Cardiac troponin T Isoforms affect the Ca2+ sensitivity and inhibition of force development -: Insights into the role of troponin T isoforms in the heart

被引:105
作者
Gomes, AV [1 ]
Guzman, G [1 ]
Zhao, JJ [1 ]
Potter, JD [1 ]
机构
[1] Univ Miami, Sch Med, Dept Mol & Cellular Pharmacol, Miami, FL 33136 USA
关键词
D O I
10.1074/jbc.M204118200
中图分类号
Q5 [生物化学]; Q7 [分子生物学];
学科分类号
071010 ; 081704 ;
摘要
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 a-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.
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页码:35341 / 35349
页数:9
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