Complexes between 15 kDa caldesmon fragment and actin investigated by immuno-electron microscopy.
The regulatory system of smooth muscle thin filaments is thought to involve a major calcium-calmodulin and actin binding protein: caldesmon. A dissective approach was used to isolate a 35 kDa C-terminal fragment of the molecule and to produce antibodies reacting against both the intact and the 15 kDa N-terminal end of this parental fragment. While this purified 15 kDa caldesmon fragment demonstrates a weak actin association, we observed that it cross-links actin filaments into loose bundles. These structures were labelled with a selective antibody and showed regular periodic striation with repeats of approximately 40 nm. This work brings additional information to previous reports using an actin and calmodulin binding 25 kDa C-terminal fragment of the caldesmon molecule [(1989) J. Biol. Chem. 264, 2869-2875]. We demonstrate that a purified fragment corresponding to a sequence smaller than 96 amino acids, which contains no cystein residue, is able to interact with actin at a single site which is not the calmodulin modulated.
Harricane
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MC
Centre de Biochimie Macromoléculaire du CNRS, INSERM U.249, Université de Montpellier, France.
Cavadore
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C
Audemard
E
E
Mornet
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D
D000199:Actins / Q000378:metabolism* / Q000648:ultrastructure; D000818:Animals; D015153:Blotting, Western; D002148:Calmodulin-Binding Proteins / Q000378:metabolism* / Q000648:ultrastructure; D066298:In Vitro Techniques; D046911:Macromolecular Substances; D008840:Microfilament Proteins / Q000378:metabolism* / Q000648:ultrastructure; D008854:Microscopy, Electron; D010446:Peptide Fragments; D011485:Protein Binding; D014422:Turkeys
D000199:Actins; D002148:Calmodulin-Binding Proteins; D046911:Macromolecular Substances; D008840:Microfilament Proteins; D010446:Peptide Fragments