Effects of Leu43Pro Mutation in the TPM1 Gene on the Structure and Properties of Cardiac Tropomyosin

We investigated the effect of the Leu43Pro mutation in the TPM1 gene encoding the cardiac tropomyosin isoform on the structure and properties of the tropomyosin molecule. For this purpose, we obtained a recombinant tropomyosin preparation with the L43P amino acid substitution in both α-chains of the tropomyosin double superhelix, i.e. with the substitution of the canonical Leu43 residues by the non-canonical Pro residues, and studied the effect of this substitution on the structural and functional properties of tropomyosin. Circular dichroism spectroscopy showed that the L43P substitution significantly disrupts the α-helical structure of the tropomyosin molecule. Differential scanning calorimetry showed that this amino acid substitution causes serious changes in the domain structure of the tropomyosin molecule, leading to significant destabilization of the N-terminal part of the molecule. Measurements of the viscosity of tropomyosin solutions showed that the L43P substitution reduced the viscosity of tropomyosin by more than 7 times compared to the viscosity of the control wild type tropomyosin preparation. It was found, using the method of co-precipitation of tropomyosin with F-actin, that the L43P substitution significantly reduced the affinity of tropomyosin for F-actin. The data obtained clearly indicate that the L43P substitution in both α-chains of the double helix of the tropomyosin molecule significantly changes both the structure of the molecule and the functional properties of cardiac tropomyosin.