Effects of two stabilizing substitutions, D137L and G126R, in the middle part of α-tropomyosin on the domain structure of its molecule

We applied differential scanning calorimetry (DSC) to investigate the effects of substitutions D137L and G126R (i.e. replacement of conserved non-canonical residues Asp137 and Gly126 by canonical ones) in the middle part of tropomyosin (Tm), as well as the combined one, D137L/G126R, on the thermal unfolding of Tm. Special approaches (e.g. combination of DSC with measurements of temperature dependences of pyrene excimer fluorescence) were applied to assign separate thermal transitions (calorimetric domains) on the DSC profiles to the certain parts of Tm molecule. The results show that substitutions D137L and G126R (and, especially, the combined one, D137L/G126R) may stabilize not only the middle region of Tm, but also the other parts of its molecule including N- and C-terminal parts. These results suggest that the stabilization of the Tm middle part can be transmitted along the coiled-coil length displaying long-range effects. [Display omitted] •Non-canonical residues D137 and G126 destabilize the middle part of tropomyosin (Tm).•These residues were replaced by canonical ones by mutations D137L and G126R.•We applied DSC to study the effects of these mutations on the Tm thermal unfolding.•These mutations (especially D137L/G126R) dramatically alter the Tm domain structure.•Stabilization of Tm middle part can be transmitted to other parts of the molecule.