Oligomers are commonly observed intermediates at the initial stages of amyloid fibril formation. They are toxic to neurons and cause decrease in neural transmission and long-term potentiation. We describe an in vitro study of the initial steps in amyloid fibril formation by human stefin B, which proved to be a good model system. Due to relative stability of the initial oligomers of stefin B, electrospray ionization mass spectrometry (ESI MS) could be applied in addition to size exclusion chromatography (SEC). These two techniques enabled us to separate and detect distinguished oligomers from the monomers: dimers, trimers, tetramers, up to decamers. The amyloid fibril formation process was followed at different pH and temperatures, including such conditions where the process was slow enough to detect the initial oligomeric species at the very beginning of the lag phase and those at the end of the lag phase. Taking into account the results of the lower-order oligomers transformations early in the process, we were able to propose an improved model for the stefin B fibril formation.

Amyloid β-protein (Aβ) assembles into oligomers that play a seminal role in Alzheimer's disease (AD), a leading cause of dementia among the elderly. Despite undisputed importance of Aβ oligomers, their structure and the basis of their toxicity remain elusive. Previous experimental studies revealed that the [K16A] substitution strongly inhibits toxicity of the two predominant Aβ alloforms in the brain, Aβ 40 [K16A] substitution induces formation of more compact oligomers than the [K28A] substitution. If the structure-function paradigm applies to Aβ oligomers, then the observed substitution-specific structural changes in Aβ 40 and Aβ 42 oligomers are critical for understanding the structural basis of Aβ oligomer toxicity and correct identification of therapeutic targets against AD.

Assembly of an amyloidogenic protein stefin B into molten globule oligomers is studied by efficient discrete molecular dynamics. Consistent with in vitro findings, tetramers form primarily through dimer association, resulting in a decreased trimer abundance. Oligomers up to heptamers display elongated rod-like morphologies akin to protofibrils, whereas larger oligomers, decamers through dodecamers, form elongated, branched, as well as annular structures, providing structural insights into pore forming ability and toxicity of amyloidogenic proteins.