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

, Eun-gul Chung

University of Nebraska-Lincoln, Lincoln, NE, USA,

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.