[HTML][HTML] Structure and interactions of the carboxyl terminus of striated muscle α-tropomyosin: it is important to be flexible

NJ Greenfield, T Palm, SE Hitchcock-DeGregori - Biophysical journal, 2002 - cell.com
Biophysical journal, 2002cell.com
Tropomyosin (TM) binds to and regulates the actin filament. We used circular dichroism and
heteronuclear NMR to investigate the secondary structure and interactions of the C terminus
of striated muscle α-TM, a major functional determinant, using a model peptide, TM9a 251–
284. The 1 H α and 13 C α chemical shift displacements show that residues 252 to 277 are α-
helical but residues 278 to 284 are nonhelical and mobile. The 1 HN and 13 C′
displacements suggest that residues 257 to 269 form a coiled coil. Formation of an" overlap" …
Abstract
Tropomyosin (TM) binds to and regulates the actin filament. We used circular dichroism and heteronuclear NMR to investigate the secondary structure and interactions of the C terminus of striated muscle α-TM, a major functional determinant, using a model peptide, TM9a251–284. The 1Hα and 13Cα chemical shift displacements show that residues 252 to 277 are α-helical but residues 278 to 284 are nonhelical and mobile. The 1HN and 13C′ displacements suggest that residues 257 to 269 form a coiled coil. Formation of an "overlap" binary complex with a 33-residue N-terminal chimeric peptide containing residues 1 to 14 of α-TM perturbs the 1HN and 15N resonances of residues 274 to 284. Addition of a fragment of troponin T, TnT70–170, to the binary complex perturbs most of the 1HN-15N cross-peaks. In addition, there are many new cross-peaks, showing that the binding is asymmetric. Q263, in a proposed troponin T binding site, shows two sets of side-chain 15N-1H cross-peaks, indicating conformational flexibility. The conformational equilibrium of the side chain changes upon formation of the binary and ternary complexes. Replacing Q263 with leucine greatly increases the stability of TM9a251–284 and reduces its ability to form the binary and ternary complexes, showing that conformational flexibility is crucial for the binding functions of the C terminus.
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