Studying Motor-Free Motility in Synthetic Cells

Ciliated protists are single celled eukaryotic organisms with a striking particularity – some of them display the fastest motions in the biological world! The mechanism that enables such phenomenon is a motor-free, calcium-based cytoskeletal system. Unlike the actin-myosin based cytoskeletons, ATP is not directly consumed; a local increase in cytosolic Ca²⁺ concentration is what triggers the contraction. In this project, we aim to study the mechanical effects of calcium-based motor-free contraction in the cellular membrane, and how the interplay between these two elements allows cell motility.

We study this system by using a bottom-up approach: we are going to build a synthetic contractile system inside of a cell-sized liposome, which mimics the structure and composition of a cellular membrane. The main component of our is tetrahymena calcium-binding protein 2 (tcb2), the main component of Tetrahymena termophila cytoskeleton that shows calcium-dependent contractile behavior. In order to create a controlled artificial calcium increase within the liposome, we incorporate a compound that chelates calcium and releases it upon irradiation with UV light. The method of choice for assembling the synthetic cells is cDICE (Continuous Interface Crossing Encapsulation). The results display that we are able to trigger the contraction of the protein network inside the liposomes by using light, from which we quantify the speed of contraction and the membrane deformations that arise from it.

The study of motor-free cytoskeletons is important in the context of bioengineering, since it opens new venues for the design of more energetically efficient systems and devices. The ability to optically control calcium signaling pathways is also a rising field in biomedicine, which has already offered solutions for diagnosis and treatment of various diseases, including cancer, and several muscular and neurological disorders. The convergence of these two disciplines in the presented work will contribute to building a solid ground for the development of the next generation of optically-controlled bioactuators and biosensing devices.