INTERACTION OF ALPHA-ACTININ AND NEBULIN INVITRO - SUPPORT FOR THE EXISTENCE OF A 4TH FILAMENT SYSTEM IN SKELETAL-MUSCLE

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 α-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 α-actinin, Nebulin is the only polypeptide decorated by α-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. © 1990.