Probing the Nucleus Model for Oligomer Formation during Insulin Amyloid Fibrillogenesis

• Published in: Biophysical journal 2010-12, Vol.99 (12), p.3979-3985
• Main Authors: Pease, Leonard F., Sorci, Mirco, Guha, Suvajyoti, Tsai, De-Hao, Zachariah, Michael R., Tarlov, Michael J., Belfort, Georges
• Format: Article
• Language: English
• Subjects: Alzheimer's disease; Amyloid - chemistry; Chemical compounds; Databases, Protein; Fibers; Insulin; Insulin - chemistry; Membranes; Models, Biological; Models, Molecular; Monomers; Nanocomposites; Nanomaterials; Nanostructure; Neutrons; Oligomers; Protein; Protein Structure, Quaternary; Size distribution; Time Factors
• ISSN: 0006-3495; 1542-0086
• DOI: 10.1016/j.bpj.2010.10.010

We find evidence for a direct transition of insulin monomers into amyloid fibrils without measurable concentrations of oligomers or protofibrils, suggesting that fibrillogenesis may occur directly from assembly of denaturing insulin monomers rather than by successive transitions through protofibril nuclei. To support our finding, we obtain size distributions using electrospray differential mobility analysis (ES-DMA), which provides excellent resolution to clearly distinguish among small oligomers and rapidly generates statistically significant size distributions. The distributions detect an absence of significant peaks between 6 nm and 17 nm as the monomer reacts into fibers—exactly the size range observed by others for small-angle-neutron-scattering-measured intermediates and for circular supramolecular structures. They report concentrations in the nanomolar range, whereas our limit of detection remains three-orders-of-magnitude lower (