Protein osmotic pressure modulates actin filament length distribution

Abstract

1. The changes of the macromolecular osmotic pressure associated with F-actin solutions are related to the changes of the free energy of the free actin monomers. 2. By making use of the model of Biron et al. [2006. Inter-filament attractions narrow the length distribution of actin filaments. Europhys. Lett. 73, 464–470], the changes of the free energy of the free actin monomers are related to the changes of the length distribution of the actin filaments. On these bases, we propose that the length distribution of the actin filaments is regulated by (a) the free energy of hydrolysis of ATP and (b) the macromolecular osmotic pressure. a. While the free energy of hydrolysis of ATP tends to zero, the length distribution of the actin filaments shifts from an exponential curve to a straight line parallel to the abscissa axis (i.e. the concentration of the actin filaments becomes independent of their length). In the mean time, the total energy of the actin filaments reaches a minimum. b. With the increase of the macromolecular osmotic pressure the free energy of the actin monomers increases and a break is introduced in the curve that describes the length distribution of the actin filaments; the break is located at the mean length of the filaments.