TY - JOUR
T1 - Cooperative interaction between developmentally regulated troponin T and tropomyosin isoforms in the absence of F-actin
AU - Ogut, Ozgur
AU - Jin, Jian Ping
PY - 2000/8/25
Y1 - 2000/8/25
N2 - Troponin T (TnT) is the tropomyosin (Tm) binding subunit of the troponin complex that mediates the Ca2+ regulation of actomyosin interaction in striated muscles. Troponin T isoform diversity is marked by a developmentally regulated acidic to basic switch that may modulate muscle contractility. We previously reported that transgenic expression of fast skeletal muscle TnT altered the cooperativity of cardiac muscle. In the present study, we have demonstrated that the binding of acidic TnT to troponin I is weaker than that of basic TnT. However, affinity chromatography experiments showed that Tm bound to acidic TnT with a greater affinity than to basic TnT, consistent with the significantly higher maximal binding of acidic TnT to Tm in solid phase binding assays. Competition and co-immunoprecipitation experiments demonstrated that the binding of TnT to Tm was cooperative in the absence of F-actin. The cooperativity between TnT molecules for Tm binding can be initiated by the conserved COOH-terminal T2 fragment of TnT. This indicates that the interaction of TnT with Tm induces a conformational change in Tm, promoting interaction of TnT with adjacent Tm dimers. This finding suggests a role for TnT and its acidic and basic isoforms in the cooperative release of the inhibition of striated muscle actomyosin interaction.
AB - Troponin T (TnT) is the tropomyosin (Tm) binding subunit of the troponin complex that mediates the Ca2+ regulation of actomyosin interaction in striated muscles. Troponin T isoform diversity is marked by a developmentally regulated acidic to basic switch that may modulate muscle contractility. We previously reported that transgenic expression of fast skeletal muscle TnT altered the cooperativity of cardiac muscle. In the present study, we have demonstrated that the binding of acidic TnT to troponin I is weaker than that of basic TnT. However, affinity chromatography experiments showed that Tm bound to acidic TnT with a greater affinity than to basic TnT, consistent with the significantly higher maximal binding of acidic TnT to Tm in solid phase binding assays. Competition and co-immunoprecipitation experiments demonstrated that the binding of TnT to Tm was cooperative in the absence of F-actin. The cooperativity between TnT molecules for Tm binding can be initiated by the conserved COOH-terminal T2 fragment of TnT. This indicates that the interaction of TnT with Tm induces a conformational change in Tm, promoting interaction of TnT with adjacent Tm dimers. This finding suggests a role for TnT and its acidic and basic isoforms in the cooperative release of the inhibition of striated muscle actomyosin interaction.
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U2 - 10.1074/jbc.M910360199
DO - 10.1074/jbc.M910360199
M3 - Article
C2 - 10844003
AN - SCOPUS:0034714195
SN - 0021-9258
VL - 275
SP - 26089
EP - 26095
JO - Journal of Biological Chemistry
JF - Journal of Biological Chemistry
IS - 34
ER -