ACTIN-CROSS-LINKING PROTEIN-REGULATION OF FILAMENT MOVEMENT IN MOTILITY ASSAYS - A THEORETICAL-MODEL

The interaction of single actin filaments on a myosin-coated coverslip has been modeled by several authors. One model adds a component of '' frictional drag'' by myosin heads that oppose movement of the actin fi laments. We have extended this concept by including the resistive drag from actin crosslinking proteins to understand better the relationshi p among crosslinking number, actin-myosin force generation, and motili ty. The validity of this model is supported by agreement with the expe rimental results from a previous study in which crosslinking proteins were added with myosin molecules under otherwise standard motility ass ay conditions. The theoretical relationship provides a means to determ ine many physical parameters that characterize the interaction between a single actin filament and a single actin-crosslinking molecule (var ious types). In particular, the force constant of a single filamin mol ecule is calculated as 1.105 pN, approximately 3 times less than a dri ving myosin head (3.4 pN). Knowledge of this parameter and others deri ved from this model allows a better understanding of the interaction b etween myosin and the actin/actin-binding protein cytoskeleton and the role of actin-binding proteins in the regulation and modulation of mo tility.