Biology subjects

Portran, D.

Publications and source records attributed to Portran, D..

4 recordsLinked to original sources

bioRxiv2025

Control of mitotic spindle disassembly through SUMO-targeted ubiquitylation of yeast kinesin-5

Faithful cell division requires precise control of spindle assembly and disassembly. In budding yeast, spindle breakdown at mitotic exit depends on Cdk1 inactivation and ubiquitin-mediated degradation of spindle stabilizing factors, including the kinesin-5 Cin8 and the crosslinker Ase1/PRC1. Timely degradation of Cin8 by APCCdh1 prevents spindle over-elongation and deformation. We have identified SUMOylation and the SUMO-targeted ubiquitin ligase Slx5 as regulators of spindle disassembly. Cin8 is SUMOylated and interacts with Slx5, suggesting that it is a substrate of Slx5. Deletion of the SLX5 gene or expression of a SUMOylation-defective Cin8 mutant cause spindle disassembly defects that resemble those of degradation-resistant Cin8 mutants. Reduction of Cin8 SUMOylation partly stabilizes spindles in ase1{Delta} cells. In addition, SUMOylation of Cin8 and Slx5 are required for timely actomyosin-ring contraction and Cin8 clearance from the mitotic spindle. We propose that SUMOylation regulates Cin8 activity and that SUMO-targeted ubiquitylation facilitates removal Cin8 from the spindle, promoting spindle disassembly at the end of mitosis.

cell biology↗

bioRxiv2024

The kinesin Kip2 promotes microtubule growth using a bipartite polymerase module to deliver tubulin to microtubule plus-ends

Kinesin molecular motors are essential for fundamental cellular processes such as chromosome segregation or vesicular transport. To fulfil their function, some kinesins promote microtubule growth, but the molecular mechanism underlying this activity remains unclear. One of the motors with the strongest microtubule growth-promoting activity is Kip2, a kinesin that is required for astral microtubule integrity and spindle positioning in yeast. Here we show that the ability of Kip2 to polymerize microtubules is coupled to binding and transport of free tubulin. We report that the Kip2 N-terminus is required to promote microtubule elongation in vitro and in vivo. Kip2 binds free tubulin through this unstructured, basic domain and delivers it to microtubule plus-ends. In addition to the N-terminus, we find that ATP hydrolysis and motor activity is also required for microtubule polymerisation. Finally, transfer of the Kip2 N-terminus to kinesin-1, a kinesin that lacks polymerase activity, transforms kinesin-1 into a tubulin-transporting microtubule polymerase. We propose that motor-driven tubulin delivery to microtubule plus-ends is an efficient mechanism used by kinesins to promote microtubule polymerization.

cell biology↗

bioRxiv2019

Effects of α-tubulin acetylation on microtubule structure and stability

Acetylation of K40 in -tubulin is the sole post-translational modification to mark the luminal surface of microtubules. It is still controversial whether its relationship with microtubule stabilization is correlative or causative. We have obtained high-resolution cryo-electron microscopy reconstructions of pure samples of TAT1-acetylated and SIRT2-deacetylated microtubules to visualize the structural consequences of this modification and reveal its potential for influencing the larger assembly properties of microtubules. We modeled the conformational ensembles of the unmodified and acetylated states by using the experimental cryo-EM density as the structural restraint in molecular dynamics simulations. We found that acetylation alters the conformational landscape of the flexible loop that contains K40. Modification of K40 reduces the disorder of the loop and restricts the states that it samples. We propose that the change in conformational sampling that we describe, at a location very close to the lateral contacts site, is likely to affect microtubule stability and function.

biophysics↗

bioRxiv2018

Self-repair protects microtubules from their destruction by molecular motors

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.

cell biology↗