Divalent cation induced actin ring formation

In this paper we explored the effect of copper sulphate on the morphology of actin filaments. Actin filaments attain different shapes and structure when exposed to 2 mM concentration of copper sulphate. Lateral branches were observed after 4 h of incubation while shapes like Y- and V- were formed after 8 h of incubation. Rings and loops of actin filaments were formed when the concentration of copper sulphate was increased from 2 to 5 mM. Additionally, ring formation was also observed when bead tailed actin filaments were incubated with copper sulphate (5 mM). Electrostatic adhesion energy between ends of actin filaments attracted due to counterion was estimated to be 7.34 kT/μm. Divalent cation induced actin ring formation are similar to toroids of DNA but actin filaments have great bending stiffness due to large diameter of the ring formed. From these results we proposed that polyelectrolyte nature of actin filaments leads to the change in their morphology on exposure to high concentration divalent cations.