Recent Insights in Islet Amyloid Polypeptide-Induced Membrane Disruption and Its Role in β-Cell Death in Type 2 Diabetes Mellitus

The presence of fibrillar protein deposits (amyloid) of human islet amyloid polypeptide (hIAPP) in the pancreatic islets of Langerhans is thought to be related to death of the insulin-producing islet β-cells in type 2 diabetes mellitus (DM2). The mechanism of hIAPP-induced β-cell death is not understood. However, there is growing evidence that hIAPP-induced disruption of β-cell membranes is the cause of hIAPP cytotoxicity. Amyloid cytotoxicity by membrane damage has not only been suggested for hIAPP, but also for peptides and proteins related to other misfolding diseases, like Alzheimer's disease, Parkinson's disease, and prion diseases. Here we review the interaction of hIAPP with membranes, and discuss recent progress in the field, with a focus on hIAPP structure and on the proposed mechanisms of hIAPP-induced membrane damage in relation to β-cell death in DM2

Designed glycopeptidomimetics disrupt protein−protein interactions mediating amyloid β‑peptide aggregation and restore neuroblastoma cell viability

How anti-Alzheimer’s drug candidates that reduce amyloid 1−42 peptide fibrillization interact with the most neurotoxic species is far from being understood. We report herein the capacity of sugar-based peptidomimetics to inhibit both Aβ1−42 early oligomerization and fibrillization. A wide range of bio- and physicochemical techniques, such as a new capillary electrophoresis method, nuclear magnetic resonance, and surface plasmon resonance, were used to identify how these new molecules can delay the aggregation of Aβ1−42. We demonstrate that these molecules interact with soluble oligomers in order to maintain the presence of nontoxic monomers and to prevent fibrillization. These compounds totally suppress the toxicity of Aβ1−42 toward SH-SY5Y neuroblastoma cells, even at substoichiometric concentrations. Furthermore, demonstration that the best molecule combines hydrophobic moieties, hydrogen bond donors and acceptors, ammonium groups, and a hydrophilic β-sheet breaker element provides valuable insight for the future structure-based design of inhibitors of Aβ1−42 aggregation

The role of the disulfide bond in the interaction of islet amyloid polypeptide with membranes

Human islet amyloid polypeptide (hIAPP) forms amyloid fibrils in pancreatic islets of patients with type 2 diabetes mellitus. It has been suggested that the N-terminal part, which contains a conserved intramolecular disulfide bond between residues 2 and 7, interacts with membranes, ultimately leading to membrane damage and β-cell death. Here, we used variants of the hIAPP1–19 fragment and model membranes of phosphatidylcholine and phosphatidylserine (7:3, molar ratio) to examine the role of this disulfide in membrane interactions. We found that the disulfide bond has a minor effect on membrane insertion properties and peptide conformational behavior, as studied by monolayer techniques, 2H NMR, ThT-fluorescence, membrane leakage, and CD spectroscopy. The results suggest that the disulfide bond does not play a significant role in hIAPP–membrane interactions. Hence, the fact that this bond is conserved is most likely related exclusively to the biological activity of IAPP as a hormone

Biophysical investigation of the membrane-disrupting mechanism of the antimicrobial and amyloid-like peptide dermaseptin S9.

Dermaseptin S9 (Drs S9) is an atypical cationic antimicrobial peptide with a long hydrophobic core and with a propensity to form amyloid-like fibrils. Here we investigated its membrane interaction using a variety of biophysical techniques. Rather surprisingly, we found that Drs S9 induces efficient permeabilisation in zwitterionic phosphatidylcholine (PC) vesicles, but not in anionic phosphatidylglycerol (PG) vesicles. We also found that the peptide inserts more efficiently in PC than in PG monolayers. Therefore, electrostatic interactions between the cationic Drs S9 and anionic membranes cannot explain the selectivity of the peptide towards bacterial membranes. CD spectroscopy, electron microscopy and ThT fluorescence experiments showed that the peptide adopts slightly more β-sheet and has a higher tendency to form amyloid-like fibrils in the presence of PC membranes as compared to PG membranes. Thus, induction of leakage may be related to peptide aggregation. The use of a pre-incorporation protocol to reduce peptide/peptide interactions characteristic of aggregates in solution resulted in more α-helix formation and a more pronounced effect on the cooperativity of the gel-fluid lipid phase transition in all lipid systems tested. Calorimetric data together with (2)H- and (31)P-NMR experiments indicated that the peptide has a significant impact on the dynamic organization of lipid bilayers, albeit slightly less for zwitterionic than for anionic membranes. Taken together, our data suggest that in particular in membranes of zwitterionic lipids the peptide binds in an aggregated state resulting in membrane leakage. We propose that also the antimicrobial activity of Drs S9 may be a result of binding of the peptide in an aggregated state, but that specific binding and aggregation to bacterial membranes is regulated not by anionic lipids but by as yet unknown factors

Residue specific effects of human islet polypeptide amyloid on self-assembly and on cell toxicity

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CD spectra (190–270 nm) of Drs S9 (25 µM) in (A) phosphate buffer at pH 7.4, (B) DOPC LUVs, (C) DOPC/DOPG 7∶3 LUVs, and (D) DOPG LUVS.

<p>Peptide was either added (solid line) or incorporated (dashed line) to vesicles. Peptide/lipid ratio was 1∶20.</p

Functionalised tetraarylstannanes Sn[C6H4-R]4 (R=–CH(CH2O)2, –CHO, –COOH, –CHN–NH–C6H3-2,4-(NO2)2, –CH2OH, –CO–NH–CH2–COO–CH3, –CH[N(C2H4)2O]2)

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³¹P-NMR spectra of multilamellar vesicles composed of (A) POPC-d₃₁, (B) POPC-d₃₁/POPG 7∶3 and (C) POPG-d₃₁.

<p>²H NMR spectra of multilamellar vesicles composed of (D) POPC-d₃₁, (E) POPC-d₃₁/POPG 7∶3 and (F) POPG-d₃₁. Experiments were performed in the absence (top) and in the presence (bottom) of Drs S9. Vertical dashed lines are eye guides for lipid ordering at plateau positions.</p

Order parameter profile calculated for de-Paked spectra of (A) POPC-d₃₁, (B) POPC-d₃₁/POPG 7∶3, and (C) POPG-d₃₁, in the absence (diamond) and in the presence (cross) of Drs S9.

<p>Order parameter profile calculated for de-Paked spectra of (A) POPC-d₃₁, (B) POPC-d₃₁/POPG 7∶3, and (C) POPG-d₃₁, in the absence (diamond) and in the presence (cross) of Drs S9.</p