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The complete amino acid sequence of the Ca2+-dependent modulator protein (calmodulin) of bovine brain
Abstract:
We present the data required to establish the complete amino acid sequence of bovine brain modulator protein, the multifunctional calcium-dependent regulatory protein. Bovine brain modulator protein contains 148 amino acid residues and has a molecular mass of 16,680 daltons. The protein commences with an acetylated alanyl residue in accord with the previous report that its NH2 terminus was blocked. The single residues of histidine and trimethyllysine occur at positions 107 and 115, respectively, in a region of the linear sequence implicated by other studies as important for calcium-dependent modulator protein-enzyme interactions. The sequence of bovine brain modulator protein demonstrated here is closely related to those of muscle troponin Cs, as originally suggested from considerations of the similarities in calcium binding and functional and physicochemical properties of these proteins (Watterson, D.M., Harrelson, W.G., Jr., Keller, P.M., Sharief, F., and Vanaman, T.C. (1976) J. Biol. chem. 251, 4501-4513). The linear amino acid sequence of bovine brain modulator protein is composed of four internally homologous sequences or domains, each of which contains the appropriate amino acids arranged so as to form a helix-loop-helix, calcium-binding structure. The high level of internal homology of bovine brain modulator protein and its relationship to the other members of the calcium-binding protein superfamily provide convincing evidence that 1) it arose early in the evolution of these related proteins and 2) it was formed by two successive tandem duplications of a gene encoding a small, single domain ancestral precursor. Comparison with the nearly complete sequences of the bovine uterus and rat testis modulator proteins reported by other laboratories indicates that this ubiquitous calcium-dependent regulatory protein does not occur in tissue-specific forms, commensurate with the proposed function of modulator protein as a mediator of calcium-second messenger function in eukaryotic cells.
Insights
We determined the complete amino acid sequence of bovine brain modulator protein, a key calcium-dependent regulatory protein. This ubiquitous protein, crucial for calcium signaling, shows evolutionary links to other calcium-binding proteins.
Area of Science:
- Biochemistry
- Molecular Biology
- Evolutionary Biology
Background:
- Bovine brain modulator protein is a multifunctional calcium-dependent regulatory protein.
- Its structure and function are crucial for understanding calcium signaling pathways in eukaryotic cells.
Purpose of the Study:
- To establish the complete amino acid sequence of bovine brain modulator protein.
- To investigate its evolutionary origins and relationship to other calcium-binding proteins.
- To determine if tissue-specific forms of this protein exist.
Main Methods:
- Amino acid sequencing of bovine brain modulator protein.
- Sequence comparison with muscle troponin Cs and other modulator proteins.
- Analysis of internal homology and evolutionary duplication events.
Main Results:
- The complete amino acid sequence of bovine brain modulator protein (148 residues, 16,680 daltons) was established.
- The protein has an acetylated N-terminus and contains histidine and trimethyllysine residues critical for enzyme interactions.
- The sequence exhibits high internal homology, comprising four helix-loop-helix calcium-binding domains.
- Bovine brain modulator protein is closely related to muscle troponin Cs and other calcium-binding proteins.
- Evidence suggests the protein evolved through gene duplication events.
- Comparison with bovine uterus and rat testis modulator proteins indicates no tissue-specific forms.
Conclusions:
- The determined amino acid sequence provides a foundation for understanding bovine brain modulator protein's function.
- The protein's structure and evolutionary history suggest an early origin within the calcium-binding protein superfamily.
- The absence of tissue-specific forms supports its proposed ubiquitous role in mediating calcium-second messenger functions.