Elucidating the Molecular and Functional Effects of Tropomyosin Mutations Associated with Left Ventricular Non-Compaction

Genetic forms of left ventricular non-compaction (LVNC) have been linked to variants in numerous genes, including those encoding sarcomeric proteins, but the underlying molecular mechanisms remain poorly understood. Here, we investigated the structural and functional effects of three LVNC-associated variants, L113V, D159N, and R160H, in the TPM1 gene, which encodes α-tropomyosin (Tpm), a major tropomyosin isoform in the heart. Using recombinant proteins, we characterized these variants by differential scanning calorimetry, co-sedimentation with filamentous actin, viscometry, light scattering, in vitro motility assays, and molecular dynamics simulations. All three variants impaired actin–myosin interactions in vitro using both atrial and ventricular myosin. L113V markedly reduced motility of F-actin–Tpm filaments, possibly due to increased Tpm flexibility. The D159N and R160H variants decreased Ca2+ sensitivity and/or maximum sliding velocity of reconstituted thin filaments over both atrial and ventricular myosin, presumably by altering Tpm interactions with actin and troponin I. Thus, the L113V, D159N, and R160H variants alter the structural and functional properties of Tpm in ways that may contribute to LVNC development.