Background and purpose: Tropomyosin (TM) is an actin-binding protein, which is localized head to tail along the length of the actin filament. There are three major TM isoforms in human striated muscle. Mutations in beta-tropomyosin (TPM2) have recently been identified as an important cause of neuromuscular disorders.
Materials and methods: The expression of TM isoforms in patients carrying mutations in TPM2 was detected using a combination of SDS-PAGE, Western blotting, and a new method to measure the relative abundance of the various TM transcripts.
Results: The level of gamma-TM is reduced in patients with mutations in TPM2. Beta-tropomyosin was expressed at high levels in muscle specimens of the patients.
Discussion: Our study indicates that beta-TM gene mutations can alter the expression of other sarcomeric TM isoforms and that the perturbation of TM isoform levels may affect the dimer preference within the thin filaments, which may contribute to muscle weakness as a result of both functional and structural changes in muscle.