The molecular basis of cross-bridge function

8. Conclusion: Three of the four states anticipated by the Lymn-Taylor cross-bridge cycle are now known in atomic detail. The “unbound” states, which are more easily available to protein crystallographic analysis, have yielded most information. The connections between ATP binding and the conformation of the myosin cross-bridge in solution are well understood. Besides being an ATPase the myosin “head” has two essential functions: a shape change induced by product release that drives contraction; a large change of affinity for actin induced by binding ATP. X-ray crystallography, in conjunction with electron microscopy has recently yielded an explanation of both these phenomena in molecular terms. The detailed structures of the actin bound states are gradually becoming available by combining crystal structures analysis with high-resolution electron microscopy. However, the structure of the ephemeral strong binding at the beginning of the power stroke can at present only be inferred