Department of Biochemistry, Memorial University, St. John's, Newfoundland A1B 3X9, Canada.
Faculty of Medicine, Dalhousie University, Halifax, Nova Scotia B3H 4R2, Canada.
Comp Biochem Physiol B Biochem Mol Biol. 2020 Jul;245:110439. doi: 10.1016/j.cbpb.2020.110439. Epub 2020 Apr 10.
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.
β原肌球蛋白（Tpm2）在鱼类物种中首次在蛋白质水平上被证明，使用电泳、质谱肽图谱和末端基团分析的组合。通过定量羧肽酶消化测定，Tpm2 占成年大西洋三文鱼慢肌总原肌球蛋白的 50%，也存在于头部和胸鳍中。它不存在于快速骨骼肌（浅色）中，快速骨骼肌是最丰富的肌肉，仅由α-快速（Tpm1）同工型组成。与哺乳动物同源物不同，在阴离子去污剂存在下，三文鱼 Tpm2 的迁移速度快于三文鱼 Tpm1。其他区别特征是半胱氨酸（每个链一个）和酪氨酸（每个链五个）的含量降低，以及独特的羧基末端区域（残基 276-284）。在慢肌中存在两种α-慢原肌球蛋白（Tpm3）同工型（旁系同源物），其蛋氨酸和组氨酸的含量不同，表明 TPM3 基因的重复。首次调查的次要骨骼肌至少含有两种原肌球蛋白 - 胸鳍中的 Tpm2（约占总含量的 50%）、颚和舌中的另一种同工型，或 Tpm1（胸鳍）或 α-1 样 Tpm（颚和舌）。颊肌根据部分（浅色或深色）以不同比例含有 Tpm1 和α1 样 Tpm。在舌中的两种原肌球蛋白中，Tpm2 与肌钙蛋白-琼脂糖的亲和力相对较弱。大西洋三文鱼主要肌节原肌球蛋白的一个特征是位于残基 20-90 之间的一对相邻甘氨酸。
