Structure of rabbit skeletal myosin: Analysis of the amino acid sequences of two fragments from the rod region

The amino acid sequences of fragments from light meromyosin and heavy meromyosin subfragment-2 have been analysed and structural features noted. As with other α-fibrous protein sequences, there is a regular disposition of apolar residues in positions a and d of the heptapeptide-type repeat characteristic of the coiled-coil conformation. The common occurrence of acidic and basic residues in the e and g positions, respectively, give rise to a maximum number of interchain ionic interactions when the two parallel chains of myosin are in axial register. Although the quasi-repeating heptapeptides in the sequences both have two points of discontinuity (unlike that in most other α-fibrous proteins), secondary structure prediction methods indicate that the fragments will be 90 to 100% α-helical. Fast Fourier transform techniques have revealed a significant periodicity of about 27.4 ± 0.3 residues (~41 Å) in the linear disposition of the acidic residues and the basic residues in both of the fragments. This period is compatible with similarly directed myosin molecules in the thick filament being axially staggered with respect to one another by an odd multiple of 143 Å. Preliminary evidence is also presented to show that the sequence of the rod region of myosin may have a 28 residue gene duplication repeat.