Molecular Motions and Interactions in Aqueous Solutions of Thymosin-β 4 , Stabilin CTD and Their 1 : 1 Complex, Studied by 1 H-NMR Spectroscopy.

Wide-line ¹ H NMR measurements were extended and all results were interpreted in a thermodynamics-based new approach on aqueous solutions of thymosin-β ₄ (Tβ ₄ ), stabilin cytoplasmic domain (CTD), and their 1 : 1 complex. Energy distributions of potential barriers controlling the motion of protein-bound water molecules were determined. Heterogeneous and homogeneous regions were found in the protein-water interface. The measure of heterogeneity of this interface gives quantitative value for the portion of disordered parts in the protein. Ordered structural elements were found extending up to ∼20 % of the individual whole proteins. About 40 % of the binding sites of free Tβ ₄ get involved in bonds holding the complex together. The complex has the most heterogeneous solvent accessible surface (SAS) in terms of protein-water interactions. The complex is more disordered than Tβ ₄ or stabilin CTD. The greater SAS area of the complex is interpreted as a clear sign of its open structure.
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