This study provides biochemical evidence that alpha-actinin binds to nebulin, supporting the hypothesis that nebulin forms a fourth filament system in skeletal muscle extending to the Z-line.
No immediate clinical implications; leaves open whether nebulin-alpha-actinin binding organizes sarcomeres in vivo.
Nebulin is a high molecular weight polypeptide (mass 0.6-0.8 million) which accounts for 3% of the myofibrillar mass in skeletal muscle. Due to its resistance to extraction under native conditions, relatively little is known about the biochemistry of the molecule. Here we report in vitro binding of alpha-actinin (a major Z-line protein) to nebulin. After solubilization with sodium dodecylsulfate myofibrillar polypeptides separated by gel electrophoresis were blotted on nitrocellulose and probed with 125I-labelled alpha-actinin. Nebulin is the only polypeptide decorated by alpha-actinin. This result gives biochemical support for the hypothesis, based on recent immunoelectron micrographs, that nebulin could form in skeletal muscle a fourth filament system, possibly extending to the Z-line.
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Nave et al. (1990) studied this question.
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