Protein-Protein Connections-Oligomer, Amyloid and Protein Complex-By Wide Line 1 H NMR.

The amount of bonds between constituting parts of a protein aggregate were determined in wild type (WT) and A53T α-synuclein (αS) oligomers, amyloids and in the complex of thymosin-β ₄ -cytoplasmic domain of stabilin-2 (Tβ ₄ -stabilin CTD). A53T αS aggregates have more extensive βsheet contents reflected by constant regions at low potential barriers in difference (to monomers) melting diagrams ( MD s). Energies of the intermolecular interactions and of secondary structures bonds, formed during polymerization, fall into the 5.41 kJ mol ^-1 ≤ E _a ≤ 5.77 kJ mol ^-1 range for αS aggregates. Monomers lose more mobile hydration water while forming amyloids than oligomers. Part of the strong mobile hydration water-protein bonds break off and these bonding sites of the protein form intermolecular bonds in the aggregates. The new bonds connect the constituting proteins into aggregates. Amyloid-oligomer difference MD showed an overall more homogeneous solvent accessible surface of A53T αS amyloids. From the comparison of the nominal sum of the MD s of the constituting proteins to the measured MD of the Tβ ₄ -stabilin CTD complex, the number of intermolecular bonds connecting constituent proteins into complex is 20(1) H ₂ O/complex. The energies of these bonds are in the 5.40(3) kJ mol ^-1 ≤ E _a ≤ 5.70(5) kJ mol ^-1 range.