Nebulin (NEB)

Nebulin is an actin-binding protein which is localized to the I-band of the sarcomeres in skeletal muscle. It is a very large protein (600-900 kDa) and binds as many as 200 actin monomers. Because its length is proportional to thin filament length, it is 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.

Nebulin has also been shown to regulate actin-myosin interactions by inhibiting ATPase activity in a calcium-calmodulin sensitive manner. Mutations in nebulin cause some cases of the autosomal recessive disorder nemaline myopathy.A second smaller isoform of nebulin, termed nebulette, is expressed in cardiac muscle.