TAILIEUCHUNG - Báo cáo khoa học: The calcium-induced switch in the troponin complex probed by fluorescent mutants of troponin I

The Ca 2+ -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 Ca 2+ binding to the regulatoryN-domain of TnC are the inhibitoryregion (residues 96–116) and a neighboring region that includes position 121. Our data confirms the role of TnI as a modulator of the Ca 2+ affinityof TnC; we show that point mutations and incorporation of 5HWinTnI can affect both the affinityand the cooperativityof Ca 2+ binding to TnC | Eur. J. Biochem. 270 2937-2944 2003 FEBS 2003 doi The calcium-induced switch in the troponin complex probed by fluorescent mutants of troponin I Deodoro C. S. G. Oliveira and Fernando C. Reinach Departamento de Bioquimica Instituto de Quimica Universidade de Scio Paulo Brazil 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-domaín of TnC are the iihiibiorry region residues 96-116 and a neighboring region that includes position 121. Our data confirms the role of ToI as a modulator of the Ca2 affinity rf TnC we show Uicu ỊSO0it mutations and incorporation of 5HW in TnI can affect both the affinityand the cooperativityof Ca 2 binding to TnC. We also discuss the possibilitythat the regulatorysites in the N-terminal domain of TnC might be the high affinity Ca2 -binding sites in the troponin complex. Keywords 5-hydroxytryptophan Ca2 -binding protein fluorescence troponin skeletal muscle. The regulation of striated muscle contraction in vertebrates is accomplished by troponin Tn a protein associated with actin in the thin filament. Tn is a complex composed of three polypeptide subunits troponin C TnC has the Ca2 -binding sites troponin I TnI has the inhibitory I unciion. and troponin T TnT is the actin-tropomyosin-binding component. Tn works as a sensor of intracellular calcium concentration. Stimulation of the muscle leads to Ca2 increase and Ca2 binding to TnC removes the inhibition of the muscle contraction promoted byTnI. The conformational transition undergone byTn enables the regulation of muscle contraction 1-3 . TnC has two globular domains connected by an a-helix and each domain has two Ca2 -binding sites EF-hand motifs 4 . The Ca2

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