SEARCH · Search PubMed

Results for “Tubulin Modulators”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 523 records · Page 29Linked to original sources

PubMed1989

Autoregulatory control of beta-tubulin mRNA stability is linked to translation elongation.

Tubulin synthesis in animal cells is controlled in part by an autoregulatory mechanism that modulates the stability of ribosome-bound tubulin mRNAs. For beta tubulin, the initial recognition event for this selective RNA instability has previously been shown to be a cotranslational binding (presumably by tubulin itself) to the nascent amino-terminal beta-tubulin tetrapeptide just after it emerges from the ribosome. Although this "autoregulation" of tubulin expression is thus obligatorily linked to the translation process, the mechanism of how a cotranslational protein-protein binding event ultimately triggers RNA degradation is unknown. Using protein synthesis inhibitors to slow and ultimately to block translation elongation, we now show that the mRNA destabilization pathway requires ongoing ribosome translocation.

Animals↗

PubMed2004

Structure of Mycobacterium tuberculosis FtsZ reveals unexpected, G protein-like conformational switches.

We report three crystal structures of the Mycobacterium tuberculosis cell division protein FtsZ, as the citrate, GDP, and GTPgammaS complexes, determined at 1.89, 2.60, and 2.08A resolution. MtbFtsZ crystallized as a tight, laterally oriented dimer distinct from the longitudinal polymer observed for alphabeta-tubulin. Mutational data on Escherichia coli FtsZ suggest that this dimer interface is important for proper protofilament and "Z-ring" assembly and function. An alpha-to-beta secondary structure conformational switch at the dimer interface is spatially analogous to, and has many of the hallmarks of, the Switch I conformational changes exhibited by G-proteins upon activation. The presence of a gamma-phosphate in the FtsZ active site modulates the conformation of the "tubulin" loop T3 (spatially analogous to the G-protein Switch II); T3 switching upon gamma-phosphate ligation is directly coupled to the alpha-to-beta switch by steric overlap. The dual conformational switches observed here for the first time in an FtsZ link GTP binding and hydrolysis to FtsZ (and tubulin) lateral assembly and Z-ring contraction, and they are suggestive of an underappreciated functional analogy between FtsZ, tubulin and G-proteins.

Bacterial Proteins↗

PubMed2003

A specific domain of Gialpha required for the transactivation of Gialpha by tubulin is implicated in the organization of cellular microtubules.

G(s)alpha, G(i)alpha(1), and G(q)alpha subunits bind tubulin with high affinity, whereas transducin (G(t)alpha) does not. The interaction between tubulin and Galpha, which also involves the direct transfer of GTP from tubulin to Galpha (transactivation), is not yet fully understood. This study, using chimeras of G(i)alpha and G(t)alpha, showed that the G(i)alpha (215-295) segment converted G(t)alpha to bind to tubulin and this chimera (chimera 1) could be transactivated by tubulin. Insertion of G(t)alpha (237-270) into chimera 1 to form chimera 2 resulted in a protein that, like G(t)alpha, did not bind tubulin. Thus, it was thought that the G(i)alpha (237-270) domain was essential to modulate the binding of G(i)alpha(1) to tubulin. Surprisingly, when domain (237-270) of G(i)alpha was replaced by G(t)alpha (237-270) to form chimera 3, the chimera bound to tubulin with a similar affinity (K(D) congruent with 120 nm) as wild-type G(i)alpha(1). However, even though chimera 3 displayed normal GTP binding, it was not transactivated by GTP-tubulin. Furthermore, when these chimeras were expressed in COS-1 cells, cellular processes in cells overexpressing G(i)alpha(1) or chimera 1 were more abundant and longer than those in native cells. Galpha was seen throughout the length of the process. Morphology of cells expressing chimera 2 was identical to controls. Consistent with the role of Chimera 3 as a "dominant negative" Galpha, cells transfected with chimera 3 had only few truncated processes. This study demonstrates that although G(i)alpha (237-270) is not obligatory for the binding of G(i)alpha to tubulin, it is crucial for the transactivation of Galpha by tubulin. These results also suggest that the transactivation of Galpha by tubulin may play an important role in modulating microtubule organization and cell morphology.

Animals↗

PubMed2000

Functional elements within the dynein microtubule-binding domain.

Dynein interacts with microtubules through an ATP-sensitive linkage mapped to a structurally complex region of the heavy chain following the fourth P-loop motif. Virtually nothing is known regarding how binding affinity is achieved and modulated during ATP hydrolysis. We have performed a detailed dissection of the microtubule contact site, using fragment expression, alanine substitution, and peptide competition. Our work identifies three clusters of amino acids important for the physical contact with microtubules; two of these fall within a region sharing sequence homology with MAP1B, the third in a region just downstream. Amino acid substitutions within any one of these regions can eliminate or weaken microtubule binding (KK3379, 80, E3385, K3387, K3397, KK3410,11, W3414, RKK3418-20, F3426, R3464, S3466, and K3467), suggesting that their activities are highly coordinated. A peptide that actively displaces MAP1B from microtubules perturbs dynein binding, supporting previous evidence for similar sites of interaction. We have also identified four amino acids whose substitutions affect release of the motor from the microtubule (E3413, R3444, E3460, and C3469). These suggest that nucleotide-sensitive affinity may be locally controlled at the site of contact. Our work is the first detailed description of dynein-tubulin interactions and provides a framework for understanding how affinity is achieved and modulated.

Adenosine Triphosphate↗

PubMed2004

Human S100B protein interacts with the Escherichia coli division protein FtsZ in a calcium-sensitive manner.

S100B is a small, dimeric EF-hand calcium-binding protein abundant in vertebrates. Upon calcium binding, S100B undergoes a conformational change allowing it to interact with a variety of target proteins, including the cytoskeletal proteins tubulin and glial fibrillary acidic protein. In both cases, S100B promotes the in vitro disassembly of these proteins in a calcium-sensitive manner. Despite this, there is little in vivo evidence for the interaction of proteins such as tubulin with S100B. To probe these interactions, we studied the expression of human S100B in Escherichia coli and its interaction with the prokaryotic ancestor of tubulin, FtsZ, the major protein involved in bacterial division. Expression of S100B protein in E. coli results in little change in FtsZ protein levels, causes a filamenting bacterial phenotype characteristic of FtsZ inhibition, and leads to missed rounds of cell division. Further, S100B localizes to positions similar to those of FtsZ in bacterial filaments: the small foci at the poles, the mid-cell positions, and between the nucleoids at regular intervals. Calcium-dependent physical interaction between S100B and FtsZ was demonstrated in vitro by affinity chromatography, and this interaction was severely inhibited by the competitor peptide TRTK-12. Together these results indicate that S100B interacts with the tubulin homologue FtsZ in vivo, modulating its activity in bacterial cell division. This approach will present an important step for the study of S100 protein interactions in vivo.

Bacterial Proteins↗

PubMed2005

The seco-taxane IDN5390 is able to target class III beta-tubulin and to overcome paclitaxel resistance.

A prominent mechanism of drug resistance to taxanes is the overexpression of class III beta-tubulin. The seco-taxane IDN5390 was chosen for its selective activity in paclitaxel-resistant cells with an overexpression of class III beta-tubulin. Moreover, the combined treatment paclitaxel/IDN5390 yielded a strong synergism, which was also evident in cell-free tubulin polymerization assays. In the presence of an anti-class III beta-tubulin as a blocking antibody, tubulin polymerization induced by paclitaxel and IDN5390 was enhanced and not affected, respectively, whereas synergism was abolished, thereby indicating that IDN5390 activity is not modulated by class III beta-tubulin levels. Such properties can be explained by taking into consideration the composition of class III beta-tubulin paclitaxel binding site; in fact, Ser277 interacting with paclitaxel C group in class I is replaced by an Arginine in class III. IDN5390 that has an open and flexible C ring and an acidic alpha-unsaturated enol-keton moiety better fits with class III beta-tubulin than paclitaxel at the binding site. Taking altogether, these findings indicate that the concomitant treatment IDN5390/paclitaxel is able to successfully target class I and III beta-tubulin and the combined use of two taxanes with diverse spectrum activity against tubulin isotypes could represent a novel approach to overcome paclitaxel resistance.

Antineoplastic Combined Chemotherapy Protocols↗

PubMed1994

Cytoskeletal modulation of the response to mechanical stimulation in human vascular endothelial cells.

Possible interactions of cytoskeletal elements with mechanically induced membrane currents and Ca2+ signals were studied in human endothelial cells by using a combined patch-clamp and Fura II technique. For mechanical stimulation, cells were exposed to hypotonic solution (HTS). The concomitant cell swelling activates a Cl- current, releases Ca2+ from intracellular stores and activates Ca2+ influx. To interfere with the cytoskeleton, cells were loaded either with the F-actin-stabilizing agent phalloidin (10 mumol/l), or the F-actin-depolymerizing substance cytochalasin B (50 mumol/l). These were administered either in the bath or the pipette solutions. The tubulin structure of the endothelial cells was modulated by taxol (50 mumol/l), which supports polymerization of tubulin, or by the depolymerizing agent colcemid (10 mumol/l) both applied to the bath. Immunofluorescence experiments show that under the chosen experimental conditions the cytoskeletal modifiers employed disintegrate the F-actin and microtubuli cytoskeleton. Neither of these cytoskeletal modifiers influenced the HTS-induced Cl- current. Ca2+ release was not affected by cytochalasin B, taxol or colcemid, but was suppressed if the cells were loaded with phalloidin. Depletion of intracellular Ca2+ stores by thapsigargin renders the intracellular [Ca2+] sensitive to the extracellular [Ca2+], which is indicative of a Ca2+ entry pathway activated by store depletion. Neither cytochalasin B nor phalloidin affected this Ca2+ entry. We conclude that F-actin turnover or depolymerization is necessary for Ca2+ release by mechanical activation. The tubulin network is not involved. The Ca2+ release- activated Ca2+ entry is not modulated by the F-actin cytoskeleton.

Actins↗

PubMed1991

Water deficit modulates gene expression in growing zones of soybean seedlings. Analysis of differentially expressed cDNAs, a new beta-tubulin gene, and expression of genes encoding cell wall proteins.

Transfer of soybean seedlings to low-water-potential vermiculite (psi w = -0.3 MPa) results in a reversible decrease in hypocotyl growth and modulation of several polysomal mRNAs (Plant Physiol 92: 205-214). We report here the isolation of two cDNA clones (pGE16 and pGE95) which correspond to genes whose mRNA levels are increased, and one cDNA clone (pGE23) which corresponds to a gene whose mRNA level is decreased in the hypocotyl zone of cell elongation by water deficit. In well-watered seedlings mRNAs hybridizing to pGE16 and pGE95 are most abundant in mature regions of the seedling, but in water-deficient seedlings mRNA levels are reduced in mature regions and enhanced in elongating regions. RNA corresponding to soybean proline-rich protein 1 (sbPRP1) shows a similar tissue distribution and response to water deficit. In contrast, in well-watered seedlings, the gene corresponding to pGE23 was highly expressed in the hypocotyl and root growing zones. Transfer of seedlings to low-water-potential vermiculite caused a rapid decrease in mRNA hybridizing to pGE23. Sequence analysis revealed that pGE23 has high homology with beta-tubulin. Water deficit also reduced the level of mRNA hybridizing to JCW1, an auxin-modulated gene, although with different kinetics. Furthermore, mRNA encoding actin, glycine-rich proteins (GRPs), and hydroxyproline-rich glycoproteins (HRGPs) were down-regulated in the hypocotyl zone of elongation of seedlings exposed to water deficit. No effect of water deficit was observed on the expression of chalcone synthase. Decreased expression of beta-tubulin, actin, JCW1, HRGP and GRP and increased expression of sbPRP1, pGE95 and pGE16 in the hypocotyl zone of cell elongation could participate in the reversible growth inhibition observed in water-deficient soybean seedlings.

Actins↗

PubMed1994

Alteration of tubulin-Gi protein interaction in rat cerebral cortex with aging.

The ability of the tubulin dimer to interact with and to modulate the Gi function inhibiting adenylyl cyclase was examined in cerebral cortex membranes from 2-month-old and 24-month-old rats. The hydrolysis-resistant GTP analogue 5'-guanylylimidodiphosphate (GppNHp)-dependent inhibition of adenylyl cyclase was significantly decreased in cerebral cortex membranes from 24-month-old rats. Tubulin, prepared from rat brains by polymerization with GppNHp, caused inhibition of adenylyl cyclase (approximately 28%) in 2-month-old rats. Tubulin-GppNHp-dependent inhibition of adenylyl cyclase in 24-month-old rats was significantly attenuated (approximately 15%). In 2-month-old rats, when tubulin, polymerized with the hydrolysis-resistant photoaffinity GTP analogue [32P]P3(4-azidoanilido)-P1-5'-GTP ([32P]AAGTP), was incubated with cerebral cortex membranes, AAGTP was transferred from tubulin to Gi alpha. Transfer of AAGTP from tubulin to Gi alpha was reduced in 24-month-old rats. Furthermore, photoaffinity labeling of [32P]AAGTP to Gi alpha in cortex membranes was significantly decreased in 24-month-old rats. No differences were observed in the amounts of Gs alpha, Gi alpha, or G beta subunits and tubulin, estimated by immunoblotting, in cortex membranes from 2-month-old and 24-month-old rats. These results suggest that the ability of tubulin to interact with Gi and thereby modulate the inhibitory regulation of adenylyl cyclase is reduced in the cerebral cortex of 24-month-old rats.

Adenylyl Cyclase Inhibitors↗

PubMed1986

Effects of forskolin on the morphology and function of the rat thyroid cell strain, FRTL-5: comparison with the effects of thyrotrophin.

The effect of diterpene forskolin, a potent stimulator of cyclic AMP (cAMP) in the rat thyroid cell strain FRTL-5, was compared with that of TSH. Forskolin stimulated both the release of cAMP into the culture medium and the accumulation of cAMP in the cytoplasm in a dose-dependent manner, within the range of 0.1-1000 mumol/l. Maximum cAMP concentrations were reached within 15 min of stimulation with forskolin. This is comparable with the effects of TSH. Forskolin also induced morphological changes in cultures of FRTL-5 cells, producing conspicuous cell retraction with arborization and numerous microvilli on the cell surface, specific reorganization of the microfilaments and modulation of the distribution of tubulin and fibronectin. Morphological changes induced by forskolin were always observed 20 to 30 min earlier, and in a higher percentage of cells, than the changes induced by TSH. Cell proliferation, however, was stimulated more effectively by TSH than by forskolin. These observations suggest that TSH might exert its effect on the morphology and growth of FRTL-5 cells, at least in part, through cAMP. The control of morphology and growth might not, however, be regulated solely by the adenylate cyclase and cAMP system.

Animals↗

PubMed2001

Differential binding regulation of microtubule-associated proteins MAP1A, MAP1B, and MAP2 by tubulin polyglutamylation.

The major neuronal post-translational modification of tubulin, polyglutamylation, can act as a molecular potentiometer to modulate microtubule-associated proteins (MAPs) binding as a function of the polyglutamyl chain length. The relative affinity of Tau, MAP2, and kinesin has been shown to be optimal for tubulin modified by approximately 3 glutamyl units. Using blot overlay assays, we have tested the ability of polyglutamylation to modulate the interaction of two other structural MAPs, MAP1A and MAP1B, with tubulin. MAP1A and MAP2 display distinct behavior in terms of tubulin binding; they do not compete with each other, even when the polyglutamyl chains of tubulin are removed, indicating that they have distinct binding sites on tubulin. Binding of MAP1A and MAP1B to tubulin is also controlled by polyglutamylation and, although the modulation of MAP1B binding resembles that of MAP2, we found that polyglutamylation can exert a different mode of regulation toward MAP1A. Interestingly, although the affinity of the other MAPs tested so far decreases sharply for tubulins carrying long polyglutamyl chains, the affinity of MAP1A for these tubulins is maintained at a significant level. This differential regulation exerted by polyglutamylation toward different MAPs might facilitate their selective recruitment into distinct microtubule populations, hence modulating their functional properties.

Animals↗

PubMed2000

Tubulin folding cofactor D is a microtubule destabilizing protein.

A rapid switch between growth and shrinkage at microtubule ends is fundamental for many cellular processes. The main structural components of microtubules, the alphabeta-tubulin heterodimers, are generated through a complex folding process where GTP hydrolysis [Fontalba et al. (1993) J. Cell Sci. 106, 627-632] and a series of molecular chaperones are required [Sternlicht et al. (1993) Proc. Natl. Acad. Sci. USA 90, 9422-9426; Campo et al. (1994) FEBS Lett. 353, 162-166; Lewis et al. (1996) J. Cell Biol. 132, 1-4; Lewis et al. (1997) Trends Cell Biol. 7, 479-484; Tian et al. (1997) J. Cell Biol. 138, 821-823]. Although the participation of the cofactor proteins along the tubulin folding route has been well established in vitro, there is also evidence that these protein cofactors might contribute to diverse microtubule processes in vivo [Schwahn et al. (1998) Nature Genet. 19, 327-332; Hirata et al. (1998) EMBO J. 17, 658-666; Fanarraga et al. (1999) Cell Motil. Cytoskel. 43, 243-254]. Microtubule dynamics, crucial during mitosis, cellular motility and intracellular transport processes, are known to be regulated by at least four known microtubule-destabilizing proteins. OP18/Stathmin and XKCM1 are microtubule catastrophe-inducing factors operating through different mechanisms [Waters and Salmon (1996) Curr. Biol. 6, 361-363; McNally (1999) Curr. Biol. 9, R274-R276]. Here we show that the tubulin folding cofactor D, although it does not co-polymerize with microtubules either in vivo or in vitro, modulates microtubule dynamics by sequestering beta-tubulin from GTP-bound alphabeta-heterodimers.

3T3 Cells↗

PubMed2006

Stat3 regulates microtubules by antagonizing the depolymerization activity of stathmin.

Stat3 is a member of the signal transducer and activator of transcription family, which is important in cytokine signaling. Gene ablation studies have revealed a requirement for Stat3 in diverse biological processes (Akira, S. 2000. Oncogene. 19: 2607-2611; Levy, D.E., and C.K. Lee. 2002. J. Clin. Invest. 109:1143-1148). Previously, the function of Stat3 had been attributed exclusively to its transcriptional activity in the nucleus. In this study, we reveal an interaction between Stat3 and the microtubule (MT)-destabilizing protein stathmin. Stathmin did not overtly affect ligand-stimulated Stat3 activation. In contrast, the expression of Stat3 is required for the stabilization of MTs and cell migration. We further demonstrate that Stat3-containing cells are resistant to the MT-destabilizing effect of stathmin overexpression. In addition, down-regulation of stathmin protein levels in Stat3-deficient cells partially reversed the MT and migration deficiencies. Recombinant Stat3 was also capable of reversing stathmin inhibition of tubulin polymerization in vitro. Our results indicate that Stat3 modulates the MT network by binding to the COOH-terminal tubulin-interacting domain of stathmin and antagonizing its MT destabilization activity.

Animals↗

PubMed1982

Modulation of some parameters of assembly of microtubules in vitro by tyrosinolation of tubulin.

Using tyrosinolated and detyrosinolated tubulins, we have compared several parameters of microtubule assembly in vitro. Rates and extents of polymerization were the same under all conditions, but microtubules assembled from detyrosinolated tubulin in the presence of crude microtubule-associated proteins (MAPs) or subsaturating MAP-2 contained a smaller proportion of the MAPs. Preliminary results indicate that this may be a function of the phosphorylation state of MAP-2. Tyrosinolated tubulin assembled into relatively shorter microtubules in the presence of saturating MAP-2. When assembly was induced with substoichiometric concentrations of taxol, in place of MAPs, the rate and extent of assembly were about twice as great with tyrosinolated tubulin.

Animals↗

PubMed2005

Hsp27 and axonal growth in adult sensory neurons in vitro.

BACKGROUND: Neurite growth can be elicited by growth factors and interactions with extracellular matrix molecules like laminin. Among the targets of the signalling pathways activated by these stimuli are cytoskeletal elements, such as actin, tubulin and neurofilaments. The cytoskeleton can also be modulated by other proteins, such as the small heat shock protein Hsp27. Hsp27 interacts with actin and tubulin in non-neuronal cells and while it has been suggested to play a role in the response of some neurons to injury, there have been no direct studies of its contribution to axonal regeneration. RESULTS: We have investigated neurite initiation and process extension using cultures of adult dorsal root ganglion (DRG) sensory neurons and a laminin stimulation paradigm. Employing confocal microscopy and biochemical analyses we have examined localization of Hsp27 at early and later stages of neurite growth. Our results show that Hsp27 is colocalized with actin and tubulin in lamellopodia, filopodia, focal contacts and mature neurites and growth cones. Disruption of the actin cytoskeleton with cytochalasin D results in aberrant neurite initiation and extension, effects which may be attributable to alterations in actin polymerization states. Inhibition of Hsp27 phosphorylation in our cultures results in an atypical growth pattern that may be attributable to an effect of pHsp27 on the stability of the actin cytoskeleton. CONCLUSION: We observed colocalization of the phosphorylated and non-phosphorylated forms of Hsp27 with actin and tubulin in both very early and later stages of neurite growth from cultured adult DRG neurons. The colocalization of Hsp27 and pHsp27 with actin in lamellopodia and focal contacts at early stages of neurite growth, and in processes, branch points and growth cones at later stages, suggests that Hsp27 may play a role in neuritogenesis and subsequent neurite extension, and potentially in the patterning of this growth. Hsp27 has been reported to play a key role in modulating actin cytoskeletal dynamics as an actin-capping protein in non-neuronal cells. Our results suggest that this may also be the case in neurons and support a role for Hsp27 in neurite outgrowth via its phosphorylation state-dependent interactions with actin.

Animals↗

PubMed1988

Tubulin post-translational modifications and the construction of microtubular organelles in Trypanosoma brucei.

We have used specific monoclonal antibodies to facilitate a study of acetylated and tyrosinated alpha-tubulin in the microtubule (MT) arrays in the Trypanosoma brucei cell. Acetylated alpha-tubulin is not solely located in the stable microtubular arrays but is present even in the ephemeral microtubules of the mitotic spindle. Moreover, there is a uniform distribution of this isoform in all arrays. Studies of flagella complexes show that acetylation is concomitant with assembly of MTs. There is no subsequent major modulation in the content of acetylated alpha-tubulin in MTs. Conversely, polymerizing flagellar MTs have a high tyrosinated alpha-tubulin content, which is subsequently reduced to a basal level at a discrete point in the cell cycle. The MTs of the intranuclear mitotic spindle appear never to contain tyrosinated alpha-tubulin, suggesting that they are actually constructed of detyrosinated alpha-tubulin or that detyrosination is extremely rapid at this time in the cell cycle. T. brucei therefore, represents a cell type with extremely active mechanisms for the post-translational modification of alpha-tubulin. Our analyses of the timing of acquisition and modulation in relation to MT construction in T. brucei, suggest that acetylation and detyrosination of alpha-tubulin are two independently regulated post-translational modifications, that are not uniquely associated with particular subsets of MTs of defined lability, position or function. Post-assembly detyrosination of alpha-tubulin may provide a mechanism whereby the cell could discriminate between new and old MTs, during construction of the cytoskeleton through the cell cycle. However, we also suggest that continuation of detyrosination, allows the cell, at cell division, to partition into daughter cells two equivalent sets of cytoskeletal MTs.

Acetylation↗

PubMed1997

Paclitaxel-resistant human ovarian cancer cells have mutant beta-tubulins that exhibit impaired paclitaxel-driven polymerization.

Acquired resistance to paclitaxel can be mediated by P-glycoprotein or by alterations involving tubulin. We report two paclitaxel-resistant sublines derived from 1A9 human ovarian carcinoma cells. Single-step paclitaxel selection with verapamil yielded two clones that are resistant to paclitaxel and collaterally sensitive to vinblastine. The resistant sublines are not paclitaxel-dependent, and resistance remained stable after 3 years of drug-free culture. All cell lines accumulate [3H]paclitaxel equally, and no MDR-1 mRNA was detected by polymerase chain reaction following reverse transcription. Total tubulin content is similar, but the polymerized fraction increased in parental but not in resistant cells following the paclitaxel addition. Purified tubulin from parental cells demonstrated paclitaxel-driven increased polymerization, in contrast to resistant cell tubulin, which did not polymerize under identical conditions. In contrast, epothilone B, an agent to which the resistant cells retained sensitivity, increased assembly. Comparable expression of beta-tubulin isotypes was found in parental and resistant cells, with predominant expression of the M40 and beta2 isotypes. Sequence analysis demonstrated acquired mutations in the M40 isotype at nucleotide 810 (T --> G; Phe270 --> Val) in 1A9PTX10 cells and nucleotide 1092 (G --> A; Ala364 --> Thr) in 1A9PTX22 cells. These results identify residues beta270 and beta364 as important modulators of paclitaxel's interaction with tubulin.

Antineoplastic Agents, Phytogenic↗

PubMed1994

Polyglutamylation of tubulin as a progressive regulator of in vitro interactions between the microtubule-associated protein Tau and tubulin.

The multiple functions of microtubules are mediated by various structural and motor microtubule-associated proteins (MAPs). To harmonize these functions in different places of a single cell, the key problem is to regulate the interactions of these proteins with microtubules. The chemical diversity of tubulin isoforms, which constitute the microtubule wall, could represent a molecular basis for this control. Using an in vitro assay of ligand blotting, we found that the microtubule-associated protein Tau interacts differentially with the diverse posttranslationally-modified isotubulins: its binding is mainly restricted to moderately-modified alpha- and beta-tubulin isoforms. We obtained evidence that the recently-discovered polyglutamylation, which consists of the sequential, posttranslational addition of one to six glutamyl units to both alpha- and beta-tubulin subunits, regulates the binding of Tau as a function of its chain length. The relative affinity of Tau, very low for unmodified tubulin, increases progressively for isotubulins carrying from one to three glutamyl units, reaches an optimal value, and then decreases progressively when the polygutamyl chain lengthens up to six residues. Our results suggest that the unmodified C-terminus of tubulin exerts a constitutive inhibition on Tau binding, probably by locking the MAP-binding site, and that this inhibition could be first released and then restored as the polyglutamyl chain grows. As the posttranslational chain does not appear to interact directly with Tau, it is thought that the growth of this chain from one to six glutamyl units causes a progressive, conformational shift in the structure of the C-terminal domain of tubulin, thus leading to the observed modulation of affinity.

Animals↗