Slow Modulated Fluctuations in an Actin Filament as Revealed by Correlation Analysis

Matsui, M., Hatori, K.

Department of Bio-System Engineering, Yamagata University


The sliding movement of an actin filament for myosin II results from a combination among forces generated by individual myosin molecules. The fluctuated movement is likely to reflect a manner coordinating between confliction and restoration occurring everywhere in the filament. Previous research for motility had been carried out under the condition in which actin filaments slid on myosin molecules fixed on a glass surface.
In the present study myosin molecules were applied to an actin filament that was restricted on the surface by aid of biotin-avidin bonds. The advantage in the latter condition is that the fluctuations could be distinguished from the sliding motion.
In order to trace the motion of a certain part within a filament, we employed speckled actin filaments, which were prepared with mixture both rhodamine-phalloidin labeled segments and non-labeled segments. The displacements and the fluorescent intensities in the labeled segments were measured at every interval of 1/30 sec. The auto-correlation function of fluctuations in displacement revealed that relaxation time of correlation increased as ATP concentration was raised up to 100 uM. The cross-correlation function between the maximum of fluorescent intensity and the extent of its distribution also revealed the increase of negative correlation over the range of 50-200 uM of ATP, indicating the development of local distortions within the filament. In conclusion, slow modulated fluctuations of the actin filament appeared around 100 uM of ATP concentration as the features inherent in the filamental structure.