|Michael Knoblauch1, Gundula A. Noll1, Dörte Scharner1, Dirk Prüfer2, Aart van Bel1, and Winfried S. Peters3
1Institute for General Botanics and Plant Physiology, Department of Biology, Justus-Liebig-University, Senckenbergstr. 17-21, D-35390 Gießen, Germany,
Emerging technologies create a growing demand for 'intelligent materials' that can perform mechanic work at the macro- down to the nanometre scale. Synthetic contractile electrochemomechanical polymers, so-called 'artificial muscles', respond to pH, electrical fields, or ionic conditions. However, biomimetic materials such as mechanically active proteins attract increasing interest because of their variable composition that invites molecular engineering, and because of their potential for self-assembly. Here we report the unexpected discovery of contractility in protein bodies from higher plant conducting tissues. These so-called crystalline P-proteins represent a novel class of mechanoproteins. They contract and expand reversibly in dependence of the free concentration of Ca2+, but are distinct from spasmonemes, another type of divalent cation-controlled mechanoproteins. While contraction as such seems unlikely to be part of their biological function, crystalline P-proteins possess unique properties that let them appear promising prototypes for biomimetic actuators in micro- and nano-devices.