The Dispersion of Water Proton Spin-Lattice Relaxation Rates in Aqueous Human Protein HC (α 1-Microglobulin) Solutions

The 1H NMR Fast Field Cycling relaxometry was applied to study the molecular dynamics of the human protein HC (α1-microglobulin), its hydration and aggregation in solution state. The 1H NMRD data have revealed the complex nature of the water/protein HC system resulting from the co-existence of monomer and dimer forms of the protein in solution as well as the presence of oligosaccharides linked to the polypeptide chain. A comparison of the average correlation time values <ζc> obtained from the model-free fits with the values predicted on the basis of hydrodynamic ζr theory, suggests that the dynamics in solution state is governed mainly by the dimer form of the protein HC (the dominant contribution to the water proton-spin lattice relaxation comes from exchanging protons from the surface of the dimer). The existence of small number of oligomeric forms of the protein HC in solutions is postulated because of the two-step shape of water proton spin-lattice relaxation rate dispersion profiles.