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

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Abstract
Titin is a term used to describe a pair of closely related megadalton polypeptides that together are the 3rd most abundant myofibrillar protein in a wide range of [rabbit] striated muscles. It has been preposed that titin and another giant protein, nebulin, are the major components of an elastic cytoskeletal lattice within the sarcomere. The leading band, titin-2 (T2), of the titin doublet in native forms was purified by extraction with Guba-Straub solution followed by chromatography. EM of low-angle-shadowed and negatively stained specimens revealed that T2 chains self-assembled into extremely long (from 0.1 .mu.m to > 1.0 .mu.m), flexible and extensible slender strands (4-5 nm in diameter) with axial periodicity. These strands tended to associate to form filamentous bundles and meshworks. 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.