GLOSSARY

Titin is the largest known protein in the human body; like a molecular spring, it extends from the Z line to the M line of the sarcomere and holds the thick myosin filament in the centre of the sarcomere.

Characteristics

• Size: about 3–4 million daltons and over one micrometre long; its gene has more than 300 exons.
• Elastic segment: in the I band region, titin has an extensible segment called the PEVK region, which unfolds when stretched.

Functions