Understanding the functions of titin and nebulin.

Individual molecules of the giant muscle proteins titin and nebulin span large distances in the sarcomere. Approximately one-third of the titin molecule forms elastic filaments linking the ends of thick filaments to the Z-line. The remainder of the molecule is probably bound to the thick filament where it may regulate assembly of myosin and the other thick filament proteins. This region also contains a sequence similar to catalytic domains in protein kinases. Nebulin appears to be associated with thin filaments and may regulate actin assembly.