Computational Characterization of Mutations in Cardiac Troponin T Known to Cause Familial Hypertrophic Cardiomyopathy

Abstract

Cardiac Troponin T (cTnT) is a central modulator of thin filament regulation of myofilament activation. The lack of structural data for the TNT1 tail domain, a proposed α-helical region, makes the functional implications of the FHC mutations difficult to determine. Studies have suggested that flexibility of TNT1 is important in normal protein-protein interactions within the thin filament. Our groups have previously shown through Molecular Dynamics (MD) simulations that some FHC mutations, Arg92Leu(R92L) and Arg92Trp(R92W), result in increased flexibility at a critical hinge region 12 residues distant from the mutation. To explain this distant effect and its implications for FHC mutations, we characterized the dynamics of wild type and mutational segments of cTnT using MD. Our data shows an opening of the helix between residues 105-110 in mutants. Consequently, the dihedral angles of these residues correspond to non-α-helical regions on Ramachandran plots. We hypothesize the removal of a charged residue decreases electrostatic repulsion between the point mutation and surrounding residues resulting in local helical compaction. Constrained ends of the helix and localized compaction results in expansion within the nearest non-polar helical turn from the mutation site, residues 105-109.

Keywords: flexibility; molecular dynamics; protein function.

FIG. 1

Models of residues 70–170 of murine cTnT, where hotspot mutation site residue 92 is shown in red and the hinge region, residues 104–110, are shown in purple. Top left, illustration of pitch, p, and rise, m as defined in the text; top right, WT; bottom left, R92L; bottom right, R92W.

FIG. 2

cTnT mutational effects on n-(n+4) distances as a function of time for residues 92–110 WT, R92L, and R92W for 300ps.

FIG. 3

Ramachandran plots for residues 92–110 of average structures for WT, R92L, and R92W cTnT.