Structural Characterisation of Islet Amyloid Polypeptide Fibrils

139

125

In type-2 diabetes (T2D) and Parkinson's disease (PD), polypeptide assembly into amyloid fibers plays central roles: in PD, α-synuclein (aS) forms amyloids and in T2D, amylin [islet amyloid polypeptide (IAPP)] forms amyloids. Using a combination of biophysical methods in vitro we have investigated whether aS, IAPP, and unprocessed IAPP, pro-IAPP, polypeptides can cross-react. Whereas IAPP forms amyloids within minutes, aS takes many hours to assemble into amyloids and pro-IAPP aggregates even slower under the same conditions. We discovered that preformed amyloids of pro-IAPP inhibit, whereas IAPP amyloids promote, aS amyloid formation. Amyloids of aS promote pro-IAPP amyloid formation, whereas they inhibit IAPP amyloid formation. In contrast, mixing of IAPP and aS monomers results in coaggregation that is faster than either protein alone; moreover, pro-IAPP can incorporate aS monomers into its amyloid fibers. From this intricate network of cross-reactivity, it is clear that the presence of IAPP can accelerate aS amyloid formation. This observation may explain why T2D patients are susceptible to developing PD.α-synuclein | fluorescence | amyloid | atomic force microscopy | amylin

Section: Resultsmentioning

confidence: 99%

Cross-talk between amyloidogenic proteins in type-2 diabetes and Parkinson’s disease

Horváth

Wittung-Stafshede

2016

139

125

“…The convective flow-induced nanofibrillar alignment in the drying residue resulted in diffraction patterns with fibrous texture (21) revealing a cross-β pattern (Fig. 2B) (22)(23)(24). The azimuthally averaged intensity profiles of the meridian and equator are shown in Fig.…”

Section: Resultsmentioning

confidence: 99%

Aliphatic peptides show similar self-assembly to amyloid core sequences, challenging the importance of aromatic interactions in amyloidosis

Lakshmanan

Cheong

Accardo

et al. 2012

124

148

The self-assembly of abnormally folded proteins into amyloid fibrils is a hallmark of many debilitating diseases, from Alzheimer's and Parkinson diseases to prion-related disorders and diabetes type II. However, the fundamental mechanism of amyloid aggregation remains poorly understood. Core sequences of four to seven amino acids within natural amyloid proteins that form toxic fibrils have been used to study amyloidogenesis. We recently reported a class of systematically designed ultrasmall peptides that self-assemble in water into cross-β-type fibers. Here we compare the self-assembly of these peptides with natural core sequences. These include core segments from Alzheimer's amyloid-β, human amylin, and calcitonin. We analyzed the self-assembly process using circular dichroism, electron microscopy, X-ray diffraction, rheology, and molecular dynamics simulations. We found that the designed aliphatic peptides exhibited a similar self-assembly mechanism to several natural sequences, with formation of α-helical intermediates being a common feature. Interestingly, the self-assembly of a second core sequence from amyloid-β, containing the diphenylalanine motif, was distinctly different from all other examined sequences. The diphenylalanine-containing sequence formed β-sheet aggregates without going through the α-helical intermediate step, giving a unique fiberdiffraction pattern and simulation structure. Based on these results, we propose a simplified aliphatic model system to study amyloidosis. Our results provide vital insight into the nature of early intermediates formed and suggest that aromatic interactions are not as important in amyloid formation as previously postulated. This information is necessary for developing therapeutic drugs that inhibit and control amyloid formation.

“…3b). In both cases, hIAPP forms straight, unbranched fibrils with a width of 10-15 nm and a length of 0.5-1 m, characteristic of hIAPP amyloid fibrils (33,34). An additional interesting feature in the micrographs is that most of the LUVs that are in contact with hIAPP fibrils show distorted, noncircular shapes (asterisks in Fig.…”

Section: Individual Hiapp Fibrils Are Associated With Distorted Phospmentioning

confidence: 98%

Membrane damage by human islet amyloid polypeptide through fibril growth at the membrane

Engel

Khemtémourian²,

Kleijer³

et al. 2008

437

482

Fibrillar protein deposits (amyloid) in the pancreatic islets of Langerhans are thought to be involved in death of the insulinproducing islet ␤ cells in type 2 diabetes mellitus. It has been suggested that the mechanism of this ␤ cell death involves membrane disruption by human islet amyloid polypeptide (hIAPP), the major constituent of islet amyloid. However, the molecular mechanism of hIAPP-induced membrane disruption is not known. Here, we propose a hypothesis that growth of hIAPP fibrils at the membrane causes membrane damage. We studied the kinetics of hIAPP-induced membrane damage in relation to hIAPP fibril growth and found that the kinetic profile of hIAPP-induced membrane damage is characterized by a lag phase and a sigmoidal transition, which matches the kinetic profile of hIAPP fibril growth. The observation that seeding accelerates membrane damage supports the hypothesis. In addition, variables that are well known to affect hIAPP fibril formation, i.e., the presence of a fibril formation inhibitor, hIAPP concentration, and lipid composition, were found to have the same effect on hIAPP-induced membrane damage. Furthermore, electron microscopy analysis showed that hIAPP fibrils line the surface of distorted phospholipid vesicles, in agreement with the notion that hIAPP fibril growth at the membrane and membrane damage are physically connected. Together, these observations point toward a mechanism in which growth of hIAPP fibrils, rather than a particular hIAPP species, is responsible for the observed membrane damage. This hypothesis provides an additional mechanism next to the previously proposed role of oligomers as the main cytotoxic species of amyloidogenic proteins.amylin ͉ amyloid cytotoxicity ͉ large unilamellar vesicles ͉ protein-membrane interaction ͉ type 2 diabetes mellitus T ype 2 diabetes mellitus (DM2) is characterized histopathologically by the presence of fibrillar amyloid deposits in the pancreatic islets of Langerhans. Amyloid cytotoxicity is thought to be an early mechanism involved in death of insulin-producing islet ␤ cells in DM2 (1). The main component of islet amyloid, and the actual fibril-forming molecule, is a 37-amino acid peptide called human islet amyloid polypeptide (hIAPP) or amylin, which is produced together with insulin in the pancreatic islet ␤-cells. It is thought that ␤ cells of DM2 patients are somehow killed through hIAPP-induced damage of the ␤ cell membrane (2). However, our knowledge of the mechanism of hIAPP-induced membrane damage is extremely sparse. It is not known how cytotoxic hIAPP species interact with cellular membranes and induce cell death. Furthermore, it is not established whether cytotoxic hIAPP species are formed before contacting the membrane or whether a membrane environment is in fact required for the formation of cytotoxic hIAPP species.The prevailing view is that membrane damage and concomitant ␤ cell death are caused by cytotoxic hIAPP oligomers (2-9). There are indications that these oligomers form ion channels (2, 3), as has been suggeste...