Three-Dimensional Structure and Orientation of Rat Islet Amyloid Polypeptide Protein in a Membrane Environment by Solution NMR Spectroscopy

Abstract

Islet amyloid polypeptide (IAPP or amylin) is a 37-residue peptide hormone associated with glucose metabolism that is cosecreted with insulin by β-cells in the pancreas. Since human IAPP is a highly amyloidogenic peptide, it has been suggested that the formation of IAPP amyloid fibers is responsible for the death of β-cells during the early stages of type II diabetes. It has been hypothesized that transient membrane-bound α-helical structures of human IAPP are precursors to the formation of these amyloid deposits. On the other hand, rat IAPP forms transient α-helical structures but does not progress further to form amyloid fibrils. To understand the nature of this intermediate state and the difference in toxicity between the rat and human versions of IAPP, we have solved the high-resolution structure of rat IAPP in the membrane-mimicking detergent micelles composed of dodecylphosphocholine. The structure is characterized by a helical region spanning the residues A5 to S23 and a disordered C-terminus. A distortion in the helix is seen at R18 and S19 that may be involved in receptor binding. Paramagnetic quenching NMR experiments indicate that rat IAPP is bound on the surface of the micelle, in agreement with other nontoxic forms of IAPP. A comparison to the detergent-bound structures of other IAPP variants indicates that the N-terminal region may play a crucial role in the self-association and toxicity of IAPP by controlling access to the putative dimerization interface on the hydrophobic face of the amphipathic helix.

Beta structure motifs of islet amyloid polypeptides identified through surface-mediated assemblies

“…The solution NMR spectroscopy results about rIAPP structures (39) could be a corroborative evidence for the current STM experiments on the key sites of rIAPP beta-like motif. In the model described by Nanga et al (39), the structure of rIAPP is composed of an ordered helix (rIAPP [5][6][7][8][9][10][11][12][13][14][15][16][17] ), a more disordered helix (rIAPP [20][21][22][23] ), and an unstructured segment (rIAPP [24][25][26][27][28][29][30][31][32][33][34][35][36][37] ), which is qualitatively consistent with the two possible sites around Ser 19 , and Leu 23 obtained from the STM experiments. The polydispersity of the rIAPP 8-37 betalike motif could be associated with its less fibrillogenic characteristics.…”

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.…”

Clustering and Internalization of Toxic Amylin Oligomers in Pancreatic Cells Require Plasma Membrane Cholesterol

“…Despite this, the role of membrane composition in amylin assembly and aggregation at the membrane interfaces has not been investigated until very recently (33-35, 38, 39). The N-terminal region and His-18 play crucial roles in the self-assembly and interactions of human amylin with membranes (24,40). Concomitant with these structural studies, biochemical studies identify membranes as a potent determinant of amylin aggregation in vitro (33,38,(41)(42)(43).…”