Structural differences in Abeta amyloid protofibrils and fibrils mapped by hydrogen exchange--mass spectrometry with on-line proteolytic fragmentation.
We report here structural differences between Abeta(1-40) protofibrils and mature amyloid fibrils associated with Alzheimer's disease as determined using hydrogen-deuterium exchange-mass spectrometry (HX-MS) coupled with on-line proteolysis. Specifically, we have identified regions of the Abeta(1-40) peptide containing backbone amide hydrogen atoms that are protected from HX or exposed when this peptide is incorporated into protofibrils or amyloid fibrils formed in phosphate-buffered saline without stirring at 37 degrees C. Study of protofibrils was facilitated by use of the protofibril-stabilizing agent calmidazolium chloride. Our data clearly show that both the C-terminal segment 35-40 and the N-terminal segment 1-19 are highly exposed to HX in both fibrils and protofibrils. In contrast, the internal fragment 20-34 is highly protected from exchange in fibrils but much less so in protofibrils. The data suggest that the beta-sheet elements comprising the amyloid fibril are already present in protofibrils, but that they are expanded into some adjacent residues upon the formation of mature amyloid. The N-terminal approximately ten residues appear to be unstructured in both protofibrils and fibrils. The 20-30 segment of Abeta(1-40) is more ordered in fibrils than in protofibrils, suggesting that, if protofibrils are a mechanistic precursor of fibrils, the transition from protofibril to fibril involves substantial ordering of this region of the Abeta peptide.
Kheterpal
Indu
I
Graduate School of Medicine University of Tennessee, Knoxville, TN 37920, USA.
Chen
Maolian
M
Cook
Kelsey D
KD
Wetzel
Ronald
R
D000595:Amino Acid Sequence; D016229:Amyloid beta-Peptides / Q000138:chemical synthesis / Q000737:chemistry* / Q000378:metabolism; D006859:Hydrogen; D007093:Imidazoles / Q000378:metabolism; D008969:Molecular Sequence Data; D010434:Pepsin A / Q000378:metabolism; D010446:Peptide Fragments / Q000138:chemical synthesis / Q000737:chemistry* / Q000378:metabolism; D017433:Protein Structure, Secondary; D021241:Spectrometry, Mass, Electrospray Ionization
D016229:Amyloid beta-Peptides; D007093:Imidazoles; D010446:Peptide Fragments; C078592:amyloid beta-protein (1-40); C031938:calmidazolium; D006859:Hydrogen; D010434:Pepsin A