Titin
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Titin is a protein that in humans is encoded by the TTN gene. Titin is a protein, over 1 µm in length, that functions as a molecular spring that is responsible for the passive elasticity of muscle. It comprises 244 individually folded protein domains connected by unstructured peptide sequences. These domains unfold when the protein is stretched and refold when the tension is removed.
Titin Ig domains. a) Schematic of part of a sarcomere b) Structure of Ig domains c) Topology of Ig domains.
Reconstruction of the thin (green) and thick filament from mammalian cardiac tissue. Myosin is in blue, MyBP-C is in yellow, and titin is in two shades of red (dark red for titin-alpha and light red for titin-beta).
The myosin-binding protein C, cardiac-type is a protein that in humans is encoded by the MYBPC3 gene. This isoform is expressed exclusively in heart muscle during human and mouse development, and is distinct from those expressed in slow skeletal muscle (MYBPC1) and fast skeletal muscle (MYBPC2).
cMyBP-C binds the thick filament and stabilized the myosin heads in their OFF state. PDB: 8Q6T
cMYBP-C C-terminal domain (CTD) anchors to the thick filament creating bridges (C-links) towards the thin filaments. Structural data adapted from Tamborrini et al. 2023 (Nature)