Titin is an extraordinarily long, flexible, and slender myofibrillar protein

Abstract

" Titin " is a term used to describe a pair of closely related megadalton polypeptides that together are the third most abundant myofibrillar protein in a wide range of striated muscles. It has been proposed that titin and another giant protein, nebulin , are the major components of an elastic cytoskeletal lattice within the sarcomere. We have now purified the leading band, titin -2 (T2), of the titin doublet in native forms by extraction with Guba -Straub solution followed by chromatography. Electron microscopy of low-angle-shadowed and negatively stained specimens revealed that T2 chains self-assembled into extremely long (from 0.1 micron to over 1.0 micron), flexible, and extensible slender strands (4-5 nm in diameter) with axial periodicity. Furthermore, these strands tended to associate to form filamentous bundles and meshworks. Thus, titin appears to be ideally suited as a component of an elastic lattice that serves as an organizing scaffold or template for thick and thin filaments.