Size Determination of Protein Oligomers/Aggregates Using Diffusion NMR Spectroscopy.

Diffusion-ordered spectroscopy (DOSY) is a widely used NMR technique for the identification of different chemical moieties/compounds contained in mixtures and has been successfully employed for the separation of small molecules based on hydrodynamic radii. Herein we show that DOSY can also be applied for the size determination of larger biomolecules such as proteins and protein oligomers/aggregates. Proof-of-principle is first shown with a cross-linked oligomeric protein mixture where the hydrodynamic volumes of each component are estimated and subsequently verified with size-exclusion HPLC and SDS polyacrylamide gel electrophoresis. We then determine the sizes of protein oligomers contained in a protein solution subjected under amyloid fibrillogenesis conditions. These studies aim to provide insight into the kinetics behind protein aggregation involved in amyloidosis as well as to determine the hydrodynamic radii of proteins within the mixture.