title: Characterization of paramyosin and thin filaments in the smooth muscle of acorn worm, a member of hemichordates.
abstract: Paramyosin is a myosin-binding protein characteristic of invertebrate animals, while troponin is a Ca2+-dependent regulator of muscle contraction. Both proteins are widely distributed in protostomes, while in deuterostomes, their distribution is limited; namely, presence of paramyosin and absence of troponin are common features in echinoderm muscles, while muscles of chordates contain troponin but lack paramyosin. In this study, we examined the muscle of a hemichordate, acorn worm, to clarify whether this animal is like echinoderms or like the other deuterostome animals. We found a 100-kDa protein in the smooth muscle of acorn worm. This protein was identified with paramyosin, since the purified protein formed paracrystals with a constant axial periodicity in the presence of divalent cations as paramyosin of other animals, showed ability to interact with myosin and shared common antigenicity with echinoderm paramyosin. On the other hand, troponin band was not detected in isolated thin filaments, and the filaments increased myosin-ATPase activity in a Ca2+-independent manner. The results indicate that troponin is lacking in thin filaments of acorn worm muscle just as in those of echinoderms. The muscle of hemichordate acorn worm is quite similar to echinoderm muscles, but different from chordate muscles.
authors: Department of Nanobiology, Graduate School of Advanced Integration Science.
authors: Hiroki
authors: H
authors: Sonobe
authors: Department of Biology, Faculty of Science, Chiba University, Yayoi-Cho, Inage-ku, Chiba 262-8522, Japan.
authors: Takashi
authors: T
authors: Obinata
authors: Research Center for Marine Biology, Tohoku University, Asamushi, Aomori, 039-3501, Japan.
authors: Takuya
authors: T
authors: Minokawa
authors: EM Application Department, JEOL Ltd, Akishima, Tokyo, 196-8558, Japan.
authors: Tomohiro
authors: T
authors: Haruta
authors: Department of Liberal Arts (Biology), Saitama Medical University, 38 Morohongo Moroyama-Machi, Iruma-Gun, Saitama, 350-0495, Japan.
authors: Yuuki
authors: Y
authors: Kawamura
authors: Department of Nanobiology, Graduate School of Advanced Integration Science.
authors: Shinryu
authors: S
authors: Wakatsuki
authors: Department of Nanobiology, Graduate School of Advanced Integration Science sato@faculty.chiba-u.jp.|Department of Biology, Faculty of Science, Chiba University, Yayoi-Cho, Inage-ku, Chiba 262-8522, Japan.
authors: Naruki
authors: N
authors: Sato
mesh_terms: D000818:Animals; D002816:Chordata, Nonvertebrate / Q000235:genetics / Q000378:metabolism; D009130:Muscle, Smooth / Q000378:metabolism*; D014335:Tropomyosin / Q000235:genetics / Q000378:metabolism
chemical_list: D014335:Tropomyosin
keywords: Balanoglossus misakiensis; hemichordate; muscle proteins; paramyosin; troponin