Determination of the Complete Amino Acid Sequence of Calmodulin (Phenylalanine-Rich Acidic Protein Ii) From Bovine Brain

The complete amino acid sequence of calmodulin (phenylalanine-rich acidic protein II) purified from bovine brain was determined. The peptides derived from the fragmentation with trypsin, cyanogen bromide, pepsin and S. aureus V8 protease were separated and sequenced. Bovine brain calmodulin consists of 148 amino acid residues with a calculated molecular weight of 16,676 daltons, containing one residue of trimethyllysine and histidine per molecule and no tryptophan residue. The N-terminus of the protein is blocked with acetyl group. The sequence demonstrated here was virtually identical with the sequence of bovine brain calmodulin recently reported by Watterson er al. ( Bovine brain calmodulin consisted of the four homologous domains like troponin C. The secondary structure predicted for calmodulin accordingrto the method of Nagano (30) supported the hypothesis that each domain could form the helix-loop-helix structure proposed by Tufty and Kretsinger (39). The predicted ,8-turns between the two adjacent domains were related with a possible role of a single residue of trimethyllysine in calmodulin. The identical sequence of Asp-Gly-Asp-Gly found in each Ca"-binding loop of the four domains of calmodulin exists commonly in parvalbumins from muscle and brain-specific S-I00 protein. In this respect, the common ancestral sequence for Ca-binding was discussed.