Tropomyosin polymerization

Miki M, Dosremedios CG (1988) Fluorescence quenching studies of fluorescein attached to Lys-61 or Cys-374 in actin effects of polymerization, myosin subfragment-1 binding, and tropomyosin-troponin binding. J Biochem Tokyo 104 232-235... 

Movement. The interaction between actin and myosin is responsible for muscle contraction and cell movement (see p.332). Myosin (right), with a length of over 150 nm, is among the largest proteins there are. Actin filaments (F-actin) arise due to the polymerization of relatively small protein subunits (G-actin). Along with other proteins, tropomyosin, which is associated with F-actin, controls contraction. 

Paulucci, A. A., Katsuyama, A. M., Sousa, A. D., and Farah, C. S. (2004). A specific C-terminal deletion in tropomyosin results in a stronger head-to-tail interaction and increased polymerization. Eur. J. Biochem. 271, 589-600. 

Sousa, A. D., and Farah, G. S. (2002). Quantitative analysis of tropomyosin linear polymerization equilibrium as a function of ionic strength. /. Biol. Chem. 277, 2081-2088. 

G-actin is soluble in water and is transformed into F-actin in neutral salt solutions. Conversion of G-actin to F-actin is associated with hydrolysis of ATP leading to the formation of filaments that are up to several micrometers long and 7 to 10 nm wide. The process has been characterized as containing two steps, that is, nucleation and growth, and as is polymerization of other macromolecules, entropy driven. In muscle actin filaments tropomyosin binds to F-actin and mechanically stabilizes them. 

All except tropomyosin form larger molecules. Tubulin, under the influence of GTP, aggregates into microtubules G-actin polymerizes to F-actin myosin forms thick filaments by tail-to-tail interaction and /3-actin polymerizes to microfilaments. /3-Actin is similar but not identical to G-actin. Tropomyosin is a fibrous protein associated with the F-actin polymer. It controls myosin-actin interaction under the influence of troponin. 

Tropomyosin shows strong affinity for troponin. Ebashi and Kodama (1965) first demonstrated that troponin greatly increased the viscosity of tropomyosin solution. Studies have indicated that troponin increases the polymerization of tropomyosin and stabilizes the polymers. 

In concentrated urea solution and at pH values below 2.8 the particle weight determined osmotically falls to 53,000, three times the minimal value from the histidine content. Since the effect of acids is fully reversible—the tropomyosin crystallizes as well afterwards as before— this is evidently the weight of the true monomer. The particle weight at 7 = 0.27 and pH 6.5 thus corresponds to an average degree of polymerization of about 2. 

Thin filaments (8 nm diam.) consist of polymerized Actin (see) (30(M00 actin molecules per 1.0 pm length), each chain being accompanied by threadlike tropomyosin molecules and, in striated muscle, globular molecules of troponin. In smooth muscle troponin is replaced by caldesmon. The actin and myosin are responsible for muscle contraction, while the tropomyosin and troponin or caldesmon are regulatory proteins... 

Tropomyosin a protein associated with Actin (see), both in muscle (see Muscle proteins) and in the cytoskeleton of other cell types There are two very similar forms in striated muscle, a-T. and P-T. Both have 284 amino acid residues (M, 33,000) per subunit. The molecule is a two-chain coiled-coil a-he-lix with the two subunits twined around one another, a-a, a-P and dimers have been observed different proportions of the two types appear in different types of muscle and may reflect specialization. T. dimers polymerize head-to-tail to form a fiber which... 

The ability to predict a band intensity profile opens up an important additional dimension in vibrational analysis. It means that we will be able to relate subtle spectral differences to small structural changes with a greater degree of confidence. Thus, it has been possible to confirm that an observed three-component contour of the amide I band of tropomyosin is indeed expected for a coiled-coil a-helix [142]. Extensions to understanding the normal modes of proteins become possible [143]. The systematic incorporation in an SDFF of dipoles and dipole fluxes to calculate IR intensities [144] will finally bring to the vibrational analysis of polymeric molecules the completeness and flexibility needed to make it a much more powerful structural tool. 

Tropomyosin forms very viscous solutions of polymeric particles. The protein can be obtained crystalline and has a molecular weight of 50,000 to 150,000 (depending on the animal species). The molecule is very asymmetric. It is a component of the myofibrils, particularly of smooth musculature. 

Tropomyosin is a long rodlike molecule that can form filaments by association in a head-to-tail fashion. A single phosphorylation site is located at the penultimate serine residue. For both polymerized and depolymerized (addition of 1 MKO) tropomyosin, a narrow resonance has bwn observed in the spectra that shifted with pH, as would be expected for an exposed phosphoserine moiety (Vogel and Biidger, 1983a). The observation of a narrow resonance for the polymerized tropomyosin, was especially unexpected because the solutions are extremely viscous. However, the tyrosine residues are also known to be mobile in the polymerized state (Edwards and Sykes, 1978). This observation raises questions about the postulated involvement of the phosphoserine in a salt linkage in the head-to-tail overlap region, as had been proposed (Mak et ai, 1978). However, further P-NMR analysis of the pH titration behavior (by means of the Hill coefiicients)... 

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