NFGAIL Amyloid Oligomers: The Onset of Beta-Sheet Formation and the Mechanism for Fibril Formation
Hoffmann, W.; Folmert, K.; Moschner, J.; Xing, H.; von Berlepsch, H.; Koksch, B.; Bowers, M. T.; von Helden, G.; Pagel, K.* – 2018
The hexapeptide NFGAIL is a highly amyloidogenic peptide, derived from the human islet amyloid polypeptide (hIAPP). Recent investigations indicate that presumably soluble hIAPP oligomers are one of the cytotoxic species in type II diabe-tes. Here we use Thioflavin T staining, transmission electron microscopy as well as ion mobility-mass spectrometry coupled to infrared (IR) spectroscopy to study the amyloid formation mechanism and the quaternary- and secondary-structure of soluble NFGAIL oligomers. Our data reveal that at neutral pH NFGAIL follows a nucleation-dependent mechanism to form amyloid fibrils. During the lag phase, highly polydisperse, polymorph, and compact oligomers (oligomer number n=2-13) as well as extended intermediates (n=4-11) are present. IR secondary structural analysis reveals that compact conformations adopt turn-like structures, whereas extended oligomers exhibit a significant amount of β-sheet content. This agrees well with previous molecular dynamic simulations and provides direct experimental evidence that unordered off-pathway NFGAIL aggregates up to the size of at least the 13-mer as well as partially folded β-sheet containing oligomers are coexisting.