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Similarities between the Mr 245,000 calmodulin-binding protein of the dogfish erythrocyte cytoskeleton and
Abstract:
The Mr 245,000 calmodulin-binding protein of the dogfish erythrocyte cytoskeleton (D245) has been compared with human erythrocyte spectrin and mammalian brain fodrin [J. Levine and M. Willard (1981) J. Cell Biol. 90, 631-643]. Mammalian erythrocyte alpha-spectrin, brain alpha-fodrin, and D245 are all localized in the cell surface-associated cytoskeleton, and have similar molecular weights. Like mammalian erythrocyte spectrin, D245 was extracted from erythrocyte ghosts under low-ionic-strength conditions. However, D245 failed to bind an antibody which reacted strongly with both subunits of human erythrocyte spectrin. Unlike mammalian erythrocyte alpha- and beta-spectrin, D245 bound calmodulin in the absence of urea both in a "gel-binding" assay and in situ using azidocalmodulin [D.C. Bartelt, R.K. Carlin, G.A. Scheele, and W.D. Cohen (1982) J. Cell Biol. 95, 278-284]. Striking similarities were noted between D245 and alpha-fodrin in that both exhibited (a) comparable calcium-dependent calmodulin binding properties, (b) strong reactivity with two different anti-fodrin antibody preparations, (c) similar reactivity with antibody to brain CBP-I, now believed to be fodrin, (d) proteolytic degradation yielding an Mr 150,000 calmodulin-binding fragment, and (e) lack of reactivity with an anti-spectrin antibody. A protein with calmodulin-binding and anti-fodrin-binding properties similar to D245 was detected in cytoskeletal preparations of chicken erythrocytes. Moderate and consistent cross-reactivity of anti-fodrin with human erythrocyte alpha-spectrin was also observed. The data indicate that D245 is functionally and immunologically more closely related to alpha-fodrin than to alpha-spectrin of the mammalian erythrocyte.
Insights
Dogfish erythrocyte calmodulin-binding protein (D245) shares more similarities with alpha-fodrin than alpha-spectrin. This finding highlights evolutionary relationships between cytoskeletal proteins in different species.
Area of Science:
- Cell Biology
- Protein Biochemistry
- Evolutionary Biology
Background:
- The calmodulin-binding protein of the dogfish erythrocyte cytoskeleton (D245) has a molecular weight of 245,000.
- Mammalian erythrocyte spectrin and brain fodrin are key cytoskeletal proteins with established roles.
Purpose of the Study:
- To compare the dogfish erythrocyte calmodulin-binding protein (D245) with human erythrocyte spectrin and mammalian brain fodrin.
- To determine the functional and immunological relationship of D245 to spectrin and fodrin.
Main Methods:
- Extraction of D245 from erythrocyte ghosts under low-ionic-strength conditions.
- Gel-binding assays and in situ studies using azidocalmodulin to assess calmodulin binding.
- Immunological assays using antibodies against spectrin and fodrin.
Main Results:
- D245 exhibited calcium-dependent calmodulin binding properties, similar to alpha-fodrin.
- D245 showed strong reactivity with anti-fodrin antibodies but not anti-spectrin antibodies.
- Proteolytic degradation of D245 yielded a calmodulin-binding fragment of Mr 150,000, characteristic of fodrin.
Conclusions:
- Dogfish erythrocyte D245 is functionally and immunologically more closely related to alpha-fodrin than to mammalian erythrocyte alpha-spectrin.
- Similar proteins were detected in chicken erythrocytes, suggesting conserved cytoskeletal structures.
- The findings provide insights into the evolution and diversity of cytoskeletal proteins.