Artificial Forisomes Are Ideal Models of Forisome Assembly and Activity That Allow the Development of Technical Devices

Forisomes are protein polymers found in leguminous plants that have the remarkable ability to undergo reversible muscle-like contractions in the presence of divalent cations and in extreme pH environments. To gain insight into the molecular basis of forisome structure and assembly, we used confocal laser scanning microscopy to monitor the assembly of fluorescence-labeled artificial forisomes in real time, revealing two distinct assembly processes involving either fiber elongation or fiber alignment. We also used scanning and transmission electron microscopy and X-ray diffraction to investigate the ultrastructure of forisomes, finding that individual fibers are arranged into compact fibril bundles that disentangle with minimal residual order in the presence of calcium ions. To demonstrate the potential applications of artificial forisomes, we created :hybrid protein bodies from forisome subunits fused to the B-domain of staphylococcal protein A. This allowed the functionalization of the artificial forisomes with antibodies that were then used to target forisomes to specific regions on a substrate, providing a straightforward approach to develop forisome-based technical devices with precise configurations. The functional contractile properties of forisomes are also better preserved when they are immobilized via affinity reagents rather than by direct contact to the substrate. Artificial forisomes produced in plants and yeast therefore provide an ideal model for the investigation of forisome structure and assembly and for the design and testing of tailored artificial forisomes for technical applications.