Berlin 2018 – wissenschaftliches Programm

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BP: Fachverband Biologische Physik

BP 33: Cytoskeletal Filaments II

BP 33.1: Vortrag

Donnerstag, 15. März 2018, 15:00–15:15, H 1028

High resolution three-dimensional tracking with optical tweezers reveals protofilament switching of the kinesin-8 Kip3 — •Michael Bugiel and Erik Schäffer — Zentrum für Molekularbiologie der Pflanzen (ZMBP), Universität Tübingen, Auf der Morgenstelle 32, 72076 Tübingen, Germany

The budding yeast kinesin-8 Kip3 is a highly processive motor protein that walks to the ends of cytoskeletal microtubules and shortens them in a collective manner. Microtubules consist of circularly arranged tubulin polymer chains, called protofilaments. How exactly Kip3 reaches the end is unclear. Left-handed rotations of microtubules in Kip3 gliding assays indicated sideward motion of Kip3 perpendicular to the microtubule axis, i.e. switching between single protofilaments. We used high resolution optical tweezers in a force-feedback mode to track the trajectories of single Kip3 motors. Previous 2D assays with alternating sideward loads showed that Kip3 performs sideward steps in both directions, consistent with a diffusive sideward motion on the microtubule lattice. Here, we topographically suspended microtubules such that Kip3-coated microspheres can freely rotate around the microtubules in three dimensions. Tracking these motor driven microspheres with a 3D, zero-load force-clamp showed that Kip3 switched protofilaments in discrete steps equally frequent in both directions. A statistical analysis confirmed a diffusive sideward motion of Kip3, consistent with the 2D results. The diffusive protofilament switching may enable Kip3 to bypass obstacles and reach the microtubule end for length regulation.