scholarly journals Evidence for conformational change-induced hydrolysis of β-tubulin-GTP

2020 ◽  
Author(s):  
Mohammadjavad Paydar ◽  
Benjamin H. Kwok
Keyword(s):  
Conformational Change ◽  
Intracellular Transport ◽  
Chemical Agent ◽  
Microtubule Depolymerization ◽  
Gtp Hydrolysis ◽  
Structural Framework ◽  
Microtubule Polymerization ◽  
Average Size ◽  
Cell Shape Formation ◽  
Β Tubulin

ABSTRACTMicrotubules, protein polymers of α/β-tubulin dimers, form the structural framework for many essential cellular processes including cell shape formation, intracellular transport, and segregation of chromosomes during cell division. It is known that tubulin-GTP hydrolysis is closely associated with microtubule polymerization dynamics. However, the precise roles of GTP hydrolysis in tubulin polymerization and microtubule depolymerization, and how it is initiated are still not clearly defined. We report here that tubulin-GTP hydrolysis can be triggered by conformational change induced by the depolymerizing kinesin-13 proteins or by the stabilizing chemical agent paclitaxel. We provide biochemical evidence that conformational change precedes tubulin-GTP hydrolysis, confirming this process is mechanically driven and structurally directional. Furthermore, we quantitatively measure the average size of the presumptive stabilizing “GTP cap” at growing microtubule ends. Together, our findings provide the molecular basis for tubulin-GTP hydrolysis and its role in microtubule polymerization and depolymerization.

scholarly journals Dominant-Lethal α-Tubulin Mutants Defective in Microtubule Depolymerization in Yeast

2001 ◽  
Vol 12 (12) ◽  
pp. 3973-3986 ◽  
Author(s):  
Kirk R. Anders ◽  
David Botstein
Keyword(s):  
Dynamic Instability ◽  
Time Lapse ◽  
Inducible Promoter ◽  
Spindle Pole ◽  
Yeast Cells ◽  
Microtubule Depolymerization ◽  
Gtp Hydrolysis ◽  
Mutant Proteins ◽  
Gtpase Activation ◽  
Β Tubulin

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.

scholarly journals Bacterial Microtubules Exhibit Polarized Growth, Mixed-Polarity Bundling, and Destabilization by GTP Hydrolysis

2017 ◽  
Author(s):  
César Díaz-Celis ◽  
Viviana I. Risca ◽  
Felipe Hurtado ◽  
Jessica K. Polka ◽  
Scott D. Hansen ◽  
...  
Keyword(s):  
Molecular Motors ◽  
Intracellular Transport ◽  
Complex Dynamics ◽  
Critical Concentration ◽  
Polarized Growth ◽  
Gtp Hydrolysis ◽  
Filament Dynamics ◽  
Mixed Polarity ◽  
Self Association

AbstractBacteria of the genusProsthecobacterexpress homologs of eukaryotic α-and β-tubulin, called BtubA and BtubB, that have been observed to assemble into bacterial microtubules (bMTs). ThebtubABgenes likely entered theProsthecobacterlineage via horizontal gene transfer and may derive from an early ancestor of the modern eukaryotic microtubule (MT). Previous biochemical studies revealed that BtubA/B polymerization is GTP-dependent and reversible and that BtubA/B folding does not require chaperones. To better understand bMT behavior and gain insight into the evolution of microtubule dynamics, we characterizedin vitrobMT assembly using a combination of polymerization kinetics assays, and microscopy. Like eukaryotic microtubules, bMTs exhibit polarized growth with different assembly rates at each end. GTP hydrolysis stimulated by bMT polymerization drives a stochastic mechanism of bMT disassembly that occurs via polymer breakage. We also observed treadmilling (continuous addition and loss of subunits at opposite ends) of bMT fragments. Unlike MTs, polymerization of bMTs requires KCl, which reduces the critical concentration for BtubA/B assembly and induces bMTs to form stable mixed-orientation bundles in the absence of any additional bMT-binding proteins. Our results suggest that at potassium concentrations resembling that inside the cytoplasm ofProsthecobacter, bMT stabilization through self-association may be a default behavior. The complex dynamics we observe in both stabilized and unstabilized bMTs may reflect common properties of an ancestral eukaryotic tubulin polymer.ImportanceMicrotubules are polymers within all eukaryotic cells that perform critical functions: they segregate chromosomes in cell division, organize intracellular transport by serving as tracks for molecular motors, and support the flagella that allow sperm to swim. These functions rely on microtubules remarkable range of tunable dynamic behaviors. Recently discovered bacterial microtubules composed of an evolutionarily related protein are evolved from a missing link in microtubule evolution, the ancestral eukaryotic tubulin polymer. Using microscopy and biochemical approaches to characterize bacterial microtubules, we observed that they exhibit complex and structurally polarized dynamic behavior like eukaryotic microtubules, but differ in how they self-associate into bundles and become destabilized. Our results demonstrate the diversity of mechanisms that microtubule-like filaments employ to promote filament dynamics and monomer turnover.

scholarly journals Epistasis, aneuploidy, and gain-of-function mutations underlie the evolution of resistance to induced microtubule depolymerization

2020 ◽  
Author(s):  
Mattia Pavani ◽  
Paolo Bonaiuti ◽  
Elena Chiroli ◽  
Fridolin Gross ◽  
Federica Natali ◽  
...  
Keyword(s):  
Yeast Cells ◽  
Adaptive Mutation ◽  
Microtubule Depolymerization ◽  
Gain Of Function ◽  
Beta Tubulin ◽  
Microtubule Polymerization ◽  
Evolution Experiment ◽  
Evolution Of Resistance ◽  
Cellular Components ◽  
Chromosome Viii

ABSTRACTMicrotubules, polymers of alpha- and beta-tubulin, are essential cellular components. When microtubule polymerization is hindered, cells are delayed in mitosis, but eventually they manage to proliferate with massive chromosome missegregation. Several studies have analyzed the first cell division upon microtubules impairing conditions. Here, we asked how cells cope on the long term. Taking advantage of mutations in beta-tubulin, we evolved in the lab for ∼150 generations 24 populations of yeast cells unable to properly polymerize microtubules. At the end of the evolution experiment, cells re-gained the ability to form microtubules, and were less sensitive to microtubule depolymerizing drugs. Whole genome sequencing allowed us to identify genes recurrently mutated (tubulins and kinesins) as well as the pervasive duplication of chromosome VIII. We confirmed that mutations found in these genes and disomy of chromosome VIII allow cells to compensate for the original mutation in beta-tubulin. The mutations we identified were mostly gain-of-function, likely re-allowing the proper use of the mutated form of beta-tubulin. When we analyzed the temporal order of mutations leading to resistance in independent populations, we observed multiple times the same series of events: disomy of chromosome VIII followed by one additional adaptive mutation in either tubulins or kinesins. Analyzing the epistatic interactions among different mutations, we observed that some mutations benefited from the disomy of chromosome VIII and others did not. Given that tubulins are highly conserved among eukaryotes, our results are potentially relevant for understanding the emergence of resistance to drugs targeting microtubules, widely used for cancer treatment.

scholarly journals Plasmodium Kinesin-8X associates with mitotic spindles and is essential for oocyst development during parasite proliferation and transmission

2019 ◽  
Author(s):  
Mohammad Zeeshan ◽  
Fiona Shilliday ◽  
Tianyang Liu ◽  
Steven Abel ◽  
Tobias Mourier ◽  
...  
Keyword(s):  
Life Cycle ◽  
Cell Division ◽  
Gene Targeting ◽  
Intracellular Transport ◽  
Regulation Of Gene Expression ◽  
Microtubule Depolymerization ◽  
Expression Of Genes ◽  
Genome Wide ◽  
Spindle Dynamics ◽  
Chromosome Alignment

AbstractKinesin-8 proteins are microtubule motors that are often involved in regulation of mitotic spindle length and chromosome alignment. They move towards the ends of spindle microtubules and regulate the dynamics of these ends due, at least in some species, to their microtubule depolymerization activity. Plasmodium spp. exhibit an atypical endomitotic cell division in which chromosome condensation and spindle dynamics are not well understood in the different proliferative stages. Genome-wide homology analysis of Plasmodium spp. revealed the presence of two Kinesin-8 motor proteins (Kinesin-8X and Kinesin-8B). Here we have studied the biochemical properties of Kinesin-8X and its role in parasite proliferation. In vitro, Kinesin-8X showed motile and depolymerization activities like other Kinesin-8 motors. To understand its role in cell division, we have used protein tagging and live cell imaging to define the location of Plasmodium Kinesin-8X during all proliferative stages of the P berghei life cycle. Furthermore, we have used gene targeting to analyse the function of Kinesin-8X. The results reveal a spatio-temporal involvement of Kinesin-8X in spindle dynamics and its association with both mitotic and meiotic spindles and the putative microtubule organising centre (MTOC). Deletion of the Kinesin-8X gene showed that this protein is required for endomitotic division during oocyst development and is therefore necessary for parasite replication within the mosquito gut, and for transmission to the vertebrate host. Consistently, transcriptome analysis of Δkinesin-8X parasites reveals modulated expression of genes involved mainly in microtubule-based processes, chromosome organisation and the regulation of gene expression supporting a role in cell division.Author SummaryKinesins are microtubule-based motors that play key roles in intracellular transport, cell division and motility. Members of the Kinesin-8 family contribute to chromosome alignment during cell division in many eukaryotes. However, the roles of kinesins in the atypical cell division in Plasmodium, the causative agent of malaria, is not known. In contrast to many other eukaryotes, Plasmodium proliferates by endomitosis, in which genome replication and division occur within a nucleus bounded by a persistent nuclear envelope. We show that the Plasmodium genome encodes only nine kinesins and we further investigate the role of Kinesin-8X throughout the Plasmodium life cycle using biochemical and gene targeting approaches. We show that Plasmodium Kinesin-8X has microtubule-based motility and depolymerization activity. We also show that Kinesin-8X is probably localized on putative MTOCs and spindles during cell division in most of the stages of P. berghei life cycle. By gene deletion we demonstrate that Kinesin-8X is essential for normal oocyst development and sporozoite formation. Genome-wide RNA analysis of Δkinesin-8X parasites reveals modulated expression of genes involved in microtubule-based processes. Overall, the data suggest that Kinesin-8X is a molecular motor that plays essential roles during endomitosis in oocyst development in the mosquito, contributing to parasite transmission.

scholarly journals The Saccharomyces cerevisiae Kinesin-related Motor Kar3p Acts at Preanaphase Spindle Poles to Limit the Number and Length of Cytoplasmic Microtubules

1997 ◽  
Vol 137 (2) ◽  
pp. 417-431 ◽  
Author(s):  
William Saunders ◽  
David Hornack ◽  
Valerie Lengyel ◽  
Changchun Deng
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Spindle Pole Body ◽  
Spindle Pole ◽  
Body Region ◽  
Microtubule Depolymerization ◽  
Growth Defects ◽  
Microtubule Polymerization ◽  
Late Anaphase ◽  
A Cell ◽  
Cytoplasmic Microtubules

The Saccharomyces cerevisiae kinesin-related motor Kar3p, though known to be required for karyogamy, plays a poorly defined, nonessential role during vegetative growth. We have found evidence suggesting that Kar3p functions to limit the number and length of cytoplasmic microtubules in a cell cycle–specific manner. Deletion of KAR3 leads to a dramatic increase in cytoplasmic microtubules, a phenotype which is most pronounced from START through the onset of anaphase but less so during late anaphase in synchronized cultures. We have immunolocalized HA-tagged Kar3p to the spindle pole body region, and fittingly, Kar3p was not detected by late anaphase. A microtubule depolymerizing activity may be the major vegetative role for Kar3p. Addition of the microtubule polymerization inhibitors nocodazol or benomyl to the medium or deletion of the nonessential α-tubulin TUB3 gene can mostly correct the abnormal microtubule arrays and other growth defects of kar3 mutants, suggesting that these phenotypes result from excessive microtubule polymerization. Microtubule depolymerization may also be the mechanism by which Kar3p acts in opposition to the anaphase B motors Cin8p and Kip1p. A preanaphase spindle collapse phenotype of cin8 kip1 mutants, previously shown to involve Kar3p, is markedly delayed when microtubule depolymerization is inhibited by the tub2-150 mutation. These results suggest that the Kar3p motor may act to regulate the length and number of microtubules in the preanaphase spindle.

Abstract 13912: 17-Beta-Estradiol Directly Regulates Microtubule Dynamics: New Insights Into Sex-Differences in Right Ventricular Function in Pulmonary Hypertension

Circulation ◽  
2020 ◽  
Vol 142 (Suppl_3) ◽  
Author(s):  
Sasha Z Prisco ◽  
Ping Y Xiong ◽  
Rebecca Goldblum ◽  
Francois Potus ◽  
Kenneth Martinez Algarin ◽  
...  
Keyword(s):  
Pulmonary Hypertension ◽  
Sex Differences ◽  
Right Ventricular ◽  
Molecular Mechanisms ◽  
Microtubule Dynamics ◽  
Microtubule Depolymerization ◽  
Tirf Microscopy ◽  
Female Sex ◽  
Microtubule Polymerization ◽  
Rv Function

Introduction: Female sex is associated with better right ventricular (RV) function in pulmonary hypertension (PH). The female sex hormone 17-beta-estradiol is postulated to mediate these differences, but the molecular mechanisms underlying these observations are incompletely defined. Interestingly, 17-beta-estradiol induces microtubule depolymerization in cell culture, which may be relevant to RV dysfunction because microtubule remodeling promotes RV dysfunction via dysregulation of junctophilin-2 (MT-JPH2 pathway). We speculate that 17-beta-estradiol modulates the MT-JPH2 pathway and preserves RV function in PH. Methods: Pressure-volume assessments quantified RV function in monocrotaline (MCT) and pulmonary artery-banded (PAB) rats. Immunoblots quantified the tubulin and junctophilin-2 protein content in RV extracts. Echocardiography quantified RV function by RV fractional area change for 379 human PH patients. Sedimentation experiments, fluorescence-based polymerization assessments, and total internal reflection fluorescence (TIRF) microscopy examined the effects of 17-beta-estradiol on microtubules. Results: Female sex results in better RV function and less dysregulation of the MT-JPH2 pathway in both MCT and PAB rats. Moreover, in human PH, female sex was associated with better RV function, which persisted after adjusting for afterload. 17-beta-estradiol inhibited microtubule polymerization in vitro and TIRF microscopy showed 17-beta-estradiol localized to microtubule tips and prevented further microtubule polymerization. Conclusions: Preclinical and human studies show that females are better able to tolerate RV pressure overload. There are blunted microtubule-mediated t-tubule remodeling and preserved RV function in female MCT and PAB rats. In human PH, females have better RV function. These findings may be due to 17-beta-estradiol directly regulating microtubule dynamics as shown by sedimentation and polymerization assays and TIRF microscopy. These results provide additional insights into sex-differences in RV function in PH.

Crystallographic studies of elongation factor G

1995 ◽  
Vol 73 (11-12) ◽  
pp. 1209-1216 ◽  
Author(s):  
Anders Liljas ◽  
Arnthor Ævarsson ◽  
Salam Al-Karadaghi ◽  
Maria Garber ◽  
Julia Zheltonosova ◽  
...  
Keyword(s):  
Crystal Structures ◽  
Conformational Change ◽  
Conformational Changes ◽  
Elongation Factor ◽  
Elongation Factors ◽  
Elongation Factor G ◽  
Conformational States ◽  
Gtp Hydrolysis ◽  
Large Conformational Change ◽  
Factor G

The elongation factors G (EF-G) and Tu (EF-Tu) go through a number of conformation states in their functional cycles. Since they both are GTPases, have similar G domains and domains II, and have similar interactions with the nucleotides, then GTP hydrolysis must occur in similar ways. The crystal structures of two conformational states are known for EF-G and three are known for EF-Tu. The conformations of EF-G∙GDP and EF-Tu∙GTP are closely related. EF-Tu goes through a large conformational change upon GTP cleavage. This conformational change is to a large extent due to an altered interaction between the G domain and domains II and III. A number of kirromycin-resistant mutations are situated at the interface between domains I and III. The interface between the G domain and domain V in EF-G corresponds with this dynamic interface in EF-Tu. The contact area in EF-G is small and dominated by interactions between charged amino acids, which are part of a system that is observed to undergo conformational changes. Furthermore, a number of fusidic acid resistant mutants have been identified in this area. All of this evidence makes it likely that EF-G undergoes a large conformational change in its functional cycle. If the structures and conformational states of the elongation factors are related to a scheme in which the ribosome oscillates between two conformations, the pretranslocational and posttranslocational states, a model is arrived at in which EF-Tu drives the reaction in one direction and EF-G in the opposite. This may lead to the consequence that the GTP state of one factor is similar to the GDP state of the other. At the GTP hydrolysis state, the structures of the factors will be close to superimposable.Key words: elongation factor G, elongation factor Tu, crystal structures, conformational changes, ribosomal conformation.

Time-resolved X-ray crystallographic study of the conformational change in Ha-Ras p21 protein on GTP hydrolysis

Nature ◽  
1990 ◽  
Vol 345 (6273) ◽  
pp. 309-315 ◽  
Author(s):  
Ilme Schlichting ◽  
Steven C. Almo ◽  
Gert Rapp ◽  
Keith Wilson ◽  
Kyriakos Petratos ◽  
...  
Keyword(s):  
Conformational Change ◽  
Gtp Hydrolysis ◽  
Time Resolved ◽  
P21 Protein ◽  
X Ray ◽  
Crystallographic Study ◽  
Ras P21

scholarly journals The Rab8 GTPase selectively regulates AP-1B–dependent basolateral transport in polarized Madin-Darby canine kidney cells

2003 ◽  
Vol 163 (2) ◽  
pp. 339-350 ◽  
Author(s):  
Agnes Lee Ang ◽  
Heike Fölsch ◽  
Ulla-Maija Koivisto ◽  
Marc Pypaert ◽  
Ira Mellman
Keyword(s):  
Membrane Proteins ◽  
Intracellular Transport ◽  
Rho Gtpase ◽  
Dominant Negative ◽  
Recycling Endosome ◽  
Gtp Hydrolysis ◽  
Clathrin Adaptor ◽  
Dominant Negative Allele ◽  
Dependent Transport ◽  
Darby Canine Kidney

The AP-1B clathrin adaptor complex plays a key role in the recognition and intracellular transport of many membrane proteins destined for the basolateral surface of epithelial cells. However, little is known about other components that act in conjunction with AP-1B. We found that the Rab8 GTPase is one such component. Expression of a constitutively activated GTP hydrolysis mutant selectively inhibited basolateral (but not apical) transport of newly synthesized membrane proteins. Moreover, the effects were limited to AP-1B–dependent basolateral cargo; basolateral transport of proteins containing dileucine targeting motifs that do not interact with AP-1B were targeted normally despite overexpression of mutant Rab8. Similar results were obtained for a dominant-negative allele of the Rho GTPase Cdc42, previously implicated in basolateral transport but now shown to be selective for the AP-1B pathway. Rab8-GFP was localized to membranes in the TGN-recycling endosome, together with AP-1B complexes and the closely related but ubiquitously expressed AP-1A complex. However, expression of active Rab8 caused a selective dissociation of AP-1B complexes, reflecting the specificity of Rab8 for AP-1B–dependent transport.

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