scholarly journals EB3-informed dynamics of the microtubule stabilizing cap during stalled growth

2021 ◽  
Author(s):  
Maurits Kok ◽  
Florian Huber ◽  
Svenja-Marei Kalisch ◽  
Marileen Dogterom
Keyword(s):  
Growth Velocity ◽  
Hydrolysis Rate ◽  
Exact Relation ◽  
Gtp Hydrolysis ◽  
Lifetime Distributions ◽  
Microtubule Stability ◽  
In Vitro Reconstitution ◽  
1D Model ◽  
Microtubule Growth

Microtubule stability is known to be governed by a stabilizing GTP/GDP-Pi cap, but the exact relation between growth velocity, GTP hydrolysis and catastrophes remains unclear. We investigate the dynamics of the stabilizing cap through in vitro reconstitution of microtubule dynamics in contact with micro-fabricated barriers, using the plus-end binding protein GFP-EB3 as a marker for the nucleotide state of the tip. The interaction of growing microtubules with steric objects is known to slow down microtubule growth and accelerate catastrophes. We show that the lifetime distributions of stalled microtubules, as well as the corresponding lifetime distributions of freely growing microtubules, can be fully described with a simple phenomenological 1D model based on noisy microtubule growth and a single EB3-dependent hydrolysis rate. This same model is furthermore capable of explaining both the previously reported mild catastrophe dependence on microtubule growth rates and the catastrophe statistics during tubulin washout experiments.

scholarly journals Dilution of individual microtubules observed in real time in vitro: evidence that cap size is small and independent of elongation rate.

1991 ◽  
Vol 114 (1) ◽  
pp. 73-81 ◽  
Author(s):  
R A Walker ◽  
N K Pryer ◽  
E D Salmon
Keyword(s):  
Dynamic Instability ◽  
Elongation Rate ◽  
Gtp Hydrolysis ◽  
Microtubule Stability ◽  
Assembly Mechanism ◽  
High Elongation ◽  
Microtubule Growth ◽  
Hydrolysis Of ◽  
Brain Tubulin

Although the mechanism of microtubule dynamic instability is thought to involve the hydrolysis of tubulin-bound GTP, the mechanism of GTP hydrolysis and the basis of microtubule stability are controversial. Video microscopy of individual microtubules and dilution protocols were used to examine the size and lifetime of the stabilizing cap. Purified porcine brain tubulin (7-23 microM) was assembled at 37 degrees C onto both ends of isolated sea urchin axoneme fragments in a miniature flow cell to give a 10-fold variation in elongation rate. The tubulin concentration in the region of microtubule growth could be diluted rapidly (by 84% within 3 s of the onset of dilution). Upon perfusion with buffer containing no tubulin, microtubules experienced a catastrophe (conversion from elongation to rapid shortening) within 4-6 s on average after dilution to 16% of the initial concentration, independent of the predilution rate of elongation and length. Based on extrapolation of catastrophe frequency to zero tubulin concentration, the estimated lifetime of the stable cap after infinite dilution was less than 3-4 s for plus and minus ends, much shorter than the approximately 200 s observed at steady state (Walker, R. A., E. T. O'Brien, N. K. Pryer, M. Soboeiro, W. A. Voter, H. P. Erickson, and E. D. Salmon. 1988. J. Cell Biol. 107:1437-1448.). We conclude that during elongation, both plus and minus ends are stabilized by a short region (approximately 200 dimers or less) and that the size of the stable cap is independent of 10-fold variation in elongation rate. These results eliminate models of dynamic instability which predict extensive "build-up" stabilizing caps and support models which constrain the cap to the elongating tip. We propose that the cell may take advantage of such an assembly mechanism by using "catastrophe factors" that can promote frequent catastrophe even at high elongation rates by transiently binding to microtubule ends and briefly inhibiting GTP-tubulin association.

scholarly journals XMAP215 promotes microtubule catastrophe by disrupting the growing microtubule end

2020 ◽  
Author(s):  
Veronica Farmer ◽  
Göker Arpağ ◽  
Sarah Hall ◽  
Marija Zanic
Keyword(s):  
Growth Rate ◽  
Growth Rates ◽  
Fast Growth ◽  
Fast Growing ◽  
Microtubule Stability ◽  
Large Fluctuations ◽  
Microtubule Growth ◽  
Enhanced Stability

ABSTRACTThe GTP-tubulin cap is widely accepted to protect microtubules against catastrophe. The GTP-cap size is thought to increase with the microtubule growth rate, presumably endowing fast-growing microtubules with enhanced stability. It is unknown what GTP-cap properties permit frequent microtubule catastrophe despite fast growth. Here, we investigate microtubules grown in vitro in the presence and absence of the microtubule polymerase XMAP215. Using EB1 as a GTP-cap marker, we find that GTP-cap size increases regardless of whether growth acceleration is achieved by increasing tubulin concentration or by XMAP215. In spite of the increased mean GTP-cap size, microtubules grown with XMAP215 display increased catastrophe frequency, in contrast to microtubules grown with more tubulin, for which catastrophe is abolished. However, microtubules polymerized with XMAP215 have large fluctuations in growth rate and EB1 intensity; display tapered and curled ends; and undergo catastrophe at faster growth rates and with higher EB1 end-localization. Our results underscore the role of growth irregularities in overall microtubule stability.

scholarly journals On the Relationship Between EB-3 Profiles and Microtubules Growth in Cultured Cells

2021 ◽  
Vol 8 ◽  
Author(s):  
Arshat Urazbaev ◽  
Anara Serikbaeva ◽  
Anna Tvorogova ◽  
Azamat Dusenbayev ◽  
Sholpan Kauanova ◽  
...  
Keyword(s):  
Growth Velocity ◽  
Cultured Cells ◽  
Time Lapse ◽  
Living Cells ◽  
Time Intervals ◽  
Mean Values ◽  
Microtubule Growth ◽  
Dynamic Structures

Microtubules are dynamic structures undergoing rapid growth and shrinkage in living cells and in vitro. The growth of microtubules in vitro was analyzed with subpixel precision (Maurer et al., Current Biology, 2014, 24 (4), 372–384); however, to what extent these results could be applied for microtubules growing in vivo remains largely unknown. Particularly, the question is whether microtubule growth velocity in cells could be sufficiently approximated by a Gaussian distribution or its variability requires a more sophisticated description? Addressing this question, we used time-lapse microscopy and mathematical modeling, and we analyzed EB-3 comets forming on microtubules of cultured cells with subpixel precision. Parameters of comets (shape, form, and velocity) were used as topological characteristics of 3D voxel objects. Using regression analysis, we determined the real positions of the microtubule tips in time-lapse sequences. By exponential decay fitting of the restored comet intensity profile, we found that in vivo EB-3 rapidly exchanges on growing microtubule ends with a decoration time ∼ 2 s. We next developed the model showing that the best correlation between comet length and microtubule end growth velocity is at time intervals close to the decoration time. In the cells, EB comet length positively correlates with microtubule growth velocity in preceding time intervals, while demonstrating no correlation in subsequent time intervals. Correlation between comet length and instantaneous growth velocity of microtubules remains under nocodazole treatment when mean values of both parameters decrease. Our data show that the growth of microtubules in living cells is well-approximated by a constant velocity with large stochastic fluctuations.

scholarly journals Inhibition of GTP hydrolysis by Sar1p causes accumulation of vesicles that are a functional intermediate of the ER-to-Golgi transport in yeast

1994 ◽  
Vol 124 (4) ◽  
pp. 425-434 ◽  
Author(s):  
T Oka ◽  
A Nakano
Keyword(s):  
Protein Transport ◽  
Active Form ◽  
Integral Membrane Protein ◽  
Temperature Sensitive ◽  
Vesicle Formation ◽  
Gtp Hydrolysis ◽  
Golgi Transport ◽  
Transport Vesicles ◽  
In Vitro Reconstitution

The SAR1 gene product (Sar1p), a 21-kD GTPase, is a key component of the ER-to-Golgi transport in the budding yeast. We previously reported that the in vitro reconstitution of protein transport from the ER to the Golgi was dependent on Sar1p and Sec12p (Oka, T., S. Nishikawa, and A. Nakano. 1991. J. Cell Biol. 114:671-679). Sec12p is an integral membrane protein in the ER and is essential for the Sar1 function. In this paper, we show that Sar1p can remedy the temperature-sensitive defect of the sec12 mutant membranes, which is in the formation of ER-to-Golgi transport vesicles. The addition of Sar1p promotes vesicle formation from the ER irrespective of the GTP- or GTP gamma S-bound form, indicating that the active form of Sar1p but not the hydrolysis of GTP is required for this process. The inhibition of GTP hydrolysis blocks transport of vesicles to the Golgi and thus causes their accumulation. The accumulating vesicles, which carry Sar1p on them, can be separated from other membranes, and, after an appropriate wash that removes Sar1p, are capable of delivering the content to the Golgi when added back to fresh membranes. Thus we have established a new method for isolation of functional intermediate vesicles in the ER-to-Golgi transport. The sec23 mutant is defective in activation of Sar1 GTPase (Yoshihisa, T., C. Barlowe, and R. Schekman. 1993. Science (Wash. DC). 259:1466-1468). The membranes and cytosol from the sec23 mutant show only a partial defect in vesicle formation and this defect is also suppressed by the increase of Sar1p. Again GTP hydrolysis is not needed for the suppression of the defect in vesicle formation. Based on these results, we propose a model in which Sar1p in the GTP-bound form is required for the formation of transport vesicles from the ER and the GTP hydrolysis by Sar1p is essential for entering the next step of vesicular transport to the Golgi apparatus.

scholarly journals The speed of GTP hydrolysis determines GTP cap size and controls microtubule stability

2019 ◽  
Author(s):  
Johanna Roostalu ◽  
Claire Thomas ◽  
Nicholas I. Cade ◽  
Simone Kunzelmann ◽  
Ian A. Taylor ◽  
...  
Keyword(s):  
Single Molecule ◽  
Critical Importance ◽  
Gtp Hydrolysis ◽  
Diverse Range ◽  
Slowing Down ◽  
High Affinity ◽  
Microtubule Stability ◽  
Kinetics Of ◽  
Microtubule Function

ABSTRACTMicrotubules are bistable cytoskeletal polymers whose function depends on their property to switch between states of growth and shrinkage 1. Growing microtubules are thought to be stabilized by a GTP cap at their ends 2-5. The nature of this cap, however, is still poorly understood. How GTP hydrolysis determines the properties of the GTP cap and hence microtubule stability is unclear. End Binding proteins (EBs) recruit a diverse range of regulators of microtubule function to growing microtubule ends 6. Whether these regulatory platforms at growing microtubule ends are identical to the GTP cap is not known. Using mutated human tubulin with blocked GTP hydrolysis, we demonstrate in microscopy-based in vitro reconstitutions that EB proteins bind with high affinity to the GTP conformation of microtubules. Slowing-down GTP hydrolysis leads to extended GTP caps and consequently hyper-stable microtubules. Single molecule experiments reveal that the microtubule conformation gradually changes in the cap as GTP is hydrolyzed. These results demonstrate the critical importance of the kinetics of GTP hydrolysis for microtubule stability; and establish that the GTP cap coincides with the EB-binding regulatory hub that modulates microtubule cytoskeleton function in cells.

scholarly journals Cross-linkers at growing microtubule ends generate forces that drive actin transport

2021 ◽  
Author(s):  
Celine Alkemade ◽  
Harmen Wierenga ◽  
Vladimir A. Volkov ◽  
Magdalena Preciado-López ◽  
Anna Akhmanova ◽  
...  
Keyword(s):  
Friction Force ◽  
Actin Filaments ◽  
Active Networks ◽  
Filament Length ◽  
Transport Time ◽  
Cellular Processes ◽  
In Vitro Reconstitution ◽  
Microtubule Growth ◽  
Actin Remodelling

The actin and microtubule cytoskeletons form active networks in the cell that can contract and remodel, resulting in vital cellular processes as cell division and motility. Motor proteins play an important role in generating the forces required for these processes, but more recently the concept of passive cross-linkers being able to generate forces has emerged. So far, these passive cross-linkers have been studied in the context of separate actin and microtubule systems. Here, we show that cross-linkers also allow actin and microtubules to exert forces on each other. More specifically, we study single actin filaments that are cross-linked to growing microtubule ends, using in vitro reconstitution, computer simulations, and a minimal theoretical model. We show that microtubules can transport actin filaments over large (micrometer-range) distances, and find that this transport results from two antagonistic forces arising from the binding of cross-linkers to the overlap between the actin and microtubule filaments. The cross-linkers attempt to maximize the overlap between the actin and the tip of the growing microtubules, creating an affinity-driven forward condensation force, and simultaneously create a competing friction force along the microtubule lattice. We predict and verify experimentally how the average transport time depends on the actin filament length and the microtubule growth velocity, confirming the competition between a forward condensation force and a backward friction force. In addition, we theoretically predict and experimentally verify that the condensation force is of the order of 0.1pN. Thus, our results reveal a new mechanism for local actin remodelling by growing microtubules.

How motor proteins influence microtubule polymerization dynamics

2000 ◽  
Vol 113 (24) ◽  
pp. 4379-4389 ◽  
Author(s):  
A.W. Hunter ◽  
L. Wordeman
Keyword(s):  
Intracellular Transport ◽  
Motor Proteins ◽  
Force Production ◽  
Nucleotide Hydrolysis ◽  
Microtubule Polymerization ◽  
Microtubule Stability ◽  
Microtubule Growth ◽  
Chromosome Movements ◽  
Shed Light

The interplay between microtubules and microtubule-based motors is fundamental to basic aspects of cellular function, such as the intracellular transport of organelles and alterations in cellular morphology during cell locomotion and division. Motor proteins are unique in that they couple nucleotide hydrolysis to force production that can do work. The force transduction by proteins belonging to the kinesin and dynein superfamilies has been thought only to power movement of these motors along the surface of microtubules; however, a growing body of evidence, both genetic and biochemical, suggests that motors can also directly influence the polymerization dynamics of microtubules. For example, at the vertebrate kinetochore, motors interact directly with microtubule ends and modulate polymerization dynamics to orchestrate chromosome movements during mitosis. Although a role for motors in regulating microtubule length has been established, the mechanisms used by motors to promote microtubule growth or shrinkage are unclear, as is an understanding of why cells might choose motors to control dynamics rather than a variety of non-motor proteins known to affect microtubule stability. Elucidation of the exact mechanisms by which motors alter the exchange of tubulin subunits at microtubule ends in vitro may shed light on how microtubule stability is regulated to produce the array of dynamic behavior seen in cells.

scholarly journals Actin filaments regulate microtubule growth at the centrosome

2018 ◽  
Author(s):  
Daisuke Inoue ◽  
Dorian Obino ◽  
Francesca Farina ◽  
Jérémie Gaillard ◽  
Christophe Guerin ◽  
...  
Keyword(s):  
Cell Adhesion ◽  
Steric Hindrance ◽  
Actin Filaments ◽  
Network Architecture ◽  
Lymphocyte Activation ◽  
Local Network ◽  
Actin Network ◽  
In Vitro Reconstitution ◽  
Microtubule Growth

AbstractThe centrosome is the main microtubule-organizing centre. It also organizes a local network of actin filaments. However, the precise function of the actin network at the centrosome is not well understood. Here we show that increasing densities of actin filaments at the centrosome of lymphocytes were correlated with reduced amounts of microtubules. Furthermore, lymphocyte activation resulted in centrosomal-actin disassembly and an increase in microtubule number. To further investigate the direct crosstalk between actin and microtubules at the centrosome, we performed in vitro reconstitution assays based on (i) purified centrosomes and (ii) on the co-micropatterning of microtubule seeds and actin filaments. The two assays demonstrated that actin filaments perturb microtubule growth by steric hindrance. Finally, we showed that cell adhesion and spreading leads to lower densities of centrosomal actin thus resulting in higher microtubule growth. Hence we propose a novel mechanism by which the number of centrosomal microtubules is regulated by cell adhesion and actin-network architecture.

scholarly journals In vitro reconstitution reveals phosphoinositides as cargo-release factors and activators of the ARF6 GAP ADAP1

2020 ◽  
Vol 118 (1) ◽  
pp. e2010054118
Author(s):  
Christian Duellberg ◽  
Albert Auer ◽  
Nikola Canigova ◽  
Katrin Loibl ◽  
Martin Loose
Keyword(s):  
Molecular Motors ◽  
Small Gtpase ◽  
Complex Dynamic ◽  
Gtp Hydrolysis ◽  
Dendrite Branching ◽  
Precise Control ◽  
In Vitro Reconstitution ◽  
Adp Ribosylation Factor ◽  
Dynamic Interplay

The differentiation of cells depends on a precise control of their internal organization, which is the result of a complex dynamic interplay between the cytoskeleton, molecular motors, signaling molecules, and membranes. For example, in the developing neuron, the protein ADAP1 (ADP-ribosylation factor GTPase-activating protein [ArfGAP] with dual pleckstrin homology [PH] domains 1) has been suggested to control dendrite branching by regulating the small GTPase ARF6. Together with the motor protein KIF13B, ADAP1 is also thought to mediate delivery of the second messenger phosphatidylinositol (3,4,5)-trisphosphate (PIP3) to the axon tip, thus contributing to PIP3polarity. However, what defines the function of ADAP1 and how its different roles are coordinated are still not clear. Here, we studied ADAP1’s functions using in vitro reconstitutions. We found that KIF13B transports ADAP1 along microtubules, but that PIP3as well as PI(3,4)P2act as stop signals for this transport instead of being transported. We also demonstrate that these phosphoinositides activate ADAP1’s enzymatic activity to catalyze GTP hydrolysis by ARF6. Together, our results support a model for the cellular function of ADAP1, where KIF13B transports ADAP1 until it encounters high PIP3/PI(3,4)P2concentrations in the plasma membrane. Here, ADAP1 disassociates from the motor to inactivate ARF6, promoting dendrite branching.

scholarly journals The human tRNA taurine modification enzyme GTPBP3 is an active GTPase linked to mitochondrial diseases

2021 ◽  
Author(s):  
Gui-Xin Peng ◽  
Yong Zhang ◽  
Qin-Qin Wang ◽  
Qing-Run Li ◽  
Hong Xu ◽  
...  
Keyword(s):  
Mitochondrial Diseases ◽  
Mechanistic Study ◽  
Gtp Hydrolysis ◽  
Wobble Position ◽  
In Vitro Reconstitution ◽  
Solid Foundation ◽  
Mature Enzyme ◽  
First Time

Abstract GTPBP3 and MTO1 cooperatively catalyze 5-taurinomethyluridine (τm5U) biosynthesis at the 34th wobble position of mitochondrial tRNAs. Mutations in tRNAs, GTPBP3 or MTO1, causing τm5U hypomodification, lead to various diseases. However, efficient in vitro reconstitution and mechanistic study of τm5U modification have been challenging, in part due to the lack of pure and active enzymes. A previous study reported that purified human GTPBP3 (hGTPBP3) is inactive in GTP hydrolysis. Here, we identified the mature form of hGTPBP3 and showed that hGTPBP3 is an active GTPase in vitro that is critical for tRNA modification in vivo. Unexpectedly, the isolated G domain and a mutant with the N-terminal domain truncated catalyzed GTP hydrolysis to only a limited extent, exhibiting high Km values compared with that of the mature enzyme. We further described several important pathogenic mutations of hGTPBP3, associated with alterations in hGTPBP3 localization, structure and/or function in vitro and in vivo. Moreover, we discovered a novel cytoplasm-localized isoform of hGTPBP3, indicating an unknown potential noncanonical function of hGTPBP3. Together, our findings established, for the first time, the GTP hydrolysis mechanism of hGTPBP3 and laid a solid foundation for clarifying the τm5U modification mechanism and etiology of τm5U deficiency-related diseases.

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