Lethocerus flight muscle paramyosin: antibody localization and electrophoretic studies

Invertebrate Muscles: Muscle Specific Genes and Proteins

This is the first of a projected series of canonic reviews covering all invertebrate muscle literature prior to 2005 and covers muscle genes and proteins except those involved in excitation-contraction coupling (e.g., the ryanodine receptor) and those forming ligand- and voltage-dependent channels. Two themes are of primary importance. The first is the evolutionary antiquity of muscle proteins. Actin, myosin, and tropomyosin (at least, the presence of other muscle proteins in these organisms has not been examined) exist in muscle-like cells in Radiata, and almost all muscle proteins are present across Bilateria, implying that the first Bilaterian had a complete, or near-complete, complement of present-day muscle proteins. The second is the extraordinary diversity of protein isoforms and genetic mechanisms for producing them. This rich diversity suggests that studying invertebrate muscle proteins and genes can be usefully applied to resolve phylogenetic relationships and to understand protein assembly coevolution. Fully achieving these goals, however, will require examination of a much broader range of species than has been heretofore performed.

Differences in myosin head arrangement on relaxed thick filaments from Lethocerus and rabbit muscles

Relaxed thick filaments from insect asynchronous flight muscle appear different from those of other striated muscles, both in sections and as separated, negatively-stained structures. Unlike relaxed filaments of scallops, chelicerate arthropods, or vertebrate striated muscle, all of which display a predominantly helical arrangement of surface myosin heads, insect asynchronous flight muscle filaments appear striped, with cross-striations or shelves at spacings of 14.5 nm. Using a bifunctional agent to cross-link the active sites of nearest-neighbour myosin heads we previously demonstrated that the helical arrays on the surfaces of scallop, arthropod, fish and frog filaments are produced by the association of two oppositely-oriented myosin heads, each of which originates from an axially sequential molecule within the same helical strand. The effect of similarly cross-linking nearest-neighbour heads with the bifunctional agent 3,3'-dithiobis[3'(2')-O-(6-propionylamino)hexanoyl]adenosine 5'-triphosphate in the presence of vanadate on the solubility of thick filaments separated from Lethocerus indirect flight muscle (an insect asynchronous flight muscle) and rabbit psoas muscle was examined. After incubation on high salt, treated rabbit filaments retained their length and surface myosin, while untreated filaments and those with severed cross-links dissolved, indicating that the myosin head arrangement on rabbit filaments is similar to those previously studied. Treated indirect flight muscles filaments, however, separated into distinct segments of variable lengths, usually multiples of 150 nm, while untreated filaments and those with severed cross-links dissolved completely. This implies that intermolecular associations on indirect flight muscles filaments most likely occur between circumferentially-adjacent heads within each crown, but originating from different helical strands. We interpret this difference in the relaxed orientations of splayed myosin heads on the two types of filament as reflecting a difference in functional requirements at the onset of, or during, contractile activity.

Structure and paramyosin content of tarantula thick filaments

Muscle fibers of the tarantula femur exhibit structural and biochemical characteristics similar to those of other long-sarcomere invertebrate muscles, having long A-bands and long thick filaments. 9-12 thin filaments surround each thick filament. Tarantula muscle has a paramyosin:myosin heavy chain molecular ratio of 0.31 +/- 0.079 SD. We studied the myosin cross-bridge arrangement on the surface of tarantula thick filaments on isolated, negatively stained, and unidirectionally metal-shadowed specimens by electron microscopy and optical diffraction and filtering and found it to be similar to that previously described for the thick filaments of muscle of the closely related chelicerate arthropod, Limulus. Cross-bridges are disposed in a four-stranded right-handed helical arrangement, with 14.5-nm axial spacing between successive levels of four bridges, and a helical repeat period every 43.5 nm. The orientation of cross-bridges on the surface of tarantula filaments is also likely to be very similar to that on Limulus filaments as suggested by the similarity between filtered images of the two types of filaments and the radial distance of the centers of mass of the cross-bridges from the surfaces of both types of filaments. Tarantula filaments, however, have smaller diameters than Limulus filaments, contain less paramyosin, and display structure that probably reflects the organization of the filament backbone which is not as apparent in images of Limulus filaments. We suggest that the similarities between Limulus and tarantula thick filaments may be governed, in part, by the close evolutionary relationship of the two species.

Paramyosin in invertebrate muscles. I. Identification and localization

By sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunodiffusion, we identified paramyosin in two smooth invertebrate "catch" muscles (Mytilus anterior byssus retractor and Mercenaria opaque adductor) and five invertebrate striated muscles (Limulus telson levator, Homarus claw muscle, Balanus scutal depressor, Lethocerus air tube retractor, and Aequipecten striated adductor). We show that (a) the paramyosins in all of these muscles have the same chain weights and (b) they are immunologically similar. We stained all of these muscles with specific antibody to Limulus paramyosin using the indirect fluorescent antibody technique. Paramyosin was localized to the A bands of the glycerinated striated muscles, and diffus fluorescence was seen throughout the glycerinated fibers of the smooth catch muscles. The presence of paramyosin in Homarus claw muscle, Balanus scutal depressor, and Lethocerus air tube retractor is shown here for the first time. Of the muscles in this study, Limulus telson levator is the only one for which the antiparamyosin staining pattern has been previously reported.