Allosteric Transmission along a Loosely Structured Backbone Allows a Cardiac Troponin C Mutant to Function with Only...

Area of Science:

• Biochemistry
• Molecular Biology
• Cardiovascular Research

Background:

• Hypertrophic cardiomyopathy (HCM) is a common inherited heart condition and a leading cause of sudden cardiac death in young individuals.
• Cardiac troponin C (cTnC) acts as the sarcomere's calcium sensor, crucial for regulating muscle contraction.
• Understanding the structural basis of cTnC mutations in HCM is vital for elucidating disease mechanisms.

Purpose of the Study:

• To investigate the structural and functional consequences of a specific cTnC mutation (D145E) associated with HCM.
• To explore the potential allosteric mechanisms underlying the HCM phenotype in mutant cTnC.
• To provide molecular insights into how cTnC mutations contribute to hypertrophic cardiomyopathy.

Main Methods:

• High-resolution electron-spray ionization mass spectrometry (ESI-MS) to analyze protein structure.
• Carr-Purcell-Meiboom-Gill relaxation dispersion (CPMG-RD) to probe protein dynamics.
• Affinity measurements of cTnC for the thin filament in reconstituted papillary muscles.

Main Results:

• The D145E mutation alters cTnC dynamics on the microsecond-to-millisecond timescale.
• This mutation deactivates both divalent cation-binding sites in the cTnC C-domain and reveals a low-populated folding conformation.
• Despite impaired Ca2+ binding in the C-domain, the D145E mutant exhibits increased affinity for thin filaments, suggesting an allosteric effect on the N-domain's Ca2+-binding site II.

Conclusions:

• The D145E mutation in cTnC triggers an allosteric response, increasing Ca2+ affinity in the N-domain.
• This allosteric mechanism provides a molecular explanation for the HCM phenotype.
• Findings offer new insights into the pathogenesis of hypertrophic cardiomyopathy linked to cTnC mutations.