Altered regulatory function of two familial hypertrophic cardiomyopathy troponin T mutants.
Mutations in the gene encoding human cardiac troponin T can cause familial hypertrophic cardiomyopathy, a disease that is characterized by ventricular hypertrophy and sudden, premature death. Troponin T is the tropomyosin-binding subunit of troponin required for thin filament regulation of contraction. One mutation, a change in the intron 15 splice donor site, results in two truncated forms of troponin T [Thierfelder et al. (1994) Cell 77, 701-712]. In one form, the mRNA skips exon 16 that encodes the C-terminal 14 amino acids; in the other, seven novel residues replace the exon 15- and 16-encoded C-terminal 28 amino acids. The two troponin T cDNAs were expressed in Escherichia coli for functional analysis. Both C-terminal deletion mutants formed a complex with cardiac troponin C and troponin I that exhibited the same concentration dependence as wild-type for regulation of the actomyosin MgATPase. However, both mutants showed severely reduced activation of the regulated actomyosin in the presence of Ca2+, though the inhibition in the absence of Ca2+ and the Ca(2+)-dependence of activation were not altered. The C-terminal deletions reduce the effectiveness of Ca(2+)-troponin to switch the thin filament from the "off" to the "on" state. Both mutant troponin Ts have reduced affinity for troponin I; the shorter mutant is at least 6-fold weaker than wild-type. The low level of activation of the ATPase would be consistent with reduced contractile performance, and the results suggest reduced troponin I affinity may be the molecular basis for the disease.
Mukherjea
P
P
Department of Neuroscience and Cell Biology, Robert Wood Johnson Medical School, Piscataway, New Jersey 08854, USA.
Tong
L
L
Seidman
J G
JG
Seidman
C E
CE
Hitchcock-DeGregori
S E
SE
D000595:Amino Acid Sequence; D000818:Animals; D002118:Calcium / Q000502:physiology; D002312:Cardiomyopathy, Hypertrophic / Q000201:enzymology / Q000235:genetics* / Q000378:metabolism*; D004789:Enzyme Activation / Q000235:genetics; D006801:Humans; D008969:Molecular Sequence Data; D009206:Myocardium / Q000201:enzymology / Q000378:metabolism; D009218:Myosins / Q000037:antagonists & inhibitors / Q000378:metabolism; D010446:Peptide Fragments / Q000235:genetics / Q000378:metabolism; D011485:Protein Binding / Q000235:genetics; D051381:Rats; D017384:Sequence Deletion; D019210:Troponin I / Q000378:metabolism; D020107:Troponin T / Q000235:genetics* / Q000502:physiology
D010446:Peptide Fragments; D019210:Troponin I; D020107:Troponin T; D009218:Myosins; D002118:Calcium