Cardiomyopathy-Associated Mutation K15N in Tropomyosin Affects its Interaction with Leiomodin and Tropomodulin

Abstract

The development of some familial dilated cardiomyopathies (DCM ) correlates with the presence of mutations in proteins that regulate the organization and function of thin filaments in cardiac muscle cells. Whereas the biological consequence of mutations affecting protein folding, stability and levels of intracellular expression is more apparent, understanding of harmful effects of mutations interfering with yet uncharacterized protein-protein interactions might be elusive. We used nuclear magnetic resonance spectroscopy to precisely localize the region of striated muscle α-tropomyosin that interacts with leiomodin-2 (Lmod2), a member of tropomodulin family of actin-binding proteins. The K15N mutation known to be associated with familial DCM is located within the newly identified Lmod2 binding site of tropomyosin. We studied the effect of this mutation on binding Lmod2 and Tmod1, cardiac isoforms responsible for correct lengths of the thin filaments. The mutation reduced binding affinity for both Lmod2 and Tmod1, however the decrease was more pronounced for binding Lmod2. The reduced affinity and the uneven effect of the K15N mutation on TM binding to Lmod2 and Tmod1 provide a molecular rationale for the development of familial DCM.