New understanding of the effects of microtubule-associated proteins on dynamic instability, including the role of tau in neuronal function and disease

2021 ◽  
Author(s):  
Timothy Ottum Austin
Keyword(s):  
Dynamic Instability ◽  
Neuronal Function ◽  
Microtubule Associated Proteins ◽  
Associated Proteins

Analysis of the Mechanism of Microtubule Dynamic Instability Using a UV Microbeam to Sever Elongating Microtubules

1988 ◽  
Vol 46 ◽  
pp. 122-123
Author(s):  
R.A Walker ◽  
S. Inoue ◽  
E.D. Salmon
Keyword(s):  
Dynamic Instability ◽  
Microtubule Dynamic ◽  
Gtp Hydrolysis ◽  
Abrupt Transition ◽  
Microtubule Associated Proteins ◽  
Asymmetrical Structure ◽  
Associated Proteins

Microtubules polymerized in vitro from tubulin purified free of microtubule-associated proteins exhibit dynamic instability (1,2,3). Free microtubule ends exist in persistent phases of elongation or rapid shortening with infrequent, but, abrupt transitions between these phases. The abrupt transition from elongation to rapid shortening is termed catastrophe and the abrupt transition from rapid shortening to elongation is termed rescue. A microtubule is an asymmetrical structure. The plus end grows faster than the minus end. The frequency of catastrophe of the plus end is somewhat greater than the minus end, while the frequency of rescue of the plus end in much lower than for the minus end (4).The mechanism of catastrophe is controversial, but for both the plus and minus microtubule ends, catastrophe is thought to be dependent on GTP hydrolysis. Microtubule elongation occurs by the association of tubulin-GTP subunits to the growing end. Sometime after incorporation into an elongating microtubule end, the GTP is hydrolyzed to GDP, yielding a core of tubulin-GDP capped by tubulin-GTP (“GTP-cap”).

Modulation of microtubule dynamic instability in vivo by brain microtubule associated proteins

1995 ◽  
Vol 108 (4) ◽  
pp. 1679-1689 ◽  
Author(s):  
R. Dhamodharan ◽  
P. Wadsworth
Keyword(s):  
Dynamic Behavior ◽  
Dynamic Instability ◽  
Average Rate ◽  
Stable Maps ◽  
Microtubule Dynamic ◽  
Unit Distance ◽  
Microtubule Associated Proteins ◽  
Heat Stable ◽  
Associated Proteins

Heat-stable brain microtubule associated proteins (MAPs) and purified microtubule associated protein 2 (MAP-2) were microinjected into cultured BSC-1 cells which had been previously injected with rhodamine-labeled tubulin. The dynamic instability behavior of individual microtubules was then examined using low-light-level fluorescence microscopy and quantitative microtubule tracking methods. Both MAP preparations suppressed microtubule dynamics in vivo, by reducing the average rate and extent of both growing and shortening events. The average duration of growing events was not affected. When measured as events/unit time, heat-stable MAPs and MAP-2 did not significantly alter the frequency of rescue; the frequency of catastrophe was decreased approximately two-fold by heat-stable MAPs and MAP-2. When transition frequencies were calculated as events/unit distance, both MAP preparations increased the frequency of rescue, without altering the frequency of catastrophe. The percentage of total time spent in the phases of growth, shrink and pause was determined. Both MAP-2 and heat-stable MAPs decreased the percentage of time spent shortening, increased the percentage of time spent paused, and had no effect on percentage of time spent growing. Heat-stable MAPs increased the average pause duration, decreased the average number of events per minute per microtubule and increased the probability that a paused microtubule would switch to growing rather than shortening. The results demonstrate that addition of MAPs to living cells reduces the dynamic behavior of individual microtubules primarily by suppressing the magnitude of dynamic events and increasing the time spent in pause, where no change in the microtubule length can be detected. The results further suggest that the expression of MAPs directly contributes to cell type-specific microtubule dynamic behavior.

scholarly journals The structured core of human β tubulin confers isotype-specific polymerization properties

2016 ◽  
Vol 213 (4) ◽  
pp. 425-433 ◽  
Author(s):  
Melissa C. Pamula ◽  
Shih-Chieh Ti ◽  
Tarun M. Kapoor
Keyword(s):  
Dynamic Instability ◽  
Sequence Divergence ◽  
Regulatory Proteins ◽  
Microtubule Dynamic ◽  
Microtubule Associated Proteins ◽  
Cytoskeleton Organization ◽  
Wide Range ◽  
Associated Proteins ◽  
And Function ◽  
Β Tubulin

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

scholarly journals The microtubule lattice and plus-end association of Drosophila Mini spindles is spatially regulated to fine-tune microtubule dynamics

2011 ◽  
Vol 22 (22) ◽  
pp. 4343-4361 ◽  
Author(s):  
Joshua D. Currie ◽  
Shannon Stewman ◽  
Gregory Schimizzi ◽  
Kevin C. Slep ◽  
Ao Ma ◽  
...  
Keyword(s):  
Dynamic Instability ◽  
Function Analysis ◽  
Microtubule Dynamics ◽  
Cell Periphery ◽  
Cell Interior ◽  
Microtubule Associated Proteins ◽  
Contact Sites ◽  
Associated Proteins ◽  
Fine Tune

Individual microtubules (MTs) exhibit dynamic instability, a behavior in which they cycle between phases of growth and shrinkage while the total amount of MT polymer remains constant. Dynamic instability is promoted by the conserved XMAP215/Dis1 family of microtubule-associated proteins (MAPs). In this study, we conducted an in vivo structure–function analysis of the Drosophila homologue Mini spindles (Msps). Msps exhibits EB1-dependent and spatially regulated MT localization, targeting to microtubule plus ends in the cell interior and decorating the lattice of growing and shrinking microtubules in the cell periphery. RNA interference rescue experiments revealed that the NH2-terminal four TOG domains of Msps function as paired units and were sufficient to promote microtubule dynamics and EB1 comet formation. We also identified TOG5 and novel inter-TOG linker motifs that are required for targeting Msps to the microtubule lattice. These novel microtubule contact sites are necessary for the interplay between the conserved TOG domains and inter-TOG MT binding that underlies the ability of Msps to promote MT dynamic instability.

scholarly journals Dynamic instability of individual microtubules analyzed by video light microscopy: rate constants and transition frequencies.

1988 ◽  
Vol 107 (4) ◽  
pp. 1437-1448 ◽  
Author(s):  
R A Walker ◽  
E T O'Brien ◽  
N K Pryer ◽  
M F Soboeiro ◽  
W A Voter ◽  
...  
Keyword(s):  
Rate Constants ◽  
Dynamic Instability ◽  
Dissociation Rate ◽  
Microtubule Associated Proteins ◽  
First Order ◽  
Associated Proteins ◽  
Dissociation Rate Constants ◽  
Elongation Phase ◽  
Association Rate Constants ◽  
Brain Tubulin

We have developed video microscopy methods to visualize the assembly and disassembly of individual microtubules at 33-ms intervals. Porcine brain tubulin, free of microtubule-associated proteins, was assembled onto axoneme fragments at 37 degrees C, and the dynamic behavior of the plus and minus ends of microtubules was analyzed for tubulin concentrations between 7 and 15.5 microM. Elongation and rapid shortening were distinctly different phases. At each end, the elongation phase was characterized by a second order association and a substantial first order dissociation reaction. Association rate constants were 8.9 and 4.3 microM-1 s-1 for the plus and minus ends, respectively; and the corresponding dissociation rate constants were 44 and 23 s-1. For both ends, the rate of tubulin dissociation equaled the rate of tubulin association at 5 microM. The rate of rapid shortening was similar at the two ends (plus = 733 s-1; minus = 915 s-1), and did not vary with tubulin concentration. Transitions between phases were abrupt and stochastic. As the tubulin concentration was increased, catastrophe frequency decreased at both ends, and rescue frequency increased dramatically at the minus end. This resulted in fewer rapid shortening phases at higher tubulin concentrations for both ends and shorter rapid shortening phases at the minus end. At each concentration, the frequency of catastrophe was slightly greater at the plus end, and the frequency of rescue was greater at the minus end. Our data demonstrate that microtubules assembled from pure tubulin undergo dynamic instability over a twofold range of tubulin concentrations, and that the dynamic instability of the plus and minus ends of microtubules can be significantly different. Our analysis indicates that this difference could produce treadmilling, and establishes general limits on the effectiveness of length redistribution as a measure of dynamic instability. Our results are consistent with the existence of a GTP cap during elongation, but are not consistent with existing GTP cap models.

scholarly journals Generation of microtubule stability subclasses by microtubule-associated proteins: implications for the microtubule "dynamic instability" model.

1985 ◽  
Vol 101 (5) ◽  
pp. 1680-1689 ◽  
Author(s):  
D Job ◽  
M Pabion ◽  
R L Margolis
Keyword(s):  
Dynamic Instability ◽  
Protein Activity ◽  
Microtubule Dynamic ◽  
Microtubule Associated Proteins ◽  
Microtubule Stability ◽  
Low Concentrations ◽  
Protein Map ◽  
Associated Proteins ◽  
Specific Influence ◽  
Assay Conditions

We have developed a method to distinguish microtubule associated protein (MAP)-containing regions from MAP-free regions within a microtubule, or within microtubule sub-populations. In this method, we measure the MAP-dependent stabilization of microtubule regions to dilution-induced disassembly of the polymer. The appropriate microtubule regions are identified by assembly in the presence of [3H]GTP, and assayed by filter trapping and quantitation of microtubule regions that contain label. We find that MAPs bind very rapidly to polymer binding sites and that they do not exchange from these sites measurably once bound. Also, very low concentrations of MAPs yield measurable stabilization of local microtubule regions. Unlike the stable tubule only polypeptide (STOP) proteins, MAPs do not exhibit any sliding behavior under our assay conditions. These results predict the presence of different stability subclasses of microtubules when MAPs are present in less than saturating amounts. The data can readily account for the observed "dynamic instability" of microtubules through unequal MAP distributions. Further, we report that MAP dependent stabilization is quantitatively reversed by MAP phosphorylation, but that calmodulin, in large excess, has no specific influence on MAP protein activity when MAPs are on microtubules.

scholarly journals Role of non-motile microtubule-associated proteins in virus trafficking

2016 ◽  
Vol 7 (5-6) ◽  
pp. 283-292 ◽  
Author(s):  
Débora M. Portilho ◽  
Roger Persson ◽  
Nathalie Arhel
Keyword(s):  
Motor Proteins ◽  
Current Knowledge ◽  
Cell Entry ◽  
Cellular Transport ◽  
Microtubule Associated Proteins ◽  
Virus Trafficking ◽  
Cytoskeletal Dynamics ◽  
Associated Proteins ◽  
Infected Cells

AbstractViruses are entirely dependent on their ability to infect a host cell in order to replicate. To reach their site of replication as rapidly and efficiently as possible following cell entry, many have evolved elaborate mechanisms to hijack the cellular transport machinery to propel themselves across the cytoplasm. Long-range movements have been shown to involve motor proteins along microtubules (MTs) and direct interactions between viral proteins and dynein and/or kinesin motors have been well described. Although less well-characterized, it is also becoming increasingly clear that non-motile microtubule-associated proteins (MAPs), including structural MAPs of the MAP1 and MAP2 families, and microtubule plus-end tracking proteins (+TIPs), can also promote viral trafficking in infected cells, by mediating interaction of viruses with filaments and/or motor proteins, and modulating filament stability. Here we review our current knowledge on non-motile MAPs, their role in the regulation of cytoskeletal dynamics and in viral trafficking during the early steps of infection.

scholarly journals MAP7 recruits kinesin-1 to microtubules to direct organelle transport

2019 ◽  
Author(s):  
Abdullah R. Chaudhary ◽  
Hailong Lu ◽  
Elena B. Krementsova ◽  
Carol S. Bookwalter ◽  
Kathleen M. Trybus ◽  
...  
Keyword(s):  
Single Molecule ◽  
Organelle Transport ◽  
Microtubule Associated Proteins ◽  
Microtubule Polymerization ◽  
Binding Rate ◽  
Associated Proteins ◽  
Bidirectional Transport ◽  
Directed Motility ◽  
Clear Shift

Microtubule-associated proteins (MAPs) play well-characterized roles in regulating microtubule polymerization, dynamics, and organization. In addition, MAPs control trans-port along microtubules by regulating the motility of kinesin and dynein. MAP7 (ensconsin, E-MAP-115) is a ubiquitous MAP that organizes the microtubule cytoskeleton in mitosis and neuronal branching. MAP7 also promotes the interaction of kinesin-1 with microtubules. We expressed and purified full-length kinesin-1 and MAP7 in Sf9 cells. In single-molecule motiity assays, MAP7 recruits kinesin-1 to microtubules, increasing the frequency of both diffusive and processive runs. Optical trapping assays on beads transported by single and teams of kinesin-1 motors indicate that MAP7 increases the relative binding rate of kinesin-1 and the number of motors simultaneously engaged in ensembles. To examine the role of MAP7 in regulating bidirectional transport, we isolated late phagosomes along with their native set of kinesin-1, kinesin-2, and dynein motors. Bidirectional cargoes exhibit a clear shift towards plus-end directed motility on MAP7-decorated microtubules due to increased forces exerted by kinesin teams. Collectively, our results indicate that MAP7 enhances kinesin-1 recruitment to microtubules and targets organelle transport to the plus end.

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