Conformational transitions in the subfragment-2 region of myosin.

A differential scanning calorimeter was used to observe thermally induced conformational transitions in subfragment 2 (S-2) of myosin. In addition to an endotherm for the major transition which had been observed by several other methods earlier, a small broad endotherm was noted with a Tm of 41 degrees C. By analysis of the heat capacity profiles of long and short S-2, this endotherm was assigned to the hinge region. Comparison of the amino acid compositions of S-2 and tropomyosin showed them to be remarkably similar, and in view of their similar behavior in calorimetric studies, it is apparent that interactions stabilizing the coiled-coil structure of S-2 are a hydrophobic interface supported by charged interaction spanning the groove as was suggested for tropomyosin by McLachlan and Stewart [McLachlan, A. D., & Stewart, M. (1975) J. Mol. Biol. 98, 293-304].