tailieunhanh - Báo cáo Y học: Equilibrium unfolding and conformational plasticity of troponin I and T

The structures and stabilities of recombinant chickenmuscle troponin I (TnI) and T (TnT) were investigated by a com-bination of bis-ANS binding and equilibrium unfolding most folded proteins, isolated TnI and TnT bind the hydrophobic fluorescent probe bis-ANS, indicating the existence of solvent-exposed hydrophobic domains in their binding to binary or ternary mix-tures of TnI, TnT and troponin C (TnC) in solution is sig-nificantly lower than binding to the isolated subunits, which can be explained by burial of previously exposed hydro-phobicdomainsuponassociationof the subunits to formthe native troponin complex | Eur. J. Biochem. 269 5484-5491 2002 FEBS 2002 doi Equilibrium unfolding and conformational plasticity of troponin I and T Samantha M. Martins Alex Chapeaurouge and Sergio T. Ferreira Departamento de Bioquimica Medica Universidade Federal do Rio de Janeiro Brazil The structures and stabilities of recombinant chicken muscle troponin I TnI and T TnT were investigated by a combination of bis-ANS binding and equilibrium unfolding studies. Uniike mott folded proteins isolated Till and TnT bind the hydrophobic fluorescent probe bis-ANS indicating the existence of solvent-exposed hydrophobic domains in their structures. Bis-ANS bindmg to binai y or eien i y mixtures of Tnl TnT and troponin C TnC in solution is significantly lower than binding to the isolated subunits which can be explained by burial of previously exposed hydrophobic domains upon association of the subunits to form the native troponin complex. Equiiibrium infolding ttudies oaf TnT and TnI by guanidine hydrochloride and urea monitored by changes in far-UV CD and bis-ANS fluorescence revealed noncooperative folding transitions for both proteins and the existence of partially folded intermediate states. Taken together these results indicate that isolated TnI and TnT are partially unstructured proteins and suggest that conformational plasticity of the isolated subunits may play an important role in macromolecular recognition for the assembly of the troponin complex. Keywords troponin I troponin T urea guanidine hydrochloride circular dichroism. It is generally assumed that proteins must be fully folded in order to carry out their biological functions. In otther words. biological activity and specificity are thought to be directly connected to a high degree of geometrical precision. However recent studies call into question whether or not all functional proteins within the cell have stable secondary and tertiary structures 1 2 . Disorder in protein ttnlciutes can be global or .

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