3-DIMENSIONAL ATOMIC MODEL OF F-ACTIN DECORATED WITH DICTYOSTELIUM MYOSIN-S1

ELUCIDATION of the molecular contacts between actin and myosin is central to understanding the force-generating process in muscle and other cells. Actin, a highly conserved globular protein found in all eukaryotes, polymerizes into filaments (F-actin) for most of its biological functions. Myosins, which are more diverse in sequence, share a conserved globular head of about 900 amino acids in length (subfragment-1 or S1) at the N-terminal end of the molecule. S1 contains all the elements necessary for mechanochemical force transduction in vitro1,2. Here we report an atomic model for the actomyosin complex produced by combining the atomic X-ray structure of F-actin3,4 and chicken myosin S1(5) with a three-dimensional reconstruction from electron micrographs of frozen-hydrated F-actin decorated with recombinant Dictyostelium myosin S1. The accuracy of the reconstruction shows the position of actin and myosin molecules unambiguously.