Integrating biochemical and physical mechanisms of actin and Major Sperm Protein-driven propulsion

Cell migration is driven by the polymerization of cytoskeletal proteins into filaments that push out the leading edge of the cell by a biochemically and biophysically complex process. The goal of our research is to provide an integrated picture of how the biochemical activities of cytoskeletal proteins affect individual filament mechanics and overall network properties to produce useful force and movement.

We will study two cytoskeletal protein machineries: actin of eukaryotic cells and Major Sperm Protein (MSP) of Caenorhabditis elegans sperm cells. Both machineries have very similar functionalities in terms of motile force and velocity, yet actin and MSP have different biochemical properties (sequence, structure, interaction partners) and thus likely different biophysical properties (mechanical stiffness and strength). By comparing these two very different cytoskeletal systems that have identical roles in cell movement, we hope to define the universal biochemical and physical properties governing cell motility.

To achieve this goal, we have assembled an interdisciplinary team that includes experts in actin and MSP biochemistry and in biopolymer mechanics on both the single filament and collective network scales. On the one hand, we will use biochemical manipulation and in vitro motility assays to test how biochemical regulation affects actin- and MSP-driven propulsion. The physical repercussions of biochemical tuning will be investigated by microrheology and scanning probe microscopy to measure the forces generated by polymerizing actin and MSP filaments and their elastic properties. For actin, we will focus on how certain domains and phosphorylation states of the Drosophila Enabled/Vasodilator-stimulated Phosphoprotein (Ena/VASP) family affect movement. The Ena/VASP proteins are key players in cell motility, but have been little studied from a mechanical point of view. For MSP, we will establish for the first time a purely in vitro motility assay and use this set-up to study MSP-associated factors that will be identified during the course of this project. This will be the first detailed biochemical/biophysical study of this propulsion system in the model organism C. elegans.

Ultimately protein chemistry and mechanical properties will be integrated into a complete description of cell movement in the context of two very different cytoskeletal systems.