Measurement of Forces Generated by Chemomechanical Protein Aggregates Using Polymer BioMEMS
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Measurement of Forces Generated by Chemomechanical Protein Aggregates Using Polymer BioMEMS Nicholas Ferrell1, Stefan Schwan2,3, Uwe Spohn2, Andreas Heilmann2, and Derek Hansford1 1 Department of Biomedical Engineering, Ohio State University, 1080 Carmack Rd., 270 Bevis Hall, Columbus, OH, 43210 2 Biological Materials and Interfaces, Fraunhofer Institute for Mechanics of Materials Halle, Walter-Hülse-Strasse 1, Halle / Saale, 06120, Germany 3 Translational Centre for Regenerative Medicine, Universität Leipzig, Leipzig, 04103, Germany ABSTRACT P-protein bodies (forisomes), found in the phloem tissue of legumes, transform the chemical free energy of their reaction with alkaline earth metal ions into mechanical energy. Micromechanical forces generated by the switching of forisomes in aqueous solutions were measured by monitoring the bending of microscale polymer cantilever beams. The forisomes were adsorbed to the tips of four orthogonal beams of a BioMEMS microsystem that was manufactured using the process of sacrificial layer micromolding. The sensor layout allows force measurements in the longitudinal and radial direction of the forisomes. Measurements were performed on eight different forisomes. Longitudinal forces ranged from 84-136 nN with an average of 117 ± 19 nN (± standard deviation) and radial forces were 22-61 nN (44 ± 13 nN). INTRODUCTION Chemomechanically active protein aggregates in plants, e.g. the p-protein bodies (forisomes) in phloem cells of legumes, transform the chemical free energy of their reaction with alkaline earth ions into mechanical energy [1,2]. Unlike most other motor proteins, the action of these chemomechanical protein aggregates does not rely on adenosine triphosphate (ATP) to supply the energy for actuation. One possible mechanism of a conformational change in the protein structure was described in [3]. It was suggested that the protonation/deprotonation of amino and carboxylate groups and the formation of metal-protein complexes result in a change in the folding state for at least a part of the aggregated protein molecules. The stability of repeated energy conversions depends on the concentration of dissolved oxygen and can be considerably improved by working under anaerobic conditions. Due to the reaction with Ca2+, Sr2+or Ba2+ ions, the protein aggregates contract by 10%40% of their original length and increase their cross sectional diameter by as much as 180%. The proposed thermodynamic cycling process [4] leading back to the initial state (longitudinally stretched forisome) can be completed by the extraction of these ions with ethylene diaminetetraacetic acid (EDTA) under anaerobic conditions. Scanning electron microscopy (SEM) investigations have demonstrated that the spindleshaped bodies with sizes between 25 and 40 µm consist of fiber bundle units which change their length and diameter in a cooperative manner during the switching between the longitudinally stretched and the contracted states. Previously, it was shown that the longitudinal contraction forces are
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