Can We Study Titin Properties in Single Myofibrils?

Titin is a giant structural protein in muscle that spans the half sarcomere from the z-line to the M-band. Although much is known about titin’s mechanical properties from tests on isolated molecules or recombinant fragments, there is little information on its behaviour within the structural confines of a sarcomere. Because of its size (>3MDa) and instability, it is hard to isolate titin and test it mechanically, although rare attempts have been made [1]. Recent work demonstrated that titin accounts for most (90-95%) of the passive forces in single myofibrils [2], and that titin’s intra-sarcomeric properties may differ from those observed in the isolated molecule [3]. Therefore, the purpose of this study was to determine the intrasarcomeric properties of titin and compare those to the properties observed in isolated titin preparations.