Molecular motions and interactions in aqueous solutions of thymosin-β4, stabilin CTD and their 1:1 complex, studied by 1H-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 C-terminal 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.