scholarly journals A method for multiprotein assembly in cells reveals independent action of kinesins in complex

2014 ◽  
Vol 207 (3) ◽  
pp. 393-406 ◽  
Author(s):  
Stephen R. Norris ◽  
Virupakshi Soppina ◽  
Aslan S. Dizaji ◽  
Kristin I. Schimert ◽  
David Sept ◽  
...  
Keyword(s):  
Molecular Motors ◽  
Intracellular Trafficking ◽  
Intracellular Transport ◽  
Emergent Behavior ◽  
Independent Action ◽  
Dynamic Interactions ◽  
Macromolecular Complexes ◽  
Protein Components ◽  
In Cells

Teams of processive molecular motors are critical for intracellular transport and organization, yet coordination between motors remains poorly understood. Here, we develop a system using protein components to generate assemblies of defined spacing and composition inside cells. This system is applicable to studying macromolecular complexes in the context of cell signaling, motility, and intracellular trafficking. We use the system to study the emergent behavior of kinesin motors in teams. We find that two kinesin motors in complex act independently (do not help or hinder each other) and can alternate their activities. For complexes containing a slow kinesin-1 and fast kinesin-3 motor, the slow motor dominates motility in vitro but the fast motor can dominate on certain subpopulations of microtubules in cells. Both motors showed dynamic interactions with the complex, suggesting that motor–cargo linkages are sensitive to forces applied by the motors. We conclude that kinesin motors in complex act independently in a manner regulated by the microtubule track.

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 Intracellular cargo transport by single-headed kinesin motors

2019 ◽  
Vol 116 (13) ◽  
pp. 6152-6161 ◽  
Author(s):  
Kristin I. Schimert ◽  
Breane G. Budaitis ◽  
Dana N. Reinemann ◽  
Matthew J. Lang ◽  
Kristen J. Verhey
Keyword(s):  
Intracellular Transport ◽  
Motor Coordination ◽  
Optical Trap ◽  
Coiled Coil ◽  
Force Output ◽  
Cellular Assays ◽  
Cellular Events ◽  
Cargo Transport ◽  
In Cells

Kinesin motor proteins that drive intracellular transport share an overall architecture of two motor domain-containing subunits that dimerize through a coiled-coil stalk. Dimerization allows kinesins to be processive motors, taking many steps along the microtubule track before detaching. However, whether dimerization is required for intracellular transport remains unknown. Here, we address this issue using a combination of in vitro and cellular assays to directly compare dimeric motors across the kinesin-1, -2, and -3 families to their minimal monomeric forms. Surprisingly, we find that monomeric motors are able to work in teams to drive peroxisome dispersion in cells. However, peroxisome transport requires minimal force output, and we find that most monomeric motors are unable to disperse the Golgi complex, a high-load cargo. Strikingly, monomeric versions of the kinesin-2 family motors KIF3A and KIF3B are able to drive Golgi dispersion in cells, and teams of monomeric KIF3B motors can generate over 8 pN of force in an optical trap. We find that intracellular transport and force output by monomeric motors, but not dimeric motors, are significantly decreased by the addition of longer and more flexible motor-to-cargo linkers. Together, these results suggest that dimerization of kinesin motors is not required for intracellular transport; however, it enables motor-to-motor coordination and high force generation regardless of motor-to-cargo distance. Dimerization of kinesin motors is thus critical for cellular events that require an ability to generate or withstand high forces.

scholarly journals Palladin Compensates for the Arp2/3 Complex and Supports Actin Structures duringListeriaInfections

mBio ◽  
2018 ◽  
Vol 9 (2) ◽  
Author(s):  
Aaron S. Dhanda ◽  
A. Wayne Vogl ◽  
Sharifah E. Albraiki ◽  
Carol A. Otey ◽  
Moriah R. Beck ◽  
...  
Keyword(s):  
Cell Line ◽  
Structural Integrity ◽  
Comet Tail ◽  
Null Cell ◽  
Free System ◽  
Content Type ◽  
A Cell ◽  
Protein Components ◽  
In Cells

ABSTRACTPalladin is an important component of motile actin-rich structures and nucleates branched actin filament arraysin vitro. Here we examine the role of palladin duringListeria monocytogenesinfections in order to tease out novel functions of palladin. We show that palladin is co-opted byL. monocytogenesduring its cellular entry and intracellular motility. Depletion of palladin resulted in shorter and misshapen comet tails, and when actin- or VASP-binding mutants of palladin were overexpressed in cells, comet tails disintegrated or became thinner. Comet tail thinning resulted in parallel actin bundles within the structures. To determine whether palladin could compensate for the Arp2/3 complex, we overexpressed palladin in cells treated with the Arp2/3 inhibitor CK-666. In treated cells, bacterial motility could be initiated and maintained when levels of palladin were increased. To confirm these findings, we utilized a cell line depleted of multiple Arp2/3 complex subunits. Within these cells,L. monocytogenesfailed to generate comet tails. When palladin was overexpressed in this Arp2/3 functionally null cell line, the ability ofL. monocytogenesto generate comet tails was restored. Using purified protein components, we demonstrate thatL. monocytogenesactin clouds and comet tails can be generated (in a cell-free system) by palladin in the absence of the Arp2/3 complex. Collectively, our results demonstrate that palladin can functionally replace the Arp2/3 complex during bacterial actin-based motility.IMPORTANCEStructures containing branched actin filaments require the Arp2/3 complex. One of the most commonly used systems to study intracellular movement generated by Arp2/3-based actin motility exploits actin-rich comet tails made byListeria. Using these infections together with live imaging and cell-free protein reconstitution experiments, we show that another protein, palladin, can be used in place of Arp2/3 to form actin-rich structures. Additionally, we show that palladin is needed for the structural integrity of comet tails as its depletion or mutation of critical regions causes dramatic changes to comet tail organization. These findings are the first to identify a protein that can functionally replace the Arp2/3 complex and have implications for all actin-based structures thought to exclusively use that complex.

scholarly journals Individual Molecular Motors use Low Forces to bypass Roadblocks during Collective Cargo Transport

2021 ◽  
Author(s):  
Saurabh Shukla ◽  
Alice Troitskaia ◽  
Nikhila Swarna ◽  
Barun Kumar Maity ◽  
Marco Tjioe ◽  
...  
Keyword(s):  
High Throughput ◽  
Molecular Motors ◽  
Intracellular Transport ◽  
Force Sensor ◽  
The Other ◽  
Cargo Transport ◽  
Different Types ◽  
Multicolor Fluorescence ◽  
High Throughput Assay

AbstractA cargo encounters many obstacles during its transport by molecular motors as it moves throughout the cell. Multiple motors on the cargo exert forces to steer the cargo to its destination. Measuring these forces is essential for understanding intracellular transport. Using kinesin as an example, we measured the force exerted by multiple stationary kinesins in vitro, driving a common microtubule. We find that individual kinesins generally exert less than a piconewton (pN) of force, even while bypassing obstacles, whether these are artificially placed 20-100 nm particles or tau, a Microtubule Associated Protein. We demonstrate that when a kinesin encounters an obstacle, the kinesin either becomes dislodged and then re-engages or switches protofilaments while the other kinesins continue to apply their (sub-)pN forces. By designing a high-throughput assay involving nanometer-resolved multicolor-fluorescence and a force-sensor able to measure picoNewtons of force, our technique is expected to be generally useful for many different types of molecular motors.

scholarly journals Microtubule architecture in vitro and in cells revealed by cryo-electron tomography

2018 ◽  
Vol 74 (6) ◽  
pp. 572-584 ◽  
Author(s):  
Joseph Atherton ◽  
Melissa Stouffer ◽  
Fiona Francis ◽  
Carolyn A. Moores
Keyword(s):  
Molecular Motors ◽  
Electron Tomography ◽  
Three Dimensional ◽  
Structural Heterogeneity ◽  
Dimensional Structure ◽  
Cellular Functions ◽  
Cellular Processes ◽  
Cryo Electron Tomography ◽  
In Cells

The microtubule cytoskeleton is involved in many vital cellular processes. Microtubules act as tracks for molecular motors, and their polymerization and depolymerization can be harnessed to generate force. The structures of microtubules provide key information about the mechanisms by which their cellular roles are accomplished and the physiological context in which these roles are performed. Cryo-electron microscopy allows the visualization of in vitro-polymerized microtubules and has provided important insights into their overall morphology and the influence of a range of factors on their structure and dynamics. Cryo-electron tomography can be used to determine the unique three-dimensional structure of individual microtubules and their ends. Here, a previous cryo-electron tomography study of in vitro-polymerized GMPCPP-stabilized microtubules is revisited, the findings are compared with new tomograms of dynamic in vitro and cellular microtubules, and the information that can be extracted from such data is highlighted. The analysis shows the surprising structural heterogeneity of in vitro-polymerized microtubules. Lattice defects can be observed both in vitro and in cells. The shared ultrastructural properties in these different populations emphasize the relevance of three-dimensional structures of in vitro microtubules for understanding microtubule cellular functions.

scholarly journals Self-repair protects microtubules from their destruction by molecular motors:

2018 ◽  
Author(s):  
Sarah Triclin ◽  
Daisuke Inoue ◽  
Jeremie Gaillard ◽  
Zaw Min Htet ◽  
Morgan De Santis ◽  
...  
Keyword(s):  
Chromosome Segregation ◽  
Molecular Motors ◽  
Intracellular Transport ◽  
Atp Hydrolysis ◽  
Low Energy ◽  
Mechanical Work ◽  
Repair Mechanism ◽  
Tubulin Dimer ◽  
Self Repair

Microtubules are dynamic polymers that are used for intracellular transport and chromosome segregation during cell division. Their instability stems from the low energy of tubulin dimer interactions, which sets the growing polymer close to its disassembly conditions. Microtubules function in coordination with kinesin and dynein molecular motors, which use ATP hydrolysis to produce mechanical work and move on microtubules. This raises the possibility that the forces produced by walking motors can break dimer interactions and trigger microtubule disassembly. We tested this hypothesis by studying the interplay between microtubules and moving molecular motors in vitro. Our results show that the mechanical work of molecular motors can remove tubulin dimers from the lattice and rapidly destroy microtubules. This effect was not observed when free tubulin dimers were present in the assay. Using fluorescently labelled tubulin dimers we found that dimer removal by motors was compensated for by the insertion of free tubulin dimers into the microtubule lattice. This self-repair mechanism allows microtubules to survive the damage induced by molecular motors as they move along their tracks. Our study reveals the existence of coupling between the motion of kinesin and dynein motors and the renewal of the microtubule lattice.

scholarly journals A FLIC motility assay reveals myosin-6 coordination limited by actin filament buckling

2016 ◽  
Author(s):  
Agata K. Krenc ◽  
Jagoda J. Rokicka ◽  
Ronald S. Rock
Keyword(s):  
Actin Cytoskeleton ◽  
Actin Filament ◽  
Molecular Motors ◽  
Intracellular Transport ◽  
Motor Coordination ◽  
Contrast Microscopy ◽  
Interference Contrast Microscopy ◽  
Myosin Motors ◽  
Unique Application

ABSTRACTTeams of myosin motors carry out intracellular transport and contract the actin cytoskeleton. To fully understand the behavior of multi-myosin ensembles we need to know the properties of individual myosins and the mode of interaction between them. Current models of the interactions within the myosin complex treat the actin filament as a stiff rod, not contributing to the regulation of collective myosin dynamics. Here, we present data suggesting that force transduction through the actin filament is an important element of interaction within myosin-6 ensembles in vitro. Multiple myosin-6s coordinate their steps if they are separated by a short (and therefore high-force bearing) segment of actin. The measurements were performed using Fluorescence Interference Contrast Microscopy (FLIC) to measure small changes in the height of fluorescently labeled actin. Using FLIC, we assign the positions of myosins in a gliding filament assay geometry and measure their attachment time to actin. We also identify actin segments that are buckled or under tension. We show that myosin-6 holds actin about 10 nm above the surface. However, due to asynchronous myosin stepping, frequent buckles up to about 60 nm high appear. The buckle lifetime decreases as the distance between the myosin-6s is reduced, a sign of inter-motor coordination. Our data are consistent with coordinated stepping of closely spaced myosins, but uncoordinated motility with widely separated myosins where buckles can form. These features would be expected to operate on myosins in the cell, where motor spacing may vary considerably depending on the target organelle.SIGNIFICANCE STATEMENTMyosins are molecular motors that carry out intracellular transport. Interactions between the myosins are crucial for understanding their function. Using Fluorescence Interference Contrast (FLIC) microscopy we characterized the interaction between multiple myosin-6 motors immobilized to the surface of a slide and pulling the same actin filament. Our results point towards coordination of myosin steps as a mechanism governing the behavior of a multi-myosin complex. We also demonstrated the unique application of FLIC microscopy for highly parallel identification and measurement of single myosin motors in a gliding filament format. These features of FLIC enable a robust study of collective myosin dynamics.

scholarly journals Modelling cytoskeletal transport by clusters of non-processive molecular motors with limited binding sites

2020 ◽  
Vol 7 (8) ◽  
pp. 200527
Author(s):  
Naruemon Rueangkham ◽  
Ian D. Estabrook ◽  
Rhoda J. Hawkins
Keyword(s):  
Molecular Motors ◽  
Binding Sites ◽  
Intracellular Transport ◽  
Exclusion Process ◽  
Stochastic Simulations ◽  
Published Data ◽  
Analytical Work ◽  
Number Of Binding Sites

Molecular motors are responsible for intracellular transport of a variety of biological cargo. We consider the collective behaviour of a finite number of motors attached on a cargo. We extend previous analytical work on processive motors to the case of non-processive motors, which stochastically bind on and off cytoskeletal filaments with a limited number of binding sites available. Physically, motors attached to a cargo cannot bind anywhere along the filaments, so the number of accessible binding sites on the filament should be limited. Thus, we analytically study the distribution and the velocity of a cluster of non-processive motors with limited number of binding sites. To validate our analytical results and to go beyond the level of detail possible analytically, we perform Monte Carlo latticed based stochastic simulations. In particular, in our simulations, we include sequence preservation of motors performing stepping and binding obeying a simple exclusion process. We find that limiting the number of binding sites reduces the probability of non-processive motors binding but has a relatively small effect on force–velocity relations. Our analytical and stochastic simulation results compare well to published data from in vitro and in vivo experiments.

MiR-485-5p Promotes Neuron Survival through Mediating Rac1/Notch2 Signaling Pathway after Cerebral Ischemia/Reperfusion

2020 ◽  
Vol 17 (3) ◽  
pp. 259-266 ◽  
Author(s):  
Xuan Chen ◽  
Sumei Zhang ◽  
Peipei Shi ◽  
Yangli Su ◽  
Dong Zhang ◽  
...  
Keyword(s):  
Oxidative Stress ◽  
Cell Viability ◽  
Therapeutic Option ◽  
Ischemia Reperfusion ◽  
Glucose Deprivation ◽  
Small Gtpase ◽  
Luciferase Reporter ◽  
Pathological Feature ◽  
In Cells

Objective: Ischemia-reperfusion (I/R) injury is a pathological feature of ischemic stroke. This study investigated the regulatory role of miR-485-5p in I/R injury. Methods: SH-SY5Y cells were induced with oxygen and glucose deprivation/reoxygenation (OGD/R) to mimic I/R injury in vitro. Cells were transfected with designated constructs (miR-485- 5p mimics, miR-485-5p inhibitor, lentiviral vectors overexpressing Rac1 or their corresponding controls). Cell viability was evaluated using the MTT assay. The concentrations of lactate dehydrogenase, malondialdehyde, and reactive oxygen species were detected to indicate the degree of oxidative stress. Flow cytometry and caspase-3 activity assay were used for apoptosis assessment. Dual-luciferase reporter assay was performed to confirm that Rac family small GTPase 1 (Rac1) was a downstream gene of miR-485-5p. Results: OGD/R resulted in decreased cell viability, elevated oxidative stress, increased apoptosis, and downregulated miR-485-5p expression in SH-SY5Y cells. MiR-485-5p upregulation alleviated I/R injury, evidenced by improved cell viability, decreased oxidative markers, and reduced apoptotic rate. OGD/R increased the levels of Rac1 and neurogenic locus notch homolog protein 2 (Notch2) signaling-related proteins in cells with normal miR-485-5p expression, whereas miR- 485-5p overexpression successfully suppressed OGD/R-induced upregulation of these proteins. Furthermore, the delivery of vectors overexpressing Rac1 in miR-485-5p mimics-transfected cells reversed the protective effect of miR-485-5p in cells with OGD/R-induced injury. Conclusion: This study showed that miR-485-5p protected cells following I/R injury via targeting Rac1/Notch2 signaling suggest that targeted upregulation of miR-485-5p might be a promising therapeutic option for the protection against I/R injury.

Biologic Aspects of Expression of Stably Integrated Transgenes in Cells of the Skin In Vitro and In Vivo

1999 ◽  
Vol 111 (3) ◽  
pp. 198-205 ◽  
Author(s):  
Gerald G. Krueger ◽  
Jeffery R. Morgan ◽  
Marta J. Petersen
Keyword(s):  
In Cells
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