Altered signaling surrounding the C-lobe of cardiac troponin C in myofilaments containing an alpha-tropomyosin mutation linked to familial hypertrophic cardiomyopathy.
A region of interaction between the near N-terminal of cardiac troponin I (cTnI) and the C-lobe of troponin C (cTnC), where troponin T (cTnT) binds, appears to be critical in regulation of myofilament Ca(2+)-activation. We probed whether functional consequences of modulation of this interface influence the function of tropomyosin (Tm) in thin filament activation. We modified the C-lobe of cTnC directly by addition of the Ca(2+)-sensitizer, EMD 57033, and indirectly by replacing native cTnI with cTnI-containing Glu residues at Ser-43 and Ser-45 (cTnI-S43E/S45E) in myofilaments from hearts of non-transgenic (NTG) and transgenic (TG) mice expressing a point mutation on alpha-Tm (E180G) linked to familial hypertrophic cardiomyopathy. Introduction of cTnI-S43E/S45E induced a significantly greater reduction in tension in TG myofilaments compared to NTG controls. Furthermore, the effect of EMD 57033 to restore Ca(2+)-sensitivity was higher in TG compared to NTG fiber bundles containing cTnI-S43E/S45E and compared to TG or NTG fiber bundles containing native TnI. Our results indicate that alterations in regions of interaction among the N-terminal of cTnI, the C-lobe of cTnC, and the C-terminus of cTnT are important in the regulation of myofilament activity. Although levels of phosphorylation at protein kinase C-dependent sites were the same in TG and NTG myofilaments, our data indicate that the effects of phosphorylation were more depressive in TG hearts.
D000818:Animals; D015153:Blotting, Western; D002118:Calcium / Q000378:metabolism; D024741:Cardiomyopathy, Hypertrophic, Familial / Q000235:genetics*; D004305:Dose-Response Relationship, Drug; D004591:Electrophoresis, Polyacrylamide Gel; D018698:Glutamic Acid / Q000737:chemistry; D051379:Mice; D008822:Mice, Transgenic; D018485:Muscle Fibers, Skeletal / Q000378:metabolism; D009154:Mutation; D009206:Myocardium / Q000378:metabolism*; D010766:Phosphorylation; D011485:Protein Binding; D011493:Protein Kinase C / Q000378:metabolism; D017434:Protein Structure, Tertiary; D011804:Quinolines / Q000494:pharmacology; D012694:Serine / Q000737:chemistry; D015398:Signal Transduction; D013829:Thiadiazines / Q000494:pharmacology; D013997:Time Factors; D014335:Tropomyosin / Q000235:genetics*; D019209:Troponin C / Q000737:chemistry*
D011804:Quinolines; D013829:Thiadiazines; D014335:Tropomyosin; D019209:Troponin C; C070609:EMD 53998; D018698:Glutamic Acid; D012694:Serine; D011493:Protein Kinase C; D002118:Calcium