Titin (aka connectin) is a megaprotein that is approximately 3 megadaltons in size. In
addition to being the largest protein found in mammalian tissues, it is also the third - most abundant. A single titin molecule is estimated to be between 2 and 2.5 μ M in length. In striated muscle, titin thus spans fully half of a sarcomere, with its C - terminal end localizing in the M - line at the center of the sarcomere and the N - terminal forming an integral part of the Z - line. Titin aids in maintaining sarcomeric
alignment of the myofi bril during contraction. Titin integrates the Z - line and the
thick fi laments, maintaining the location of the thick fi laments between the Z - lines. Titin is also hypothesized to play a role in generating at least a portion of the passive tension that is present in skeletal muscle cells. During development of the myofi bril, titin is one of the earliest proteins expressed, and it is thought to act as a “ molecular ruler ” by providing a scaffolding or template for the developing myofi bril