Cardiac troponin C-L29Q, related to hypertrophic cardiomyopathy, hinders the transduction of the protein kinase A dependent phosphorylation signal from cardiac troponin I to C.
We investigated structural and functional aspects of the first mutation in TNNC1, coding for the calcium-binding subunit (cTnC) of cardiac troponin, which was detected in a patient with hypertrophic cardiomyopathy [ Hoffmann B, Schmidt-Traub H, Perrot A, Osterziel KJ & Gessner R (2001) Hum Mut17, 524]. This mutation leads to a leucine-glutamine exchange at position 29 in the nonfunctional calcium-binding site of cTnC. Interestingly, the mutation is located in a putative interaction site for the nonphosphorylated N-terminal arm of cardiac troponin I (cTnI) [ Finley NL, Abbott MB, Abusamhadneh E, Gaponenko V, Dong W, Seabrook G, Howarth JW, Rana M, Solaro RJ, Cheung HC et al. (1999) EJB Lett453, 107-112]. According to peptide array experiments, the nonphosphorylated cTnI arm interacts with cTnC around L29. This interaction is almost abolished by L29Q, as observed upon protein kinase A-dependent phosphorylation of cTnI at serine 22 and serine 23 in wild-type troponin. With CD spectroscopy, minor changes are observed in the backbone of Ca2+-free and Ca2+-saturated cTnC upon the L29Q replacement. A small, but significant, reduction in calcium sensitivity was detected upon measuring the Ca2+-dependent actomyosin subfragment 1 (actoS1)-ATPase activity and the sliding velocity of thin filaments. The maximum actoS1-ATPase activity, but not the maximum sliding velocity, was significantly enhanced. In addition, we performed our investigations at different levels of protein kinase A-dependent phosphorylation of cTnI. The in vitro assays mainly showed that the Ca2+ sensitivity of the actoS1-ATPase activity, and the mean sliding velocity of thin filaments, were no longer affected by protein kinase A-dependent phosphorylation of cTnI owing to the L29Q exchange in cTnC. The findings imply a hindered transduction of the phosphorylation signal from cTnI to cTnC.
Schmidtmann
Anja
A
Herz- und Kreislaufzentrum der Ruhr-Universität Bochum/Bergmannsheil, Forschungslabor Molekulare Kardiologie, Bochum, Germany.
Lindow
Christopher
C
Villard
Sylvie
S
Heuser
Arnd
A
Mügge
Andreas
A
Gessner
Reinhard
R
Granier
Claude
C
Jaquet
Kornelia
K
D000595:Amino Acid Sequence; D002118:Calcium / Q000378:metabolism; D002312:Cardiomyopathy, Hypertrophic / Q000235:genetics / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D004252:DNA Mutational Analysis; D006801:Humans; D008969:Molecular Sequence Data; D009206:Myocardium / Q000737:chemistry*; D010455:Peptides / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation; D017354:Point Mutation; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*; D019209:Troponin C / Q000235:genetics* / Q000378:metabolism*; D019210:Troponin I / Q000378:metabolism*
D010455:Peptides; D021122:Protein Subunits; D011994:Recombinant Proteins; D019209:Troponin C; D019210:Troponin I; D017868:Cyclic AMP-Dependent Protein Kinases; D002118:Calcium