Controlled Mechanical Actuation of Adsorbed Forisome Mechanoproteins: A Step Toward Biomolecular Devices

Forisomes are giant structural plant mechanoproteins that reversibly undergo a transition from a longitudinally expanded to a contracted (dispersed) state. This transition is driven by a change in the concentration of Ca2+ ions. Artificial forisomes, expressed in yeast, have a width of 0.7 µm and a length of 4.6 µm and adsorb onto a gold surface. Scanning electrochemical microscopy imaging of the adsorbed forisomes reveales a heterogenous film in which several proteins adsorb together on the substrate surface. The adsorbed forisomes maintain their biological activity and undergo reversible contraction–expansion reactions. Infrared spectroscopy (IRS) shows that Ca2+ ions are coordinated to the carboxylate groups in the side chains of Asp and Glu affecting the 3D arrangement of the corresponding protein fragments allowing for a longitudinal contraction, dispersion of the forisome volume, and water uptake. In films, expanded forisomes accumulate small ions (ethylendiaminetetraacetic acid dianion or [Fe(CN)6]4-) that are released upon Ca2+ driven dispersion. The properties described here make forisomes attractive for biotechnological applications.