Amyloid 尾42 self-assembly is complex,
with multiple path
ways leading to large insoluble fibrils or soluble oligomers. Oligomers are no
w regarded as most germane to Alzheimer鈥檚 pathogenesis. We have investigated the hypothesis that oligomer formation itself occurs through alternative path
ways,
with some leading to synapse-binding toxins. Immediately after adding synthetic peptide to buffer, solutions of A尾42
were separated by a 50 kDa filter and fractions assessed by SDS-
PAGE silver stain, Western blot, immunoprecipitation, and capacity for synaptic binding. A尾42 rapidly assembled into aqueous-stable oligomers,
with similar protein abundance in small (<50 kDa) and large (>50 kDa) oligomer fractions. Initially, both fractions
were SDS-labile and resolved into tetramers, trimers, and monomers by SDS-PAGE. Upon continued incubation, the larger oligomers developed a small population of SDS-stable 10鈥?6mers, and the smaller oligomers generated gel-impermeant complexes. The t
wo fractions associated differently
with neurons,
with prominent synaptic binding limited to larger oligomers. Even
within the family of larger oligomers, synaptic binding
was associated
with only a subset of these species, as a ne
w scFv antibody (NUsc1) immunoprecipitated only a small portion of the oligomers
while eliminating synaptic binding. Interestingly, lo
w doses of the peptide KLVFFA blocked assembly of the 10鈥?6mers, and this result
was associated
with loss of the smaller clusters of oligomers observed at synaptic sites. What distinguishes these smaller clusters from the unaffected larger clusters is not yet kno
wn. Results indicate that distinct species of A尾 oligomers are generated by alternative assembly path
ways and that synapse-binding subpopulations of A尾 oligomers could be specifically targeted for Alzheimer鈥檚 therapeutics.
Keywords:
Alzheimer鈥檚 disease; amyloid beta; blocking peptide; therapeutics; single-chain variable fragment antibody; oligomerization