Binding of tropomyosin-troponin to actin increases filament bending stiffness

Rheologic measurements show that the association of tropomyosin-troponin wi th actin filaments is responsible for the reduction of the internal chain d ynamic and increase in the mechanical rigidity of actin filaments. Basing c alculations on the linear relation between the plateau modulus, G(N)', and bending modulus, kappa, I find that tropomyosin-troponin at r(AT) = 7 incre ases actin filament stiffness by similar to 50%. This is confirmed by dynam ic light scattering. Further increases are observed at rising F-actin and c onstant tropomyosin-troponin concentrations. Tropomyosin-troponin also dela ys actin assembly and subsequent: network formation and increases filament stiffness over time. (C) 2000 Academic Press.