CAREER: Biomechanics of Polymerization Motors and Cell Motility

University Of California-Berkeley, Berkeley CA

Investigators

Abstract

0348758 Fletcher Many cell movements and shape changes depend on the cell's ability to internally generate and control mechanical forces. Directed cell movement is fundamental to both maintenance of health and spread of diseases within the body. Polymerization of the cytoskeletal protein actin into networks of filaments - like the expansion of a linear piezoelectric actuator upon charging - creates directed forces that extend the cell's leading edge and play a fundamental role in guiding cell motility. This CAREER proposal focused on a key biomechanical question in cell motility: how does actin polymerization, sometimes described as a polymerization motor, generate force? Answering this question will help reveal the mechanical mechanisms underlying cell motility and its role in disease.. Future development of mechanical measurement techniques for studying force-generating cellular "subsystems" may lead to new strategies for drug discovery that target specific mechanical processes and novel sensors and actuators based on biological building blocks. The proposed research plan investigates the biomechanics of polymerization motors through (i) instrument development, (ii) in vitro experimentation, and (iii) cell motility modeling and measurement. Atomic force microscopy is an increasingly popular tool for biomechanical studies of cells, but commercial instruments are not appropriate for measuring polymerization forces over biologically relevant timescales. This work develops a differential force microscopy technique to directly measure actin polymerization rates and stall forces. Using an in vitro motility system based on the bacterial pathogen Listeria monocytogenes, experiments will determine the effect of nucleation surface geometry and accessory protein concentration on polymerization dynamics. Finally, results from the experiments will be compared to predictions from existing models of actin-based motility and used to investigate differences in the cell motility speeds and forces of normal and cancerous cells. The proposed education plan provides learning opportunities for current and future researchers in the mechanics of cell movement through (i) course development, (ii) a mechanical property database, and (iii) hands-on experiments. The PI will develop and teach a new course on the mechanics of molecules in the Bioengineering Department at UC Berkeley that emphasizes the role of mechanical properties of proteins in cell movements and the spread of disease. A web-based database of the mechanical properties of proteins and other macromolecules will be created to provide researchers in the field with an organized summary of the currently known mechanical properties for use in motility models and comparisons. To motivate the next generation of scientists and engineers, the PI will work with undergraduate student groups to create hands-on microscopy experiments for Oakland, CA elementary school children introducing them to cell movements through microscopy activities with single-celled organisms.