The effects of Ca2+ and Cd2+ on the secondary and tertiary structure of bovine testis calmodulin. A circular-dichroism study.
Near-u.v. and far-u.v. c.d. spectra of bovine testis calmodulin and its tryptic fragments (TR1C, N-terminal half, residues 1-77, and TR2C, C-terminal half, residues 78-148) were recorded in metal-ion-free buffer and in the presence of saturating concentrations of Ca2+ or Cd2+ under a range of different solvent conditions. The results show the following: if there is any interaction between the N-terminal and C-terminal halves of calmodulin, it has not apparent effect on the secondary or tertiary structure of either half; the conformational changes induced by Ca2+ or Cd2+ are substantially greater in TR2C than they are in TR1C; the presence of Ca2+ or Cd2+ confers considerable stability with respect to urea-induced denaturation, both for the whole molecule and for either of the tryptic fragments; a thermally induced transition occurs in whole calmodulin at temperatures substantially below the temperature of major thermal unfolding, both in the presence and in the absence of added metal ion; the effects of Cd2+ are identical with those of Ca2+ under all conditions studied.
D000818:Animals; D002104:Cadmium / Q000494:pharmacology*; D002118:Calcium / Q000494:pharmacology*; D002147:Calmodulin; D002417:Cattle; D002942:Circular Dichroism; D008297:Male; D010446:Peptide Fragments / Q000032:analysis; D011487:Protein Conformation / Q000187:drug effects; D013696:Temperature; D013737:Testis / Q000032:analysis*
D002147:Calmodulin; D010446:Peptide Fragments; D002104:Cadmium; D002118:Calcium