Conformational and dynamic differences between actin filaments polymerizedfrom ATP- or ADP-actin monomers

Conformational and dynamic properties of actin filaments polymerized from A TP- or ADP-actin monomers were compared by using fluorescence spectroscopic methods. The fluorescence intensity of LAEDANS attached to the Cys(374) re sidue of actin was smaller in filaments from ADP-actin than in filaments fr om ATP-actin monomers, which reflected a nucleotide-induced conformational difference in subdomain 1 of the monomer. Radial coordinate calculations re vealed that this conformational difference did not modify the distance of C ys(374) from the longitudinal filament axis. Temperature-dependent fluoresc ence resonance energy transfer measurements between donor and acceptor mole cules on Cys(374) Of neighboring actin protomers revealed that the inter-mo nomer flexibility of filaments assembled from ADP-actin monomers were subst antially greater than the one of filaments from ATP-actin monomers, Flexibi lity was reduced by phalloidin in both types of filaments.