DEFINING THE MOLECULAR RELATIONSHIP BETWEEN EX VIVO PROLIFERATED AND IN SITU RESIDENT CARDIAC STEM CELLS

Abstract

the cardiac troponin (cTn) complex. Understanding these mutations is crucial to the accurate diagnosis and development of novel treatments for FHC. The cTn complex contains three proteins: cTnC, a Ca sensor protein; cTnI, an inhibitory protein; and cTnT, a tether to the thin filament. To date six FHC-linked mutations have been found in cTnC, a highly conserved protein that initiates cardiac contraction in response to the cytosolic level of Ca. Upon Ca binding, a hydrophobic patch on cTnC is exposed, which causes the inhibitory peptide of cTnI to withdraw from the actin filament, initiating muscle contraction. Mutations that alter the ability of cTnC to bind Ca are hypothesized to induce either hypertrophic or dilated cardiomyopathies depending on whether Ca affinity is increased or decreased, respectively. METHODS AND RESULTS: The FHC-associated mutations A8V, L29Q and C84Y in the N-terminal domain were studied. The structural effects of these mutations were modeled through molecular dynamics and their functional impact assessed using free energy calculations of the cTnCCa interaction. In each mutant, the equilibrated structures were very similar to those of wild-type (WT), the site II Ca coordination, size of cTnC-Ca interface, and the stability of the structures were consistent. Changes were noted in the angle between helices A and B, indicative of the exposure of the hydrophobic patch. Additionally, a change in the free energy of Ca binding was calculated between the mutant and WT structures. CONCLUSION: The change in free energy due to the cTnCCa interaction was the highest for the A8V mutation, followed by the WT protein, C84Y and finally, L29Q. Only the A8V mutation caused a free energy change in Ca binding that was greater than WT. This is contrary to the hypothesis that higher affinity for Ca is associated with FHC. Interestingly, the degree to which the hydrophobic patch on cTnC was exposed was greater than WT in each of the mutants. Taken together, these results suggest that while the Ca affinity does not change, the energy barrier to transduction of the Ca-binding signal has been lowered in each of the mutated proteins. CIHR