Dresden 2026 – scientific programme

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BP: Fachverband Biologische Physik

BP 9: Single Molecule Biophysics

BP 9.4: Talk

Monday, March 9, 2026, 17:45–18:00, BAR/0205

Direct measurement of ultra-weak plant kinesin steps using silicon nanospheres as optical tweezers probes — •Aleksandr Kostarev¹, Shu Yao Leong¹, Anita Jannasch¹, Minoru Fujii², Hiroshi Sugimoto², and Erik Schäffer¹ — ¹Eberhard Karls Universität Tübingen, Tübingen, Germany — ²Kobe University, Kobe, Japan

Kinesin motor proteins are essential for transport along cytoskeletal microtubules and cell division. In plants, cytokinesis relies on phragmoplast orienting kinesins (POKs). The kinesin-12 paralog POK2 can generate only about 300 fN of force. This low force is consistent with the idea that POK2 does not transport cargo, similar to weak kinesin-8 motors, the function of which is unknown in plants. To understand the function and mechanochemistry of these ultra-weak motors, it is necessary to detect their individual steps during ATP hydrolysis. However, the spatiotemporal resolution achieved with conventional probes in optical tweezers is insufficient for detecting fast steps at such low forces. To overcome this limitation, we used high refractive-index silicon nanospheres for optical trapping. With these nanospheres, we achieved an unprecedented force resolution of 60 aN at room temperature in liquids with a force sensitivity of 2.7 fN Hz^(-1/2). We bound single POK2 or plant kinesin-8 motors to the nanospheres and were able to detect individual 8-nm steps with 4-nm substeps within a force range of 100-400 fN. These in vitro measurements establish a path toward identifying plant kinesin function and demonstrate the potential of silicon nanospheres for studying ultra-weak molecular machines.

Keywords: Optical tweezers; Silicon nanospheres; Kinesins; Force measurements; Attonewton resolution