title: Binding sites of calmodulin and actin on the brain spectrin, calspectin.
abstract: We used rotary-shadowing electron microscopy to map the calmodulin-and actin-binding sites on the brain spectrin, calspectin (or fodrin). Calspectin dimers appeared as rods 110 nm long and joined in a head-to-head manner to form tetramers 220 nm long. We determined calmodulin-binding sites by a ferritin-labeling method combined with biotin-avidin complex formation. Ferritin particles were found to attach to the head parts of calspectin dimers at a position 10-20 nm from the top of the head. The number of the calmodulin-binding sites seemed to be only one for each dimer and two for each tetramer. In contrast, the actin-binding sites were localized at the tail ends of the calspectin molecules. The tetramers attached to muscle F-actin with their tail ends and often cross-linked adjacent filaments. The results are discussed in view of the analogy to the erythrocyte spectrin.
mesh_terms: D000199:Actins / Q000378:metabolism*; D000818:Animals; D001665:Binding Sites; D001921:Brain / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000378:metabolism*; D002147:Calmodulin / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism*; D002417:Cattle; D066298:In Vitro Techniques; D008840:Microfilament Proteins; D008854:Microscopy, Electron; D011487:Protein Conformation; D013049:Spectrin
chemical_list: D000199:Actins; D002135:Calcium-Binding Proteins; D002147:Calmodulin; D002352:Carrier Proteins; D008840:Microfilament Proteins; D013049:Spectrin