A-Tropomyosin

ATP -I- tropomyosin <1> (<1> the phosphorylation site is a single serine-residue close to COOH-terminus, i.e Ser-283 [2] <1> a-tropomyosin subunit preferred over -tropomyosin subunit [1,2] <1> other poor substrates are )3-tropomyosin from chicken leg muscle, rabbit skeletal muscle... 

Averaged helical hydrophobic moment ratios are evaluated in order to assess the potential of amphiphilic regions contributing to the helix-helix interaction responsible for stabilization of tropomyosin dimers. These ratios yield profiles that are higher in the amino-terminal half than in the carboxyl-terminal half of a and p tropomyosin chains. The higher profiles found in the amino-terminal half of a tropomyosin may contribute to the greater stability of the dimer in this region. 

Tropomyosin is a two-stranded, o-helical coiled-coil molecule that aggregates head-to-tail with others to form long filamentous ropes. These lie in each of the two long period grooves of the actin microfilaments where, in vertebrate skeletal muscle, they play an important part in the Ca2+-mediated regulation of actin via troponin (a tropomyosin-associated protein). An important feature of tropomyosin is its 39.2-residue period— that is also quasi-halved (19.6 residues)—in the linear distribution of the acidic residues and, to a lesser extent, the apolar residues (McLachlan and Stewart, 1976 Parry, 1975). The number of residues in tropomyosin (284 residues), and the head-to-tail overlap (nine residues) that allows axial... 

Fig. 7. (A) Tropomyosin contains two right-handed o-helical chains (in blue and...

Li, Y., Mui, S., Brown, J. H., Strand, J., Reshetnikova, L., Tobacman, L. S., and Cohen, C. (2002). The crystal structure of the C-terminal fragment of striated-muscle a-tropomyosin reveals a key troponin T recognition site. Proc. Natl. Acad. Sci. 99, 7378-7383. 

One family with CCD arising from an RyRl mutation also had nemaline rods similar to those found with nemaline myopathies (NM) (Scacheri 2000). Muscle fibers from these patients show frequent clusters of rod-like structures. The autosomal dominant form of NM has been linked to mutations in the genes for a-tropomyosin and skeletal a-actin. A recessive form is associated with mutations in nebulin and a-tropomyosin. A major, unanswered question is whether and/or how a mutation in RyRl can produce a similar pathology. 

Stone, D., and Smillie, L. B. (1978). The amino acid sequence of rabbit skeletal a-tropomyosin The N-terminal half and complete sequence. J. Biol. Chem. 253, 1137-1148. 

Greenfield, N. J., Montelione, G. T., Farid, R. S., and Hitchcock-DeGregori, S. E. (1998). The structure of the N-terminus of striated muscle a-tropomyosin in a chimeric peptide Nuclear magnetic resonance structure and circular dichroism studies. 

Parry, D. A. (1981). Analysis of the amino acid sequence of a tropomyosin-binding fragment from troponin-T. / Mol. Biol. 146, 259-263. 

Sano, K.-I., Maeda, K., Oda, T., and Maeda, Y. (2000). The effect of single residue substitutions of serine-283 on the strength of head-to-tail interaction and actin binding properties of rabbit skeletal muscle a-tropomyosin. /. Biochem. 127, 1095-1102. 

Shape and dimension, (a) Tropomyosin, a 70-kd muscle protein, is a two-stranded a-helical coiled coil. Estimate the length of the molecule, (h) Suppose that a 40-residue segment of a protein folds into a two-stranded antiparallel P structure with a 4-residue hairpin turn. What is the longest dimension of this motif ... 

Smooth muscle. Smooth muscle, in contrast with skeletal muscle, is not regulated by a tropomyosin - troponin mechanism. Instead, vertebrate smooth muscle contraction is controlled by the degree of phosphorylation of its light chains. Phosphorylation induces contraction, and dephosphorylation leads to relaxation. Like that of skeletal muscle, smooth muscle contraction is triggered by an increase in the cytoplasmic calcium ion level. Propose a mechanism for this action of calcium ion on the basis of your knowledge of other signal-transduction processes. 

The amino acid sequence of the /8-tropomyosin subunit is mostly the same as that of a-tropomyosin, with the difference being 39 residues. Most residues were replaced by the same family of amino acid residues, with the exception that Ser-229 and His-276 in the a-subunit are replaced by Glu-229 and Asn-276 in the /8-subunit. Hence, /3-tropomyosin is a little more acidic than a-tropomyosin (Mak et ai, 1980). 

Filamentous tropomyosin molecules form long end-to-end filaments by ionic interaction. Thus aqueous solutions of tropomyosin are highly viscous. The viscosity of the solution is decreased by the addition of salt, and increased by the addition of troponin (Ebashi and Kodama, 1965). The C-terminal nine residues of a-tropomyosin are considered to be involved in the bond formation consequently the nine N-terminal residues would also be involved (McLachlan and Stewart, 1976a). 

Dyspnea, chest pain or syncope, usually features ventricular hypertrophy with impingement on LV volume and often LV outflow obstruction. Most cases hereditary, but some are new mutations. Defective genes for/3-MHC, either MLC, TnT, Tnl, a-tropomyosin, myosin binding protein C. 

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