Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.6.4.1 (myosin ATPase)
 1,140 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Familial hypertrophic cardiomyopathy (HCM) is caused by mutations in at least 8 contractile protein genes, most commonly beta myosin heavy chain, myosin binding protein C, and cardiac troponin T. Affected individuals are heterozygous for a particular mutation, and most evidence suggests that the mutant protein acts in a dominant-negative fashion. To investigate the functional properties of a truncated troponin T shown to cause HCM, both wild-type and mutant human cardiac troponin T were overexpressed in Escherichia coli, purified, and combined with human cardiac troponins I and C to reconstitute human cardiac troponin. Significant differences were found between the regulatory properties of wild-type and mutant troponin in vitro, as follows. (1) In actin-tropomyosin-activated myosin ATPase assays at pCa 9, wild-type troponin caused 80% inhibition of ATPase, whereas the mutant complex gave negligible inhibition. (2) Similarly, in the in vitro motility assay, mutant troponin failed to decrease both the proportion of actin-tropomyosin filaments motile and the velocity of motile filaments at pCa 9. (3) At pCa 5, the addition of mutant complex caused a greater increase (21.7%) in velocity of actin-tropomyosin filaments than wild-type troponin (12.3%). These data suggest that the truncated troponin T prevents switching off of the thin filament at low Ca(2+). However, the study of thin filaments containing varying ratios of wild-type and mutant troponin T at low Ca(2+) indicated an opposite effect of mutant troponin, causing enhancement of the inhibitory effect of wild-type complex, when it is present in a low ratio (10% to 50%). These multiple effects need to be taken into account to explain the physiological consequences of this mutation in HCM. Further, these findings underscore the importance of studying mixed mutant:wild-type preparations to faithfully model this autosomal-dominant disease.
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PMID:Investigation of a truncated cardiac troponin T that causes familial hypertrophic cardiomyopathy: Ca(2+) regulatory properties of reconstituted thin filaments depend on the ratio of mutant to wild-type protein. 1085 Sep 66

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, Ca(2+) 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 alpha-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 Ca(2+) sensitivity of force development in a charge-dependent manner; the greater the charge the higher the Ca(2+) 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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PMID:Cardiac troponin T isoforms affect the Ca2+ sensitivity and inhibition of force development. Insights into the role of troponin T isoforms in the heart. 1209 7