Implication of arrangement of active components along an actin filament for coordinating the sliding movement

Matsushita, S., Hatori, K.

Department of Bio-System Engineering, Yamagata University


We prepared the inactive actin molecules, of which filaments exhibit no sliding movement on myosin molecules, by conjugating fluorescent dyes to them above the molar ratio of 3. Two kinds of fluorescent dyes we used were IC3-OSu and Atto530-NHS, which could bind to primary amino groups. IC3-labeled actin monomers were observed to polymerize into the filament, on the other hand, Atto530-labeled ones impaired the ability for the polymerization. Since both sliding movements of IC3- and Atto530-labeled actin filaments were completely suppressed, the labeled actin monomers would play as inactive components. Subsequently, two types of copolymer filaments were prepared. One was the filaments copolymerized homogeneously with intact monomers and labeled monomers, and the other was block copolymers that consisted of intact short filaments and labeled ones. The sliding velocities of these different types of filaments were measured under a fluorescent microscopy at various ratio of inactive monomer (labeled one) to an entire filament. The velocity of homogeneous copolymers decreased with an increase of the ratio of inactive component. The half value of maximum velocity was attained at the ratio of approximately 70 %. The velocity of block copolymers is also found to decrease similar to fashion in the case of homogeneous copolymer. The coordinating movement may be actualized in entire filament, as being independent of the manner how parts subjected to force from myosin molecules is arranged along the filament.