Engineering Approaches to Biomolecular Motors

Engineering Approaches to Biomolecular Motors: From in vitro to in vivo Poster Abstracts

23-POS Board 23 Contractility Measurements of Calcium-powered Biomotors of the Vorticella Spasmoneme Sangjin Ryu 1 , Eun-gul Chung 2 . 1 University of Nebraska-Lincoln, Lincoln, NE, USA, 2 University of Nebraska-Lincoln, Lincoln, NE, USA. Vorticella is a sessile protist, and its slender stalk anchors the cell body (zooid) on a solid surface. Powered by calcium ions, the contractile organelle spasmoneme coils the stalk in ~5 ms. Thus, the zooid is translated toward the surface at the maximum speed of ~50 mm/s. Because of its ultrafast contraction and unique energy source, the spasmoneme serves as a model organelle for calcium-powered cell motility and biomimetic actuators. The spasmoneme consists of 3-4 diameter fibrils, which appear to be the motor unit composed of the calcium-binding protein, spasmin. These spasmonemal fibrils are thought to coil upon calcium binding due to protein conformation change, leading to the organism-level contraction. Thus, characterizing the spasmonemal motors requires tension measurements of the spasmoneme, and we measured the spasmonemal tension employing engineering approaches. First, we developed computational and theoretical fluid dynamics models of contracting Vorticella , where the zooid was modeled as a sphere moving toward a solid plane following experimentally measured speed profiles of the zooid. Because of the negligible inertia of the zooid, the spasmonemal tension was equated to the zooid drag. The evaluated peak tension ranges 15-50 nN, with a linear dependence on the spasmoneme length. Second, we utilized microfluidic channels to measure the isometric tension. Tethered to the channel surface and laid in the flow, Vorticella showed stalled stalk contractions due to drag on the zooid. Consequently, as the drag increased, the stalk contracted over shorter distances. Therefore, we could estimate the isometric tension to be 100-350 nN, which also shows a linear dependence on the spasmoneme length. Last, based on the measured tension values and their linear dependence on the spasmoneme length, we developed a concenptual model of the spasmoneme and evaluated the contractilty of its motor element.

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