Abstract
Myosin is the major protein in skeletal muscles including those of fish and shellfish. The characteristics of this protein are closely related to the biological function and the quality and physical properties of muscle<br />food. In the myosin rod (the coiled-coil region of myosin), several amino acid residues, known as skip residues, seem to destabilize the ordered structure (heptad repeat). These residues might be responsible for reducing thermal stability. Attempts were thus made to examine the role of these residues in the rod of squid myosin, based on the thermodynamic properties of synthetic peptides which have been designed to mimic the partial sequence of myosin heavy chain from the squid Todarodes pacificus mantle muscle. Five peptides, namely, with the sequence of Trp1343 -Ala1372 having the skip residue Glu1357 at the center (Peptide WT), without the skip residue (Peptide Δ), with the replacements of the skip residue (Glu) by Ile, Gln and Pro (Peptides E/I, E/Q, and E/P, respectively) to modify the helix forming propensity, were synthesized. The results obtained showed that the stability of the peptides as measured by circular dichroism spectrometry was in the order of Peptide Δ &gt; Peptide WT &gt; Peptide E/Q &gt; Peptide E/P &gt; Peptide E/I. It is suggested that the presence of the skip residues dexterously tunes the stability or flexibility of the coiled-coil structure, thus possibly regulating thick filament formation and further gel formation ability of myosin.
Highlights
Myosin is the principal contractile component in muscles and makes up the major protein in the myofibril (Harrington and Rogers 1984)
Force is generated by the interaction of myosin heads with actin filament, force transduction requires the assembly of myosin molecules
The Rf values of the peptide bands on the gel did not correspond well to the molecular weight calculated from the amino acid sequences (Figure 2): i.e., the expected molecular weights from amino acid sequence were 3,471 for Peptide WT, 3,342 for Peptide Δ, 3,456 for Peptide E/I, 3,471 for Peptide E/Q, and 3,440 for Peptide E/P
Summary
Myosin is the principal contractile component in muscles and makes up the major protein in the myofibril (Harrington and Rogers 1984). The structural and functional properties of fish and shellfish myosins have been intensively studied, because of their importance in muscle contraction under various habitat conditions and in their gel forming ability. In skeletal muscles including from fish and shellfish, myosin assembles into stable thick filaments. Muscle myosins and those found in other tissues belonging to the Class II, called as conventional myosins, resemble each other both structurally and functionally. The myosins belonging to Class II are able to form thick filaments via the side-by-side association of the long coiled-coil rods. The conventional myosin molecule is a hexameric protein composed of a pair of heavy chains (approximately 200 kDa) and two pairs of light chains (approximately 20 kDa). The rod portion itself is responsible for the assembly of myosin molecules into filaments
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