Structure of Limulus and Other Invertebrate Thick Filaments
We have demonstrated remarkable similarity among the skeletal muscles of chelicerate arthropods with respect to the cross-bridge arrangement on the surface of their thick filaments. The latter, gently isolated from the muscles of three representative species (Limulus telson, tarantula leg and scorpion leg and tail) have been examined by electron microscopy and optical diffraction using both negatively stained and unidirectionally metal shadowed preparations. The filaments are highly periodic and produce clear and detailed diffraction patterns. The cross-bridge projections form integral surface helices, with an axial spacing of 14.5 nm between adjacent crowns and a major axial repeat every 43.5 nm. We have demonstrated previously that Limulus filaments are four-stranded and analysis of both electron micrographs and their transforms, as well as optical reconstructions of the arachnid filaments is consistent with their also having a four-start surface helix, which is right-handed in all cases. Of all those examined thus far, only Limulus thick filaments have been demonstrated to change length under various conditions. Shortened Limulus filaments isolated from K+-stimulated fibers retain the 43.5 nm axial repeat periodicity and 14.5 nm axial spacing between crowns. In preliminary analysis of negatively stained and metal shadowed preparations, we see no systematic change with respect to screw or rotational symmetry in short as compared with long filaments. A few of the former have a very slightly increased diameter (3–4 nm) in the middle of each filament arm. This region often shows disorder on optical transforms. From our results we cannot rule out the possibility that disaggregation and reaggregation of thick filament proteins accompany the changes in length of Limulus thick filaments.
KeywordsMyosin Head Layer Line Thick Filament Filament Length Optical Diffraction
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- Barnes, R.D. (1969). The Chelicerates. In: Invertebrate Zoology. 2nd Ed. Philadelphia: W.B. Saunders Co., Chapt. 13.Google Scholar
- Davidheiser, S., Levine, R.J.C. and Davies, R.E. (1982). Two different fiber types in Limulus telson muscle. Fed. Proc. 41: 1522 (abstract).Google Scholar
- Dewey, M.M., Levine, R.J.C., Colfiesh, D.E., Walcott, B., Brann, L., Baldwin, A. and Brink, P. (1979) Structural changes in thick filaments during sarcomere shortening in Limulus striated muscle. In: Cross bridge Mechanism in Muscle Contraction pp. 3–22, ed. Sugi, H. and Pollack, G.H. Tokyo: University of Tokyo Press.Google Scholar
- Kensler, R.W., Levine, R.J.C., Reedy, M. and Hofman, W. (1982). Arthropod thick filament structure. Blophys. J. 37: 34a (abstract).Google Scholar
- Levine, R.J.C., Elfvin, M., Dewey, M.M. and Walcott, B. (1976). Paramyosin in invertebrate muscles. II. Content in relation to structure and function. J. Cell Biol. 71: 273–279.Google Scholar
- Levine, R.J.C. and Kensler, R.W. (1982) Platinum shadowing of Limules thick filaments. Biophys. J. 37: 50 (abstract).Google Scholar
- Levine, R.J.C., Kensler, R.W., Stewart, M. and Haselgrove, J. (1982). Molecular organizaton of Limules thick filaments. In: Basic Biology of Muscles: A Comparative Approach pp. 37–51, ed. Twarog, B.M., Levine, R.J.C. and Dewey, M.M. New York: Raven Press.Google Scholar
- Vibert, P.J. and Craig, R. (1982). Three-dimensional reconstruction of scallop thick filaments. Biophys. J. 37: 266 (abstract).Google Scholar
- Wray, J.S. (1982). Organization of myosin in invertebrate thick filaments. In: Basic Biology of Muscles: A Comparative Approach. Ed. Twarog, B.M., Levine, R.J.C. and Dewey, M.M. New York: Raven Press.Google Scholar
- Wray, J.S., Vibert, P.J. and Cohen, C. (1974). Cross-bridge arrangements in Limulus muscle. J. Mol. Biol. 88: 343–348.Google Scholar