Disease-causing mutations in cardiac troponin T: identification of a critical tropomyosin-binding region

Area of Science:

• Cardiovascular Genetics
• Molecular Cardiology
• Protein Biochemistry

Background:

• Familial hypertrophic cardiomyopathy (HCM) is a genetic heart disease.
• Mutations in the troponin T gene account for 15% of HCM cases.
• Many HCM-associated troponin T mutations cluster in a region interacting with tropomyosin.

Purpose of the Study:

• To investigate the functional impact of specific troponin T mutations on tropomyosin binding and muscle regulation.
• To elucidate the molecular mechanisms by which troponin T mutations cause HCM.

Main Methods:

• Site-directed mutagenesis was used to introduce nine mutations into a troponin T fragment (Gly-hcTnT(70-170)).
• Assessed tropomyosin binding affinity using an affinity column.
• Evaluated the stabilization of tropomyosin overlap complexes and tropomyosin-actin binding promotion.
• Measured troponin T stability using circular dichroism.

Main Results:

• Mutations between residues 92-110 impaired tropomyosin-dependent functions, including reduced binding to tropomyosin and less effective promotion of tropomyosin-actin binding.
• These mutants showed decreased stabilization of the tropomyosin overlap complex, correlating with increased troponin T stability.
• Mutations outside this region (residues 79, 160, 163) did not affect these functions.

Conclusions:

• Mutations within the 92-110 region of troponin T likely cause HCM through altered interactions with tropomyosin.
• These alterations disrupt the critical overlap region, affecting cooperative actin binding and muscle regulatory function.
• A model for the five-chained coiled-coil structure of troponin T in the tropomyosin overlap complex is proposed.