Interaction of myosin subfragment 1 with F‐actin studied by differential scanning calorimetry

The thermal unfolding of the myosin subfragment 1 (S1) and of filamentous actin (F‐actin) in their strong complex obtained in the presence of ADP was studied by differential scanning calorimetry (DSC). It is shown that in the acto‐S1 complexes S1 and F‐actin melt separately, and thermal transitions of each protein can be easily followed. Interaction of S1 with F‐actin significantly increases S1 thermal stability and also affects the thermal stability of F‐actin. Although S1 unfolds at much lower temperature than F‐actin, the molecules of S1 remain bound to F‐actin even after full denaturation. Under these conditions S1 may induce cross‐linking between actin filaments. It is concluded that DSC studies on the acto‐S1 complexes offer a new and promising approach to investigate the structural changes which occur in the myosin head and in F‐actin due to their interaction.