Amyloid formation under physiological conditions proceeds via a native-like folding intermediate.
Although most proteins can assemble into amyloid-like fibrils in vitro under extreme conditions, how proteins form amyloid fibrils in vivo remains unresolved. Identifying rare aggregation-prone species under physiologically relevant conditions and defining their structural properties is therefore an important challenge. By solving the folding mechanism of the naturally amyloidogenic protein beta-2-microglobulin at pH 7.0 and 37 degrees C and correlating the concentrations of different species with the rate of fibril elongation, we identify a specific folding intermediate, containing a non-native trans-proline isomer, as the direct precursor of fibril elongation. Structural analysis using NMR shows that this species is highly native-like but contains perturbation of the edge strands that normally protect beta-sandwich proteins from self-association. The results demonstrate that aggregation pathways can involve self-assembly of highly native-like folding intermediates, and have implications for the prevention of this, and other, amyloid disorders.
Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds LS2 9JT, UK.
Thomas R
TR
Jahn
Martin J
MJ
Parker
Steve W
SW
Homans
Sheena E
SE
Radford
D000596:Amino Acids / Q000737:chemistry; D000682:Amyloid / Q000737:chemistry* / Q000378:metabolism*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D009154:Mutation / Q000235:genetics; D019906:Nuclear Magnetic Resonance, Biomolecular; D011487:Protein Conformation; D017510:Protein Folding; D013696:Temperature; D013997:Time Factors; D001613:beta 2-Microglobulin / Q000737:chemistry* / Q000378:metabolism*
D000596:Amino Acids; D000682:Amyloid; D001613:beta 2-Microglobulin