The largest protein known, consisting of a continuous chain of 27,000 amino acids. Each molecule spans a distance greater than one micrometer (from the Z discs to the M discs in the striated muscles of vertebrates). Titins act as springs, pulling the muscle fiber back into shape after it is stretched. Titins come in a variety of isoforms generated by alternative splicing (q.v.). The human titin gene (TTN) is located on the long arm of chromosome 2 and contains 80,780 base pairs. It is subdivided into 178 exons, the largest of which contains 17,106 bases. The Drosophila titin gene is located at the distal end of 3L. Drosophila titin is a component of muscle sarcomeres, but it also is localized in chromosomes. Here it presumably organizes higher-order chromosome structure and provides elasticity. See Chronology, 1995, Labeit and Kolmer.
Subjects: Genetics and Genomics — Chemistry.