instability. Another process characterizing the dynamic behaviour is the socalled treadmilling due to different binding constants of tubulin at both microtubule ends. In this study, we used tetramethylrhodamine (TMR)labeled tubulin added to microtubule suspensions to determine the net exchange rate (NER) of tubulin dimers by fluorescence correlation spectroscopy (FCS) as a measure for microtubule dynamics. This approach, which seems to be suitable as screening system to detect compounds influencing the NER of tubulin dimers into microtubules at steadystate, showed that taxol, nocodazole, colchicine, and vinblastine affect microtubule dynamics at concentrations as low as 10[-9] 10[-10] M.

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Watts, Norman R., Naiqian Cheng, Wendy West, Alasdair C. Steven et Dan L. Sackett. « The Cryptophycin−Tubulin Ring Structure Indicates Two Points of Curvature in the Tubulin Dimer† ». Biochemistry 41, n^o 42 (octobre 2002) : 12662–69. http://dx.doi.org/10.1021/bi020430x.

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Carney, Daniel W., John C. Lukesh, Daniel M. Brody, Manuela M. Brütsch et Dale L. Boger. « Ultrapotent vinblastines in which added molecular complexity further disrupts the target tubulin dimer–dimer interface ». Proceedings of the National Academy of Sciences 113, n^o 35 (10 août 2016) : 9691–98. http://dx.doi.org/10.1073/pnas.1611405113.

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Approaches to improving the biological properties of natural products typically strive to modify their structures to identify the essential pharmacophore, or make functional group changes to improve biological target affinity or functional activity, change physical properties, enhance stability, or introduce conformational constraints. Aside from accessible semisynthetic modifications of existing functional groups, rarely does one consider using chemical synthesis to add molecular complexity to the natural product. In part, this may be attributed to the added challenge intrinsic in the synthesis of an even more complex compound. Herein, we report synthetically derived, structurally more complex vinblastines inaccessible from the natural product itself that are a stunning 100-fold more active (IC50 values, 50–75 pM vs. 7 nM; HCT116), and that are now accessible because of advances in the total synthesis of the natural product. The newly discovered ultrapotent vinblastines, which may look highly unusual upon first inspection, bind tubulin with much higher affinity and likely further disrupt the tubulin head-to-tail α/β dimer–dimer interaction by virtue of the strategic placement of an added conformationally well-defined, rigid, and extended C20′ urea along the adjacent continuing protein–protein interface. In this case, the added molecular complexity was used to markedly enhance target binding and functional biological activity (100-fold), and likely represents a general approach to improving the properties of other natural products targeting a protein–protein interaction.

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Sakakibara, H., et H. Nakayama. « Translocation of microtubules caused by the alphabeta, beta and gamma outer arm dynein subparticles of Chlamydomonas ». Journal of Cell Science 111, n^o 9 (1 mai 1998) : 1155–64. http://dx.doi.org/10.1242/jcs.111.9.1155.

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Three kinds of subparticles of Chlamydomonas outer-arm dynein containing the alphabeta, beta and gamma heavy chains were isolated and assayed for their activities to translocate microtubules in vitro. All of them had activities to form bundles of microtubules in solution in an ATP-dependent manner and, when adsorbed on an appropriate glass surface, translocated microtubules. The alphabeta subparticle readily translocated microtubules on a silicone-coated glass surface with a velocity of 4.6 micron/second at 1 mM ATP. The beta subparticle translocated microtubules after it had been preincubated with tubulin dimer and when the Brownian movement of microtubules was suppressed by addition of methylcellulose. The velocity was on average 0.7 micron/second. The gamma subparticle translocated microtubules after being preincubated with tubulin dimer and adsorbed onto a silicone-coated glass surface. The velocity was about 3.8 micron/second. The tubulin dimer appeared to facilitate in vitro motility by blocking the ATP-insensitive binding of dynein subparticles to microtubule. The alphabeta, beta and gamma subparticles were thus found to have different properties as motor proteins. In addition, these subparticles showed different dependencies upon the potassium acetate concentration. Hence the outer-arm dynein of Chlamydomonas is a complex of motor proteins with different properties.

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CAMPBELL, ROBERT D. J. « A COMPUTER MODEL OF THE FERROELECTRIC PROPERTIES OF MICROTUBULES ». International Journal of Modern Physics B 18, n^o 02 (20 janvier 2004) : 253–74. http://dx.doi.org/10.1142/s0217979204023854.

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The tubulin dimers of microtubules are arranged in a crystalline lattice which is wrapped to form a long cylinder. Two different arrangements of monomers within the lattice have been postulated: the A-lattice and the B-lattice. Previous studies have assumed that both lattice types are hexagonal with each dimer surrounded by six nearest-neighbors. Based on recent biochemical studies I argue that both lattice types can also be formed with each dimer having four nearest-neighbors. This has important consequences for the overall behavior of the model. It is generally assumed that tubulin dimers possess a mobile electric dipole which can exist in one of two discrete Ising spin states: -1 (down) or +1 (up). The average of all these states within a microtubule is the mean polarization and is a measure of the dipole ordering within the lattice. Microtubule models with six nearest-neighbors behave like models of ferroelectric substances: at low temperatures the lattice is highly ordered with most (if not all) dipoles pointing in the same direction, but as the temperature increases, the degree of ordering decreases due to random thermal flipping of the dipoles. The mean polarization is particularly erratic at physiological temperatures. In contrast, when the microtubule lattice is modeled with four nearest-neighbors, the mean lattice polarization is quite stable and remains close to zero over a wide temperature range that includes 37°C (310K). This raises new questions about the biophysical role of microtubules.

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Nogales, Eva, Sharon G. Wolf et Kenneth H. Downing. « Structure of the αβ tubulin dimer by electron crystallography ». Nature 391, n^o 6663 (8 janvier 1998) : 199–203. http://dx.doi.org/10.1038/34465.

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Szymanski, Dan. « Tubulin Folding Cofactors : Half a Dozen for a Dimer ». Current Biology 12, n^o 22 (novembre 2002) : R767—R769. http://dx.doi.org/10.1016/s0960-9822(02)01288-5.

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Krebs, Angelika, Kenneth N. Goldie et Andreas Hoenger. « Identification of the αβ-tubulin dimer in intact microtubules ». Microscopy and Microanalysis 9, S03 (septembre 2003) : 394–95. http://dx.doi.org/10.1017/s1431927603033026.

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de la Torre, Jose Garcı́a, et Jose M. Andreu. « Appendix : Hydrodynamic Analysis of Tubulin Dimer and Double Rings ». Journal of Molecular Biology 238, n^o 2 (avril 1994) : 223–25. http://dx.doi.org/10.1006/jmbi.1994.1283.

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Jessus, C., C. Thibier et R. Ozon. « Levels of microtubules during the meiotic maturation of the Xenopus oocyte ». Journal of Cell Science 87, n^o 5 (1 juin 1987) : 705–12. http://dx.doi.org/10.1242/jcs.87.5.705.

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The total level of tubulin and the ratio of polymeric tubulin to tubulin dimer were measured by a colchicine filter-binding assay during meiotic maturation of the Xenopus oocyte. Although the total level of tubulin remains unchanged (0.12 +/− 0.03 micrograms/oocyte), the level of polymeric tubulin decreases during maturation (25% in prophase oocytes versus 20% in metaphase oocytes). The percentage of polymerized tubulin was estimated after drug (nocodazole and taxol) treatments and cold treatment in prophase and progesterone-matured oocytes; in all cases the microtubules present in mature oocyte are less stable than prophase microtubules. The presence of the nucleus modifies neither the level nor the stability of prophase microtubules. Our quantitative results as well as cytological arguments suggest that full-grown Xenopus oocytes may contain a cortical microtubular array.

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Shigematsu, Hideki, Tsuyoshi Imasaki, Chihiro Doki, Takuya Sumi, Mari Aoki, Tomomi Uchikubo-Kamo, Ayako Sakamoto, Kiyotaka Tokuraku, Mikako Shirouzu et Ryo Nitta. « Structural insight into microtubule stabilization and kinesin inhibition by Tau family MAPs ». Journal of Cell Biology 217, n^o 12 (1 octobre 2018) : 4155–63. http://dx.doi.org/10.1083/jcb.201711182.

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The Tau family microtubule-associated proteins (MAPs) promote microtubule stabilization and regulate microtubule-based motility. They share the C-terminal microtubule-binding domain, which includes three to five tubulin-binding repeats. Different numbers of repeats formed by alternative splicing have distinct effects on the activities of these proteins, and the distribution of these variants regulates fundamental physiological phenomena in cells. In this study, using cryo-EM, we visualized the MAP4 microtubule complex with the molecular motor kinesin-1. MAP4 bound to the C-terminal domains of tubulins along the protofilaments stabilizes the longitudinal contacts of the microtubule. The strongest bond of MAP4 was found around the intertubulin–dimer interface such that MAP4 coexists on the microtubule with kinesin-1 bound to the intratubulin–dimer interface as well. MAP4, consisting of five repeats, further folds and accumulates above the intertubulin–dimer interface, interfering with kinesin-1 movement. Therefore, these cryo-EM studies reveal new insight into the structural basis of microtubule stabilization and inhibition of kinesin motility by the Tau family MAPs.

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Contini, Alessandro, Graziella Cappelletti, Daniele Cartelli, Gabriele Fontana et Maria Luisa Gelmi. « Molecular dynamics and tubulin polymerization kinetics study on 1,14-heterofused taxanes : evidence of stabilization of the tubulin head-to-tail dimer–dimer interaction ». Molecular BioSystems 8, n^o 12 (2012) : 3254. http://dx.doi.org/10.1039/c2mb25326g.

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Mandelkow, E. M., R. Schultheiss, R. Rapp, M. Müller et E. Mandelkow. « On the surface lattice of microtubules : helix starts, protofilament number, seam, and handedness. » Journal of Cell Biology 102, n^o 3 (1 mars 1986) : 1067–73. http://dx.doi.org/10.1083/jcb.102.3.1067.

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The tubulin monomers of brain microtubules reassembled in vitro are arranged on a 3-start helix, irrespective of whether the number of protofilaments is 13 or 14. The dimer packing is that of the B-lattice described for flagellar microtubules. This implies that the tubulin core of microtubules contains at least one helical discontinuity. Neither 5-start nor 8-start helices have a physical significance and thus cannot be implicated in models of microtubule elongation, but the structure is compatible with elongation of protofilaments by dimers or protofilamentous oligomers. The inner and outer surfaces of the microtubule wall can be visualized by propane jet freezing, freeze fracturing, and metal replication, at a resolution of at least 4 nm. The 3-start helix is left-handed, in contrast to a previous study based on negative staining and shadowing. The reasons for this discrepancy are discussed.

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Shikinaka, Kazuhiro, Saori Mori, Kiyotaka Shigehara et Hiroyasu Masunaga. « Helical alignment inversion of microtubules in accordance with a structural change in their lattice ». Soft Matter 11, n^o 19 (2015) : 3869–74. http://dx.doi.org/10.1039/c5sm00488h.

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Finely-regulated giant helical alignments of microtubules with centimeter order according to their lattice structure form over a temperature gradient during anisotropic spiral propagation via tubulin dimer addition in a capillary cell.

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Vassilev, A., M. Kimble, C. D. Silflow, M. LaVoie et R. Kuriyama. « Identification of intrinsic dimer and overexpressed monomeric forms of gamma-tubulin in Sf9 cells infected with baculovirus containing the Chlamydomonas gamma-tubulin sequence ». Journal of Cell Science 108, n^o 3 (1 mars 1995) : 1083–92. http://dx.doi.org/10.1242/jcs.108.3.1083.

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A new member of the tubulin superfamily, gamma-tubulin, is localized at microtubule-organizing centers (MTOCs) in a variety of organisms. Chlamydomonas cDNA coding for the full-length sequence of gamma-tubulin was expressed in insect ovarian Sf9 cells using the baculovirus expression system. Approximately half of the induced 52 kDa gamma-tubulin was recovered in the supernatant after centrifugation of Sf9 cell lysates at 18,000 g for 15 minutes. When the cell supernatant was analyzed by FPLC on a Superdex 200 sizing column, Chlamydomonas gamma-tubulin separated into two major peaks. The lagging peak contained a monomeric form of gamma-tubulin with a sedimentation coefficient of 2.5 S, which interacted with the Superdex column in a salt-dependent manner. The leading peak, with an apparent molecular mass of 900 kDa, corresponded to a molecular chaperonin complex, and TCP1 chaperonin released folded gamma-tubulin polypeptide from the complex in the presence of MgATP. The released gamma-tubulin monomers were capable of binding to microtubules in vitro and biochemical quantities of active monomers were further purified using a combination of size-exclusion and ion-exchange column chromatography. The endogenous Sf9 cell gamma-tubulin migrated faster than Chlamydomonas gamma-tubulin with an apparent molecular mass of 49 kDa on gels. Analyses on gel filtration and sucrose density gradient centrifugation showed that, while overexpressed Chlamydomonas gamma-tubulin was present in a monomeric form, endogenous gamma-tubulin from Sf9 and HeLa cells exists as a dimer. These results may suggest the possibility that gamma-tubulin could form a heterodimer with hitherto unknown molecule(s).

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