F-actin Architecture Determines the Conversion of Chemical Energy into Mechanical Work

Many biological processes utilize the actin cytoskeleton to perform mechanical work in the cells.  The actin cytoskeleton is comprised of F-actin, myosin, and other actin-binding proteins, which can assemble into large-scale architectures.  There has been significant investigation of how these structures promote force generation, yet the impact of different F-actin architecture on the conversion of chemical energy to mechanical work is still not well defined.  Work by Sakamoto and Murrell sought to explain how these different F-actin structures impact myosin energy consumption during mechanical work.  In order to study different F-actin architectures in a precise manner, the group utilized an in vitro approach where specific nucleators and crosslinkers could be added.  This approach was combined with an NADH-coupled assay to measure ATP consumption.  The combined system was then placed within an oil-in-water droplet environment, which allowed them to monitor both contractile forces and ATP consumption simultaneously.  The model system was validated by altering ATP levels or through Myosin inhibition with Blebbstatin.  The group next utilized this model system and tested a variety of actin architectures and found that mixed polarity bundles interfered with network contraction while decelerating ATP consumption, while other architectures like branched networks showed high ATP consumption without measurably large network contraction.  Linear F-actin architecture resulted in significant contractile forces and high ATP consumption.  Ultimately, this study illuminated how F-actin architecture has a profound effect on both force generation and energy consumption rates during mechanical work.   Several of Cytoskeleton Inc.’s actin tools including Rhodamine Actin Protein (Cat. # AR05), Myosin II Protein (Cat. # MY02), ARP 2/3 Protein Complex (Cat. # RP01P), and many others were used throughout this study to create the in vitro actin architectures.