Kinetic intermediates of amyloid fibrillation studied by hydrogen exchange methods with nuclear magnetic resonance

Amyloid fibrils with an ordered cross-β structure are one form of protein aberrant aggregates. Fibrils themselves and on-pathway small aggregates are involved in many neurodegenerative diseases and amylodoses. Over the past decade, much has been learned about the conformation of amyloid fibrils by using various biochemical and biophysical approaches. Amyloid fibrils accommodate rigid core structures composed of regular intra- and intermolecular non-covalent bonds such as hydrogen bonds, and disordered flexible regions exposed to solvents. In contrast to the improved understanding of fibril structures, few studies have investigated the short-living monomeric intermediates which interact with amyloid fibrils for elongation and the self-associated intermediates in the course of amyloidogenesis at the residue level. To study static fibrillar structures and kinetic intermediates, hydrogen/deuterium exchange (HDex) coupled with solution-state NMR spectroscopy is one of the most powerful methods with a high time and atomic resolution. Here, we review studies on the structural properties of amyloid fibrils based on a combination of dimethylsulfoxide-quenched HDex and NMR spectroscopy. Recent studies on transient kinetic intermediates during fibril growth by means of pulse-labeling HDex aided by a quenched-flow apparatus and NMR spectroscopy are focused on.

► Short-lived monomeric intermediates during fibril growth are still largely unknown.
► Pulse-labeling hydrogen exchange is useful for characterizing amyloid fibrillation.
► Kinetic intermediates of β2-m fibrillation were characterized at a residue level.
► Transient intermediates of β2-m monomers limited the kinetics of fibril elongation.
► A kinetic intermediate for fibril extension showed a largely unfolded conformation.