Demonstration of beta-tropomyosin (Tpm2) and duplication of the alpha-slow tropomyosin gene (TPM3) in Atlantic salmon Salmo salar

• Published in: Comparative Biochemistry and Physiology Part B: Biochemistry and Molecular Biology Vol. 245; p. 110439
• Main Authors: Silva, A. Madhushika M., Kennedy, Luke S., Hasan, Stephanie C., Cohen, Alejandro M., Heeley, David H.
• Format: Journal Article
• Language: English
• Published: England Elsevier Inc 01.07.2020
• Subjects: Amino Acid Sequence - genetics; Animal Fins - metabolism; Animals; Atlantic salmon; Beta tropomyosin; Cheek; Electrophoresis, Gel, Two-Dimensional; Gene duplication; Genes, Duplicate; Isoform distribution; Jaw - metabolism; Mass Spectrometry; Muscle, Skeletal - metabolism; Phylogeny; Protein Isoforms - genetics; Salmo salar - genetics; Salmo salar - metabolism; Sequence Alignment; Tongue - metabolism; Tropomyosin - chemistry; Tropomyosin - genetics; Tropomyosin - metabolism; Troponin affinity; Atlantic salmon; Gene duplication; Beta tropomyosin; Troponin affinity; Isoform distribution
• DOI: 10.1016/j.cbpb.2020.110439
• ISSN: 1096-4959

Beta tropomyosin (Tpm2) is demonstrated for the first time at the protein level in a fish species, using a combination of electrophoresis, mass spectrometric peptide mapping and end-group analysis. Tpm2 accounts for 50% of the total tropomyosin in slow trunk muscle of the adult Atlantic salmon as determined by quantitative carboxypeptidase digestion and is also present in the head and pectoral fin. It is absent in the fast skeletal (lighter-toned) trunk muscle, the most abundant muscle, which is composed solely of an alpha-fast (Tpm1) isoform. In contrast to the mammalian homologues, salmon Tpm2 migrates faster than salmon Tpm1 in the presence of anionic detergent. Other distinguishing characteristics are a reduced content of cysteine (one per chain) and tyrosine (five per chain) and a unique carboxyl-terminal region (residues 276–284). Two isoforms (paralogs) of alpha-slow tropomyosin (Tpm3) having different contents of methionine and histidine exist in slow trunk muscle indicating duplication of the TPM3 gene. Minor skeletal muscles, surveyed for the first time, contain a mix of at least two tropomyosins - Tpm2 (~ 50% of total) in pectoral fin, jaw and tongue and another isoform, either Tpm1 (pectoral fin) or alpha-1-like Tpm (jaw and tongue). Cheek muscle contains Tpm1 and alpha 1-like Tpm in varying proportion depending upon the section (light or dark). Of the two tropomyosins in tongue, Tpm2 displays comparatively weaker affinity for troponin-Sepharose. A feature of the major sarcomeric tropomyosins in Atlantic salmon is a pair of neighbouring glycines situated between residues 20–90. •Beta (Tpm2) tropomyosin is demonstrated at the protein level for the first time in a fish species.•Salmon Tpm2 has a reduced thiol and aromatic content and a unique C-terminal sequence (res 276–284) vs. mammal and bird.•Beta (Tpm2) and alpha (Tpm1) share 32 substitutions. These reverse the typical isoform-mobility relationship.•Beta (Tpm2) displays comparatively weakened affinity for troponin.•The TPM3 gene is duplicated in Atlantic salmon.and•Salmon tropomyosins possess closely situated pairs of glycines between residues 20–90 as a cold adaptive strategy.