A dumb-bell shaped global structure with 4 EF hands and active Ca2+-binding sites in both the N- and C-termini is critical for anchoring in the fiber and regulating muscular contraction.
The dumb-bell shaped global structure of regulatory proteins with 4 EF hands is critical for the Ca2+-switch mechanism in muscular contraction.
To determine the significance of the global structure of the regulatory proteins in the mechanism of the Ca2+-switch in cardiac and skeletal muscle contractions, the properties of a family of Ca2+-binding proteins with 4 or 3 EF-hand motifs have been studied with desensitized skinned fiber preparations. Proteins with 4 EF hands (such as troponins C - TnCs) are dumb-bell shaped, those with 3 EF hands (parvalbumin) being ellipsoidal. The number of active sites varied between four and two. We find that the ability to anchor in the fiber is limited to proteins with 4 EF hands and, at least, two active Ca2+-binding sites, one each in the N- and C-termini. The results suggest that the dumb-bell shaped global structure is critical for the switching action in muscular contraction, and a trigger site in the N-terminus and a structural site in the C-terminus need to be active in order to regulate contractility.
Babu et al. (Mon,) conducted a other in Cardiac and skeletal muscle contractions. Ca2+-binding proteins with 4 or 3 EF-hand motifs was evaluated on Ability to anchor in the fiber and regulate contractility. A dumb-bell shaped global structure with 4 EF hands and active Ca2+-binding sites in both the N- and C-termini is critical for anchoring in the fiber and regulating muscular contraction.
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