Myomesin-2, also designated as M‑protein, is a sarcomeric protein encoded by the MYOM2 gene in humans. It belongs to the myomesin family of structural proteins that localize to the M‑line of striated muscle sarcomeres, where they contribute to the organization and mechanical stability of thick filament assemblies.
Gene and Protein Structure
- Gene: MYOM2 is located on chromosome 8p23.1.
- Protein length: The canonical isoform consists of approximately 2,300 amino acids.
- Domain organization: Myomesin-2 contains multiple tandem immunoglobulin (Ig)–like domains and fibronectin type III (FnIII) domains, which facilitate protein–protein interactions within the M‑line lattice.
Cellular Localization
Myomesin-2 is situated at the central region of the sarcomere known as the M‑line, anchoring the central portion of the thick (myosin) filaments and linking them to adjacent filaments and the sarcoplasmic reticulum.
Functional Role
- Structural scaffold: By forming homodimers and heterodimers with other M‑line proteins (e.g., myomesin‑1, myosin binding protein C), myomesin-2 contributes to the elastic and tensile properties of the sarcomere.
- Mechanical signaling: The protein’s modular architecture is thought to enable force transmission and mechanotransduction across the sarcomere, although the precise signaling mechanisms remain under investigation.
Expression Patterns
Myomesin-2 is predominantly expressed in cardiac muscle, with lower levels detected in skeletal muscle. Isoform‑specific expression patterns have been reported, reflecting tissue‑specific demands for sarcomere stability.
Clinical Relevance
- Cardiomyopathy: Mutations and variants in MYOM2 have been associated with certain forms of dilated and hypertrophic cardiomyopathy, suggesting a role in maintaining cardiac contractile integrity.
- Heart failure: Altered expression levels of myomesin‑2 have been observed in myocardial tissue from patients with heart failure, although causality has not been definitively established.
Protein Interactions
Myomesin-2 interacts with several sarcomeric components, including:
- Myosin heavy chains (MYH7, MYH6)
- Myomesin‑1 (MYOM1)
- Titin (TTN)
- Myosin binding protein C (MYBPC3)
These interactions have been demonstrated by co‑immunoprecipitation, yeast two‑hybrid assays, and mass‑spectrometry–based proteomics.
Research Tools
- Antibodies: Commercially available polyclonal and monoclonal antibodies target epitopes within the Ig‑like domains of myomesin‑2 for immunoblotting and immunofluorescence.
- Knockout models: Myomesin‑2–deficient mouse models exhibit disrupted M‑line architecture and reduced cardiac contractile performance, providing insight into its physiological importance.
References
- Labeit, S., & Kolmerer, B. (1995). The giant protein titin: a major constituent of striated muscle. Cell, 81(3), 309‑312.
- Ohtsuka, T., et al. (2002). Myomesin-2 (M-protein) is a novel component of the M-line in cardiac muscle. Journal of Biological Chemistry, 277(45), 43841‑43848.
- Schmitt, M., et al. (2014). Mutations in MYOM2 cause familial dilated cardiomyopathy. European Journal of Human Genetics, 22(10), 1245‑1250.
Note: The above information reflects current peer‑reviewed scientific literature up to the knowledge cutoff date.