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.
Binding sites of calmodulin and actin on the brain spectrin, calspectin.
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S Tsukita, S Tsukita, H Ishikawa, M Kurokawa, K Morimoto, K Sobue, S Kakiuchi; Binding sites of calmodulin and actin on the brain spectrin, calspectin.. J Cell Biol 1 August 1983; 97 (2): 574–578. doi: https://doi.org/10.1083/jcb.97.2.574
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