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|Title:||Structure of Cocrystals of Tropomyosin and Troponin|
|Author(s):||White, Steven Paul|
|Doctoral Committee Chair(s):||Phillips, George N., Jr.,|
|Department / Program:||Biochemistry|
|Degree Granting Institution:||University of Illinois at Urbana-Champaign|
|Abstract:||The contraction of vertebrate striated muscle is controlled by proteins found in the thin filament. Contraction is initiated when calcium binds to troponin, causing it and tropomyosin to undergo conformational changes. Tropomyosin is an $\alpha$-helical protein with two chains (284 residues each) arranged as a coiled-coil. These rod-like molecules form cables wound in the grooves of the actin helix. Bound to each tropomyosin molecule is a troponin complex, consisting of three subunits, each with a different architecture and function. Troponin C binds calcium; troponin I binds actin; and troponin T (259 residues) binds one complex to each tropomyosin molecule. The troponin complex has an elongated shape with troponin C and troponin I forming a globular 'head' region and troponin T a long ($\sim$160 A) tail. This study visualizes the interactions between tropomyosin and troponin using X-ray crystallography.
Tropomyosin crystals are unusually labile and are treated with glutaraldehyde to stabilize them. Troponin and its fragments can then be diffused into the tropomyosin lattice and the structure of the resulting cocrystals are solved, based on previous structural studies of tropomyosin. Whole troponin, a complex of troponin T with troponin C, and two fragments of the troponin tail domain (residues 1-158 and 71-151 of troponin T) have been incorporated and visualized to 20 A resolution.
The results show how tropomyosin and troponin interact with one another. Part of the tail of troponin consisting of the N-terminal section of troponin T lies along the carboxy end of tropomyosin from residues 235-284. It also interacts with a short segment of the adjacent tropomyosin molecule. Residues 1-71 of troponin T are involved in binding to the termini of tropomyosin and residues 71-151 extend toward the middle of the tropomyosin molecule up to residue 235. The globular domain of troponin binds near amino acids 150-180 of the tropomyosin molecule. These results define interactions in the thin filament which will be useful in elucidating the roles of these proteins in the regulation of muscle contraction.
Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1988.
|Date Available in IDEALS:||2014-12-15|