Nebulin's an actin-binding protein which's localized to the I-band of the sarcomeres in skeletal muscle. It's a very large protein (600-900 kDa) and binds as many as 200 actin monomers. Because its length's proportional to thin filament length, it's believed that nebulin acts as a thin filament "ruler" and regulates thin filament length during sarcomere assembly. Other functions of nebulin, such as a role in cell signaling, remain uncertain. The interaction of nebulin with actin's calcium-calmo… (More on Nebulin)