Mapping the interacting regions between troponins T and C - Binding of TnTand TnI peptides to TnC and NMR mapping of the TnT-binding site on TnC

Muscular contraction is triggered by an increase in calcium concentration, which is transmitted to the contractile proteins by the troponin complex. T he interactions among the components of the troponin complex (troponins T, C, and I) are essential to understanding the regulation of muscle contracti on. While the structure of TnC is well known, and a model for the binary Tn C.TnI complex has been recently published (Tung, C.-S., Wall, M. E., Gallag her, S. C., and Trewhella, J. (2000) Protein Sci. 9, 1312-1326), very littl e is known about TnT. Using non-denaturing gels and NMR spectroscopy, we ha ve analyzed the interactions between TnC and five peptides from TnT as well as how three TnI peptides affect these interactions. Rabbit fast skeletal muscle peptide TnT-(160-193) binds to TnC with a dissociation constant of 3 0 +/- 6 mum. This binding still occurs in the presence of TnI-(1-40) but is prevented by the presence of TnI-(56-115) or TnI-(96-139), both containing the primary inhibitory region of TnI. TnT-(228-260) also binds TnC. The bi nding site for TnT-(160-193) is located on the C-terminal domain of TnC and was mapped to the surface of TnC using NMR chemical shift mapping techniqu es. In the context of the model for the TnC.TnI complex, we discuss the int eractions between TnT and the other troponin subunits.