Tropomyosin coiled-coil

Figure 19-9 Stereoscopic ribbon drawing of the proposed structure of a thin actin filament with tropomyosin coiled-coils bound on opposing sides.124 Five actin nomomers are assembled in the structure as is also illustrated in Fig. 7-10. From Lorenz et al.125 Courtesy of Michael Lorenz.

McLachlan, A. D., and Stewart, M. (1975). Tropomyosin coiled-coil interactions Evidence for an unstaggered structure. J. Mol. Biol. 98, 293-304. 

Jancso, A., and Graceffa, P. (1991). Smooth muscle tropomyosin coiled-coil dimers. Subunit composition, assembly, and end-to-end interaction. J. Biol. Chem. 266, 5891-5897. 

Singh, A., and Hitchcock-DeGregori, S. E. (2003). Local destabilization of the tropomyosin coiled-coil gives the molecular flexibility required for actin binding. Biochemistry 42, 14114-14121. 

C and D. These proteins are discussed further in Section 4. Figure 19-9 shows a model of the thin filaments with tropomyosin coiled-coil molecules on each side. The troponin subunits are not shown. 

By examining the amino add sequence of tropomyosin, the smallest and simplest proteins postulated at the time 1819 to contain the coiled-coil motif, we identified the hydrophobic repeat responsible for the formation and stabilization of the coiled-coil structure. 18 A coiled coil can be considered as a repeating heptad of seven amino acid residues a-b-c-d-e-f-g, where positions a and d are occupied by hydrophobic residues. This 3-4 (or 4-3) hydro-... 

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... 

A second widely used sequence-based approach relies on matrices of residue frequencies, pioneered by Parry (1982). He showed that the residue distribution at the seven heptad positions of the putative coiled-coil segments of myosin, tropomyosin, o-keratin, and hemaglutinin are asymmetric, and proposed a method by which the residue frequencies could be used to predict whether a sequence of unknown structure would form a coiled coil. This approach was implemented with modifications in... 

Comparative analyses of the number of favorable interactions in various arrangements have been made to distinguish the register and oligomer specificity of coiled coils, such as tropomyosin (McLachlan and Stewart,... 

Historically, coiled coils were identified with long fibrous molecules, from which their structural properties had been determined. Fiber diffraction studies on proteins of the k-m-e-f class were highly successful, initially on dried specimens but later also on native samples (Cohen and Holmes, 1963). However, these proteins turned out to be very difficult to analyze by high-resolution X-ray crystallography for the same reasons that made them so amenable to fiber diffraction—their tendency to aggregate into fibers rather than crystals and the extreme dimensions of their asymmetric units. It took decades to obtain a working structure for tropomyosin [at 15 A resolution (Phillips et al., 1986) at 9 A (Whitby et al.,... 

Regulation of coiled-coil assembly in tropomyosins./. Struct. Biol. 137, 176-183. Arndt, K. M., Pelletier, J. N., Muller, K. M., Alber, T., Michnick, S. W., and Pliickthun, A. (2000). A heterodimeric coiled-coil peptide pair selected in vivo from a designed library-versus-library ensemble./. Mol. Biol. 295, 627-639. 

Hodges, R. S., Saund, A. K., Chong, P. C. S., Stpierre, S. A., and Reid, R. E. (1981). Synthetic model for 2-stranded alpha-helical coiled-coils - design, synthesis, and characterization of an 86-residue analog of tropomyosin. / Biol. Chem. 256, 1214-1224. 

Talbot, J. A., and Hodges, R. S. (1982). Tropomyosin - A model protein for studying coiled-coil and alpha-helix stabilization. Ace. Chem. Res. 15, 224—230. 

Sodek, J., Hodges, R. S., Smillie, L. B., andjurasek, L. (1972). Amino acid sequence of rabbit skeletal tropomyosin and its coiled-coil structures. Proc. Nat. Acad. Sci. USA 69, 3800-3804. 

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