Polymer-Carrying Ability of Actin Filaments Interacting with Myosin Motors in a Biological Motility System In Vitro.

Abstract

The reconstituted motility system of actin-myosin is expected to be used in bioinspired transport devices, in which carried materials are attached to either moving actin filaments or walking myosin molecules. However, the dependence of the ability to transport on the size of the attached materials is still inadequately understood. Here, as carried materials, polyethylene glycols (PEGs) of various sizes are covalently bound to actin filaments, and the motility of PEG-attached filaments on a heavy meromyosin (HMM) immobilized on a glass surface is observed via fluorescence microscopy. Full attachment of 2kDa PEG, with an approximately 2nm gyration radius, decreases the velocity and fraction of moving actin filaments by approximately 10% relative to unattached filaments. For the 5kDa PEG, the fraction of moving filaments is decreased by approximately 70% even when the filaments contain only 20% PEG-attached actin. The attachment of both sizes of PEGs suppresses the actin-activated ATPase activity at the same level. These results suggest that actin filaments can carry PEGs up to 2kDa having the same size as actin monomers, while the rate of ATP hydrolysis is limited. The size dependence may provide a criterion for material delivery via actin filaments in nanotransport applications.