Structures of Rat and Human Islet Amyloid Polypeptide IAPP₁₋₁₉ in Micelles by NMR Spectroscopy

Abstract

Disruption of the cellular membrane by the amyloidogenic peptide IAPP (or amylin) has been implicated in β-cell death during type 2 diabetes. While the structure of the mostly inert fibrillar form of IAPP has been investigated, the structural details of the highly toxic prefibrillar membrane-bound states of IAPP have been elusive. A recent study showed that a fragment of IAPP (residues 1-19) induces membrane disruption to a similar extent as the full-length peptide. However, unlike the fulllength IAPP peptide, IAPP 1-19 is conformationally stable in an α-helical conformation when bound to the membrane. In vivo and in vitro measurements of membrane disruption indicate the rat version of IAPP [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] , despite differing from hIAPP [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] by the single substitution of Arg18 for His18, is significantly less toxic than hIAPP [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] , in agreement with the low toxicity of the full-length rat IAPP peptide. To investigate the origin of this difference at the atomic level, we have solved the structures of the human and rat IAPP [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] peptides in DPC micelles. While both rat and human IAPP [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] fold into similar mostly α-helical structures in micelles, paramagnetic quenching NMR experiments indicate a significant difference in the membrane orientation of hIAPP [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] and rIAPP [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] . At pH 7.3, the more toxic hIAPP [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] peptide is buried deeper within the micelle, while the less toxic rIAPP [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] peptide is located at the surface of the micelle. Deprotonating H18 in hIAPP [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] reorients the peptide to the surface of the micelle. This change in orientation is in agreement with the significantly reduced ability of hIAPP [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] to cause membrane disruption at pH 6.0. This difference in peptide topology in the membrane may correspond to similar topology differences for the fulllength human and rat IAPP peptides, with the toxic human IAPP peptide adopting a transmembrane orientation and the nontoxic rat IAPP peptide bound to the surface of the membrane.Islet amyloid polypeptide (IAPP, 1 also known as amylin) is one of an increasing number of proteins in which the propensity to form a misfolded state is correlated with pathologies in tissue functioning. Physiologically, IAPP is one of a family of peptides related to calcitonin that act in the control of metabolic functions. Specifically, IAPP acts in concert with insulin to control plasma glucose levels...

Dynamic α-Helix Structure of Micelle-bound Human Amylin

“…A very recent NMR structure of a 1-19-residue fragment of human amylin in dodecylphosphocholine micelles identified ␣-helix structure between residues 7 and 17 (18). The difference from our structure at the C terminus is probably due to end fraying effects in the fragment.…”

Islet amyloid polypeptide toxicity and membrane interactions

“…The importance of postion-18 is consistent with NMR studies of IAPP fragments in the presence of model membranes (45). hIAPP [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] and rIAPP [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] , which differ only in the identity of residue-18, bind membranes in different orientations, and these differences are believed to correlate with the difference in the potential for membrane disruption (45,46). In summary, our data dissociate IAPP-induced leakage of standard model membranes from direct cellular toxicity, thereby indicating that further studies to identify the precise mechanism (s) of IAPP cellular toxicity are essential for the optimal development of therapeutic strategies to prevent T2D and islet graft failure.…”

Ganglioside‐induced amyloid formation by human islet amyloid polypeptide in lipid rafts

“…The C-terminal domain has amyloidogenic property, and the N-terminal fragment of hIAPP was alone sufficient to induce membrane perturbation and a single mutation abolished the activity [31][32][33]. The interaction of the N-terminal part of hIAPP with membranes is driven by electrostatic interactions.…”