Otro
Ring coupler moving via a biased-diffusion mechanism [Microtubule depolymerization as a biological machine]
Autor
Efremov, Artem
Grishchuk, Ekaterina L.
McIntosh, J. Richard
Ataullakhanov, Fazly I.
Resumen
This video shows a shortening microtubules end 'Depolymerizing microtubule' and a ring coupler (red), which was modeled after the Dam1/DASH kinetochore complex from budding yeast. Each ring subunit binds to the middle of the outer surface of beta-tubulin with a flexible linker 4 nm in length (blue). This calculation shows a ring with 13 subunits, but the rings with more subunits are expected to behave similarly because the number of bonds that the ring can establish with the microtubule wall is determined by the symmetry of the microtubule lattice (13-fold). In this calculation, the energy of interaction between each linker and tubulin is low (3 kBT, where kB is Boltzmann constant) relative to the thermal energy, so the ring diffuses rapidly on the MT wall (the video stops when the ring moves beyond the microtubule segment that was used for this calculation). As the plus end of the microtubule disassembles, the ring's displacements become biased, i.e. they occur on average away from the shortening end and towards the bottom of the screen. This is because the ring motion in the opposite direction is interrupted by a mechanical barrier formed by the flared protofilaments. The energy necessary to straighten protofilaments is so high that the ring's thermal energy is not sufficient to pass this barrier. Although technically, the bending protofilaments push on the weakly bound ring when it comes in contact, this aspect of their interactions is mechanically insignificant, due to the low resistance of ring sliding. As a result, such a ring is expected to have no impact on the rate at which the microtubule shortens Componente Curricular::Educação Superior::Ciências Biológicas::Morfologia