Mammalian skeletal muscles are heterogeneous in nature and are capable of performing various functions. Tropomyosin (Tpm) is a major component of the thin filament in skeletal muscles and plays an important role in controlling muscle contraction and relaxation. Tpm is known to consist of multiple isoforms resulting from different encoding genes and alternative splicing, along with post-translational modifications. However, a systematic characterization of Tpm isoforms in skeletal muscles is still lacking. Therefore, we employed top-down mass spectrometry (MS) to identify and characterize Tpm isoforms present in different skeletal muscles from multiple species, including swine, rat, and human. Our study revealed that Tpm1.1 and Tpm2.2 are the two major Tpm isoforms in swine and rat skeletal muscles, whereas Tpm1.1, Tpm2.2, and Tpm3.12 are present in human skeletal muscles. Tandem MS was utilized to identify the sequences of the major Tpm isoforms. Furthermore, quantitative analysis revealed muscle-type specific differences in the abundance of un-modified and modified Tpm isoforms in rat and human skeletal muscles. This study represents the first systematic investigation of Tpm isoforms in skeletal muscles, which not only demonstrates the capabilities of top-down MS for the comprehensive characterization of skeletal myofilament proteins but also provides the basis for further studies on these Tpm isoforms in muscle-related diseases.
[1]Univ Wisconsin, Dept Chem, 1101 Univ Ave, Madison, WI 53706 USA.
[2]Univ Wisconsin, Dept Cell & Regenerat Biol, 1111 Highland Ave, Madison, WI 53705 USA.
[3]Univ Wisconsin, Human Prote Program, 1111 Highland Ave, Madison, WI 53705 USA.
[4]Fudan Univ, Inst Biomed Sci, Shanghai 200032, Peoples R China.
[5]Univ Wisconsin, Dept Med, Sch Med & Publ Hlth, 1111 Highland Ave, Madison, WI 53705 USA.
[6]Karolinska Inst, Dept Physiol & Pharmacol, Dept Clin Neurosci, Clin Neurophysiol Sect, S-17177 Stockholm, Sweden.
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