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

Evaluation of the secondary structure of caldesmon from c.d. spectra r evealed that it contains 51% helix, 9% beta-strand and 40% of remainde r structures. These values agree well with the predicted ones from ami no 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, 1 3 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 analys is and fragmentation by proteolytic and chemical cleavages the six-dom ain model of caldesmon is proposed.