STUDIES ON SECONDARY STRUCTURE OF CALDESMON AND ITS C-TERMINAL FRAGMENTS

Evaluation of the secondary structure of caldesmon from c.d. spectra revealed that it contains 51% helix, 9% beta-strand and 40% of remainder structures. These values agree well with the predicted ones from amino acid sequence, assuming an extended chain structure for caldesmon. The estimates of the secondary-structure elements in C-terminal 34 kDa and 19 kDa fragments are: 11 and 12% helix, 22 and 20% beta-strand, 13 and 17% beta-turns and loops, and 54 and 50% of remainder structure respectively. The best fit of experimental data was obtained assuming the globular state of the fragments. On the basis of structural analysis and fragmentation by proteolytic and chemical cleavages the six-domain model of caldesmon is proposed.