Abstract
At least four isoforms of troponin T (TnT) exist in the human heart, and they are expressed in a developmentally regulated manner. To determine whether the different N-terminal isoforms are functionally distinct with respect to structure, Ca2+ sensitivity, and inhibition of force development, the four known human cardiac troponin T isoforms, TnT1 (all exons present), TnT2 (missing exon 4), TnT3 (missing exon 5), and TnT4 (missing exons 4 and 5), were expressed, purified, and utilized in skinned fiber studies and in reconstituted actomyosin ATPase assays. TnT3, the adult isoform, had a slightly higher α-helical content than the other three isoforms. The variable region in the N terminus of cardiac TnT was found to contribute to the determination of the Ca2+ sensitivity of force development in a charge-dependent manner; the greater the charge the higher the Ca2+ sensitivity, and this was primarily because of exon 5. These studies also demonstrated that removal of either exon 4 or exon 5 from TnT increased the cooperativity of the pCa force relationship. Troponin complexes reconstituted with the four TnT isoforms all yielded the same maximal actin-tropomyosin-activated myosin ATPase activity. However, troponin complexes containing either TnT1 or TnT2 (both containing exon 5) had a reduced ability to inhibit this ATPase activity when compared with wild type troponin (which contains TnT3). Interestingly, fibers containing these isoforms also showed less relaxation suggesting that exon 5 of cardiac TnT affects the ability of Tn to inhibit force development and ATPase activity. These results suggest that the different N-terminal TnT isoforms would produce different functional properties in the heart that would directly affect myocardial contraction.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 35341-35349 |
| Number of pages | 9 |
| Journal | Journal of Biological Chemistry |
| Volume | 277 |
| Issue number | 38 |
| DOIs | |
| State | Published - Sep 20 2002 |
| Externally published | Yes |
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ASJC Scopus subject areas
- Biochemistry
Cite this
Cardiac troponin T isoforms affect the Ca2+ sensitivity and inhibition of force development : Insights into the role of troponin T isoforms in the heart. / Gomes, Aldrin V; Guzman, Georgianna; Zhao, Jiaju; Potter, James D.
In: Journal of Biological Chemistry, Vol. 277, No. 38, 20.09.2002, p. 35341-35349.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Cardiac troponin T isoforms affect the Ca2+ sensitivity and inhibition of force development
T2 - Insights into the role of troponin T isoforms in the heart
AU - Gomes, Aldrin V
AU - Guzman, Georgianna
AU - Zhao, Jiaju
AU - Potter, James D.
PY - 2002/9/20
Y1 - 2002/9/20
N2 - At least four isoforms of troponin T (TnT) exist in the human heart, and they are expressed in a developmentally regulated manner. To determine whether the different N-terminal isoforms are functionally distinct with respect to structure, Ca2+ sensitivity, and inhibition of force development, the four known human cardiac troponin T isoforms, TnT1 (all exons present), TnT2 (missing exon 4), TnT3 (missing exon 5), and TnT4 (missing exons 4 and 5), were expressed, purified, and utilized in skinned fiber studies and in reconstituted actomyosin ATPase assays. TnT3, the adult isoform, had a slightly higher α-helical content than the other three isoforms. The variable region in the N terminus of cardiac TnT was found to contribute to the determination of the Ca2+ sensitivity of force development in a charge-dependent manner; the greater the charge the higher the Ca2+ sensitivity, and this was primarily because of exon 5. These studies also demonstrated that removal of either exon 4 or exon 5 from TnT increased the cooperativity of the pCa force relationship. Troponin complexes reconstituted with the four TnT isoforms all yielded the same maximal actin-tropomyosin-activated myosin ATPase activity. However, troponin complexes containing either TnT1 or TnT2 (both containing exon 5) had a reduced ability to inhibit this ATPase activity when compared with wild type troponin (which contains TnT3). Interestingly, fibers containing these isoforms also showed less relaxation suggesting that exon 5 of cardiac TnT affects the ability of Tn to inhibit force development and ATPase activity. These results suggest that the different N-terminal TnT isoforms would produce different functional properties in the heart that would directly affect myocardial contraction.
AB - At least four isoforms of troponin T (TnT) exist in the human heart, and they are expressed in a developmentally regulated manner. To determine whether the different N-terminal isoforms are functionally distinct with respect to structure, Ca2+ sensitivity, and inhibition of force development, the four known human cardiac troponin T isoforms, TnT1 (all exons present), TnT2 (missing exon 4), TnT3 (missing exon 5), and TnT4 (missing exons 4 and 5), were expressed, purified, and utilized in skinned fiber studies and in reconstituted actomyosin ATPase assays. TnT3, the adult isoform, had a slightly higher α-helical content than the other three isoforms. The variable region in the N terminus of cardiac TnT was found to contribute to the determination of the Ca2+ sensitivity of force development in a charge-dependent manner; the greater the charge the higher the Ca2+ sensitivity, and this was primarily because of exon 5. These studies also demonstrated that removal of either exon 4 or exon 5 from TnT increased the cooperativity of the pCa force relationship. Troponin complexes reconstituted with the four TnT isoforms all yielded the same maximal actin-tropomyosin-activated myosin ATPase activity. However, troponin complexes containing either TnT1 or TnT2 (both containing exon 5) had a reduced ability to inhibit this ATPase activity when compared with wild type troponin (which contains TnT3). Interestingly, fibers containing these isoforms also showed less relaxation suggesting that exon 5 of cardiac TnT affects the ability of Tn to inhibit force development and ATPase activity. These results suggest that the different N-terminal TnT isoforms would produce different functional properties in the heart that would directly affect myocardial contraction.
UR - http://www.scopus.com/inward/record.url?scp=0037144508&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=0037144508&partnerID=8YFLogxK
U2 - 10.1074/jbc.M204118200
DO - 10.1074/jbc.M204118200
M3 - Article
C2 - 12093807
AN - SCOPUS:0037144508
VL - 277
SP - 35341
EP - 35349
JO - Journal of Biological Chemistry
JF - Journal of Biological Chemistry
SN - 0021-9258
IS - 38
ER -