Yuxiang Mo

Small oligomers formed early along human islet amyloid polypeptide (hIAPP) aggregation is responsible for the cell death in Type II diabetes. The epigallocatechin gallate (EGCG), a green tea extract, was found to inhibit hIAPP fibrillation. However, the inhibition mechanism and the conformational distribution of the smallest hIAPP oligomer - dimer are mostly unknown. Herein, we performed extensive replica exchange molecular dynamic simulations on hIAPP dimer with and without EGCG molecules. Extended hIAPP dimer conformations, with a collision cross section value similar to that observed by ion mobility-mass spectrometry, were observed in our simulations. Notably, these dimers adopt a three-stranded antiparallel β-sheet and contain the previously reported β-hairpin amyloidogenic precursor. We find that EGCG binding strongly blocks both the inter-peptide hydrophobic and aromatic-stacking interactions responsible for inter-peptide β-sheet formation and intra-peptide interaction crucial for β-hairpin formation, thus abolishes the three-stranded β-sheet structures and leads to the formation of coil-rich conformations. Hydrophobic, aromatic-stacking, cation-π and hydrogen-bonding interactions jointly contribute to the EGCG-induced conformational shift. This study provides, on atomic level, the conformational ensemble of hIAPP dimer and the molecular mechanism by which EGCG inhibits hIAPP aggregation.

Fibrillar deposits formed by the aggregation of the human islet amyloid polypeptide (hIAPP) are the major pathological hallmark of type 2 diabetes mellitus (T2DM). Inhibiting the aggregation of hIAPP is considered the primary therapeutic strategy for the treatment of T2DM. Hydroxylated carbon nanoparticles have received great attention in impeding amyloid protein fibrillation owing to their reduced cytotoxicity compared to the pristine ones. In this study, we investigated the influence of hydroxylated single-walled carbon nanotubes (SWCNT-OHs) on the first step of hIAPP aggregation: dimerization by performing explicit solvent replica exchange molecular dynamics (REMD) simulations. Extensive REMD simulations demonstrate that SWCNT-OHs can dramatically inhibit interpeptide β-sheet formation and completely suppress the previously reported β-hairpin amyloidogenic precursor of hIAPP. On the basis of our simulation results, we proposed that SWCNT-OH can hinder hIAPP fibrillation. This was further confirmed by our systematic turbidity measurements, thioflavin T fluorescence, circular dichroism (CD), transmission electron microscope (TEM), and atomic force microscopy (AFM) experiments. Detailed analyses of hIAPP-SWCNT-OH interactions reveal that hydrogen bonding, van der Waals, and π-stacking interactions between hIAPP and SWCNT-OH significantly weaken the inter- and intrapeptide interactions that are crucial for β-sheet formation. Our collective computational and experimental data reveal not only the inhibitory effect but also the inhibitory mechanism of SWCNT-OH against hIAPP aggregation, thus providing new clues for the development of future drug candidates against T2DM.

The human islet amyloid polypeptide (hIAPP) or amylin is a 37-residue hormone found as amyloid deposits in pancreatic extracts of nearly all type 2 diabetes patients. The fragment 20-29 of sequence SNNFGAILSS (hIAPP20-29) has been shown to be responsible for the amyloidogenic propensities of the full length protein. Various polymorphic forms of hIAPP20-29 fibrils were described by using Fourier transform infrared (FTIR) and solid-state NMR experiments: unseeded hIAPP20-29 fibril with out-of-register antiparallel beta-strands, and two forms of seeded hIAPP20-29 fibril, with in-register antiparallel or in-register parallel beta-strands. As a first step toward understanding this polymorphism, we explore the equilibrium structures of the soluble hIAPP20-29 trimer, using multiple molecular dynamics (MD) simulations with the Optimized Potential for Efficient structure Prediction (OPEP) coarse-grained implicit solvent force field for a total length of 3.2 micros. Although, the trimer is found mainly random coil, consistent with the signal measured experimentally during the lag phase of hIAPP20-29 fibril formation, the central FGAIL residues have a relative high propensity to form interpeptide beta-sheets and antiparallel beta-strands are more probable than parallel beta-strands. One MD-predicted out-of-register antiparallel three-stranded beta-sheet matches exactly the FTIR-derived unseeded hIAPP20-29 fibril model. Our simulations, however, do not reveal any evidence of in-register parallel or in-register antiparallel beta-sheets as reported for seeded hIAPP20-29 fibrils. All these results indicate that fibril polymorphism is partially encoded in a trimer.

Fullerenols have garnered significant scientific interest in nano-technology and biomedicine. A detailed understanding of their interactions with proteins is fundamentally important for their biomedical applications. Human islet amyloid polypeptide (hIAPP) is an intrinsically disordered protein and its aggregation is associated with type 2 diabetes. Here, we investigated the nano-bio-interactions of fullerenol with hIAPP and focused on the effect of C60(OH)24 on hIAPP aggregation by replica-exchange molecular dynamic simulations. Our simulations show that isolated hIAPP dimers transiently populated amyloid-precursor (β-hairpin) containing β-sheet structure, whereas C60(OH)24 completely suppressed this fibril-prone structure, thus inhibiting hIAPP aggregation. The simulation-predicted inhibitory effect of fullerenols was validated by atom force microscopy and thioflavin T fluorescence experiments. We find C60(OH)24 binds to hIAPP via hydrogen bonding interactions with polar residues T9, Q10, N14, N21, N22, N31, N35 and T36 as well as the collective van der Waals and hydrogen-bonding interaction with Y37. Molecular dynamic simulations show that C60(OH)24 destabilized the hIAPP protofibril by mostly binding to the 20SNNFGAILSS29 amyloid core region. This study not only helps to understand the mechanisms involved in hIAPP aggregation and amyloid inhibition, but also provides new clues for the development of therapeutic candidates against type 2 diabetes.