title: Characterization of two tropomyosin isoforms from the fast skeletal muscle of bluefin tuna Thunnus thynnusorientalis.
abstract: Fast skeletal muscle tropomyosin (TM) of tunas is composed of nearly equimolar amount of two isoforms designated alpha-TM and beta-TM expediently based on their migration behavior in SDS-PAGE, whereas corresponding TMs from the other fish species are homogenous (alpha-type). The presence of beta-TM is thus specific to tunas so far. The amino acid sequence of beta-TM from bluefin tuna Thunnus thynnus orientalis, which has not been revealed to date unlike alpha-TM, was successfully obtained in this study by cDNA cloning. The coding region of beta-TM cDNA comprised of an open reading frame of 855bp encoding 284 amino acid residues, like most of the TMs. Unexpectedly, the sequence of beta-TM showed high similarity to those of other vertebrate alpha-type TMs including tuna alpha-TM. Phylogenetic analysis also showed that beta-TM has the closest relationship with alpha-TM of tuna. This fact was quite unlike the relation of mammalian alpha- and beta-TMs. Based on the distribution of amino acid substitutions, it was suggested that tuna TM isoforms are the products of different genes. By thermodynamic analysis of native and reconstituted TMs, it was demonstrated that beta-TM is less thermostable than alpha-TM. Proteolytic digestion also supported the lower stability of the former.
authors.affiliation: Department of Aquatic Bioscience, The University of Tokyo, Bunkyo, Japan. aochiai@mail.ecc.u-tokyo.ac.jp
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Ochiai
authors.forename: Hideo
authors.initials: H
authors.lastname: Ozawa
authors.forename: Ming-Chih
authors.initials: MC
authors.lastname: Huang
authors.forename: Shugo
authors.initials: S
authors.lastname: Watabe
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D018076:DNA, Complementary / Q000235:genetics / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D005399:Fishes / Q000235:genetics / Q000378:metabolism; D018482:Muscle, Skeletal / Q000378:metabolism*; D010473:Perciformes / Q000235:genetics / Q000378:metabolism; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D014335:Tropomyosin / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D014413:Tuna / Q000235:genetics / Q000378:metabolism
chemical_list: D018076:DNA, Complementary; D020033:Protein Isoforms; D014335:Tropomyosin