Fluorescence analysis of troponin I mutants containing 5-hydroxytryptophan demonstrated that the inhibitory region and position 121 respond to Ca2+ binding to the regulatory N-domain of TnC.
The study identifies specific regions in troponin I that respond to calcium binding and demonstrates its role as a modulator of calcium affinity in the troponin complex.
The Ca2+-induced transition in the troponin complex (Tn) regulates vertebrate striated muscle contraction. Tn was reconstituted with recombinant forms of troponin I (TnI) containing a single intrinsic 5-hydroxytryptophan (5HW). Fluorescence analysis of these mutants of TnI demonstrate that the regions in TnI that respond to Ca2+ binding to the regulatory N-domain of TnC are the inhibitory region (residues 96-116) and a neighboring region that includes position 121. Our data confirms the role of TnI as a modulator of the Ca2+ affinity of TnC; we show that point mutations and incorporation of 5HW in TnI can affect both the affinity and the cooperativity of Ca2+ binding to TnC. We also discuss the possibility that the regulatory sites in the N-terminal domain of TnC might be the high affinity Ca2+-binding sites in the troponin complex.
Oliveira et al. (Tue,) reported a other. Recombinant forms of troponin I containing a single intrinsic 5-hydroxytryptophan (5HW) was evaluated on Ca2+ binding response and affinity. Fluorescence analysis of troponin I mutants containing 5-hydroxytryptophan demonstrated that the inhibitory region and position 121 respond to Ca2+ binding to the regulatory N-domain of TnC.
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