The presence but not the sequence of the N-terminal peptide in cardiac TnC is important for function.
The most diverged region of the primary amino acid sequence between cardiac (cTnC) and fast skeletal troponin C is the N-terminal ten amino acids. We report here that major changes in the primary sequence of this region in cTnC had a minimal effect on the ability of the mutant proteins to recover maximal activity in TnC-extracted cardiac and fast skeletal muscle myofibrils. However, deletion of the N-terminal nine amino acids resulted in a 60% decrease in maximal Ca(2+)-dependent ATPase activity with only a small change in the pCa50 of activation. Deletion of the N-terminal peptide did not appear to appreciably affect the Ca(2+)-binding properties of cTnC, but it did alter the interaction with hydrophobic fluorescent probes. Thus, the presence but not the sequence, of the N-terminal extension is important for the maximal activity of cTnC. The N-terminal helix may function in a relatively non-specific manner to prevent unfavorable interactions between domains in cTnC or between cTnC and other troponin subunits.
Department of Biochemistry and Molecular Biology, University of Texas Medical School, Houston 77030.
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W
Liu
D G
DG
Dotson
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Lin
J J
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Mullen
M L
ML
Gonzalez-Garay
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Lu
J A
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Putkey
D000251:Adenosine Triphosphatases / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology; D002645:Chickens; D005453:Fluorescence; D008969:Molecular Sequence Data; D009132:Muscles / Q000378:metabolism; D016296:Mutagenesis; D009206:Myocardium / Q000737:chemistry* / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry; D013329:Structure-Activity Relationship; D014336:Troponin / Q000737:chemistry* / Q000235:genetics / Q000502:physiology; D019209:Troponin C; D014443:Tyrosine / Q000737:chemistry
D011994:Recombinant Proteins; D014336:Troponin; D019209:Troponin C; D014443:Tyrosine; D000251:Adenosine Triphosphatases; D002118:Calcium