The study identifies specific amino acid sequence differences between equine platelet and rabbit skeletal muscle tropomyosin that explain the diminished polymerization and weaker protein interactions of the platelet variant.
Equine platelet beta tropomyosin (247 residues), like rabbit skeletal muscle alpha tropomyosin (284 residues) has a repeating pattern of amino acid residues characteristic of a coiled-coil structure. When compared with the muscle protein, it is extended by 5 residues at the NH2-terminus and possesses two 21 residue deletions (positions 23-43 and 60-80 of the muscle sequence). The two proteins are highly conserved from residues 81-260, but are significantly different at their COOH-termini (residues 261-284). These differences in platelet tropomyosin can be correlated with its diminished head-to-tail polymerization, a weaker interaction with F-actin and a reduced affinity for muscle troponin and the T1 fragment of troponin-T.
Lewis et al. (Mon,) studied this question.