Biology subjects

Lansky, Z.

Publications and source records attributed to Lansky, Z..

23 records · Page 2Linked to original sources

bioRxiv2020

Nanoscopic Structural Fluctuations of Disassembling Microtubules Revealed by Label-Free Super-Resolution Microscopy

Microtubules are cytoskeletal polymers of tubulin dimers assembled into protofilaments that constitute nanotubes undergoing periods of assembly and disassembly. Static electron micrographs suggest a structural transition of straight protofilaments into curved ones occurring at the tips of disassembling microtubules. However, these structural transitions have never been observed and the process of microtubule disassembly thus remains unclear. Here, a label-free optical microscopy capable of selective imaging of the transient structural changes of protofilaments at the tip of a disassembling microtubule is introduced. Upon induced disassembly, the transition of ordered protofilaments into a disordered conformation is resolved at the tip of the microtubule. Imaging the unbinding of individual tubulin oligomers from the microtubule tip reveals transient pauses and relapses in the disassembly, concurrent with enrichment of ordered protofilament segments at the microtubule tip. These findings show that microtubule disassembly is a discrete process and suggest a mechanism of switching from the disassembly to the assembly phase.

biophysics↗

bioRxiv2020

Intrinsically disordered domain of kinesin-3 Kif14 enables unique functional diversity

In addition to their force-generating motor domains, kinesin motor proteins feature various accessory domains enabling them to fulfil a variety of functions in the cell. Human kinesin-3, Kif14, localizes to the midbody of the mitotic spindle and is involved in the progression of cytokinesis. The specific motor properties enabling Kif14s cellular functions, however, remain unknown. Here, we show in vitro that it is the intrinsically disordered N-terminal domain of Kif14 that enables unique functional diversity of the motor. Using single molecule TIRF microscopy we observed that the presence of the disordered domain i) increased the Kif14 run-length by an order of magnitude, rendering the motor super-processive and enabling the motor to pass through highly crowded microtubule areas shielded by cohesive layers of microtubule-associated protein tau, which blocks less processive motors ii) enabled robust, autonomous Kif14 tracking of growing microtubule tips, independent of microtubule end-binding (EB) proteins and iii) enabled Kif14 to crosslink parallel microtubules and to drive the relative sliding of antiparallel ones. We explain these features of Kif14 by the observed increased affinity of the disordered domain for GTP-like tubulin and the observed diffusible interaction of the disordered domain with the microtubule lattice. We hypothesize that the disordered domain tethers the motor domain to the microtubule forming a diffusible foothold. We suggest that the intrinsically disordered N-terminal anchoring domain of Kif14 is a regulatory hub supporting the various cellular functions of Kif14 by tuning the motors interaction with microtubules.

biophysics↗

bioRxiv2020

Anillin propels myosin-independent constriction of actin rings

Constriction of the actin cytokinetic ring is an essential step of cell division. In a generally accepted view, the constriction is driven by relative sliding of actin filaments propelled by myosin motors. However, in multiple organisms, the ring constriction is myosin independent. How actin rings constrict in the absence of motor activity remains unclear. Here, we demonstrate that actin contractility can be propelled by anillin, a diffusible non-motor actin crosslinker, localising to the cytokinetic ring. We in vitro observed the formation and constriction of rings comprising multiple actin filaments bundled by anillin. Rings constricted due to anillin-generated forces maximising the overlap lengths between the filaments. Actin disassembly promoted constriction. We propose that actin crosslinkers, generating forces complementary to molecular motors, contribute to the contractility of diverse actin structures, including the cytokinetic ring.

cell biology↗

bioRxiv2020

Mitochondria-adaptor TRAK1 promotes kinesin-1 driven transport in crowded environments

Intracellular trafficking of organelles, driven by kinesin-1 stepping along microtubules, underpins essential processes including neuronal activity. In absence of other proteins on the microtubule surface, kinesin-1 performs micron-long runs. Under protein crowding conditions, however, kinesin-1 motility is drastically impeded. It is thus unclear how kinesin-1 acts as an efficient transporter in crowded intracellular environments. Here, we demonstrate that TRAK1 (Milton), an adaptor protein essential for mitochondrial trafficking, activates kinesin-1 and increases its robustness of stepping in protein crowding conditions. Interaction with TRAK1 i) facilitated kinesin-1 navigation around obstacles, ii) increased the probability of kinesin-1 passing through cohesive envelopes of tau and iii) increased the run length of kinesin-1 in cell lysate. We explain the enhanced motility by the observed direct interaction of TRAK1 with microtubules, providing an additional anchor for the kinesin-1-TRAK1 complex. We propose adaptor-mediated tethering as a mechanism regulating kinesin-1 motility in various cellular environments.

cell biology↗

bioRxiv2018

Kinetically distinct phases of tau on microtubules regulate kinesin motors and severing enzymes

Tau is an intrinsically disordered protein, which diffuses on microtubules. In neurodegenerative diseases collectively termed tauopathies, tau malfunction and its detachment from axonal microtubules is correlated with microtubule degradation. It is known that tau can protect microtubules from microtubule-degrading enzymes, such as katanin. However, how tau can fulfill such regulative function is still unclear. Using in vitro reconstitution, we here show that tau molecules on microtubules cooperatively form islands of an ordered layer with regulatory qualities distinct from a comparably dense layer of diffusible tau. These islands shield the microtubules from katanin and kinesin-1 but are penetrable by kinesin-8 which causes the islands to disassemble. Our results indicate a new phase of tau, constituting an adjustable protective sheath around microtubules.

biophysics↗