A comparison of the amino acid sequences of rabbit skeletal muscle alpha- and beta-tropomyosins

Abstract

Elucidation of the complete amino acid sequence of rabbit skeletal beta-tropomyosin has shown that it has the same number of residues (284) per chain as the alpha component from the same source. The presence of more than one form of beta-tropomyosin was indicated by the detection of heterogeneity at 11 positions in the sequence. The ratio of the major form to the minor form(s) was estimated to be about 10:1. Of the 39 amino acid residue differences in the major alpha and beta forms, most involve chemically similar residues with only two leading to a more negative net charge on the beta form (Ser-229 to glutamic acid and His-276 to asparagine). These replacements do not significantly affect the repeating heptapeptide pattern of nonpolar and polar residues in tropomyosin nor the 14-fold periodicity of acidic and outer nonpolar residues implicated in its binding to F-actin. The larger number of substitutions in the COOH-terminal half of the protein is reflected in differences in the smoothed alpha-helix parameters of the beta-tropomyosin sequence when compared with that of the alpha component. These differences may be related to a lower binding affinity of beta-tropomyosin to troponin.