Solution state structures of human pancreatic amylin and pramlintide

Abstract

We have employed pramlintide (prAM) as a surrogate for hAM in CD and NMR studies of the conformational preferences of the N-terminal portion of the structure in media which do not provide long-lived monomeric solutions of hAM due to its rapid conversion to preamyloid beta aggregate states. Direct comparison of hAM and prAM could be made under helix-formation-favoring conditions. On the basis of CD and NMR studies: (i) the Cys(2)-Cys(7) loop conformation has a short-span of helix (Ala(5)-Cys(7)); (ii) the extent to which this helix propagates further into the sequence is medium-dependent; a helix from Ala(5) through Ser(20) (with end fraying from His(18) onward) is observed in aqueous fluoroalcohol media; (iii) in 12+ vol.% HFIP, the amyloidogenic region of hAM forms a second helical domain (Phe(23)-Ser(29)); (iv) the two helical regions of hAM do not have any specific geometric relationship as they are connected by a flexible loop that takes different conformations and (v) although the extreme C-terminus is essential for bioactivity, it is found to be extensively randomized with conformer interconversions occurring at a much faster rate than that is observed in the remainder of the peptide sequence. Two NMR-derived structures of the 1-22 sequence fragment of hAM have been derived. The work also serves to illustrate improved methods for the NMR characterization of helices. A detailed quantitative analysis of the NOE intensities observed in aqueous HFIP revealed alternative conformations in the C-terminal portion of the common amylin helix, a region that is known to be involved in the biorecognition phenomena leading to amyloidogenesis. Even though the SNN sequence appears to be a flexible loop, the chemical shifts (and changes induced upon helix structuring) suggest some interactions between the loop and the amyloidogenic segment of hAM that occur on partial helix formation.

Fibrillar dimer formation of islet amyloid polypeptides

“…18,[21][22][23][24][25][26][27][28][29] The full-length hIAPP monomer has been shown, both computationally and experimentally, to adopt various conformations, including unstructured coils, α-helices, long β-hairpins, and mixed α-helical and β-sheet conformations. [23][24][25][26][27][28][30][31][32][33][34] The interconversions among some of these conformations have also been characterized using advanced sampling techniques. 26,27 This complex folding behavior of the hIAPP monomer is also reflected in the multiple conformations observed for the mature fibrils, as discussed above.…”

Structure and Thermodynamics of Amylin Dimer Studied by Hamiltonian-Temperature Replica Exchange Molecular Dynamics Simulations

“…Brender et al, 7 for example, showed that membrane disruption and amyloid formation are two separate processes that happen in different regions of hIAPP. Liposome leakage experiments on full-length hIAPP and hIAPP [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] fragments at low concentration confirmed that the pathological membrane-disrupting activity comes from the IAPP N-terminal region as both sequences induce almost identical ABSTRACT: The loss of the insulin-producing β-cells in the pancreatic islets of Langerhans, responsible for type-II diabetes, is associated with islet amyloid deposits. The main component of these deposits is the amyloid fibrils formed by the 37-residue human islet amyloid polypeptide (hIAPP also known as amylin).…”

“…However, the peptide is exposed to the water, whereas hIAPP [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] is buried within the micelle. Interestingly, protonation of His18 of hIAPP [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] drives the peptide to the surface of the membrane and decreases its toxicity. 29,30 To better understand the role of the disulfide bridge and the amino acid sequence on the early stage of aggregation in solution, we study the full-length hIAPP dimer, with and without the disulfide bridge, and compare its conformational properties with that of the monomer, already studied by us, 20 as well as with rIAPP in both monomeric and dimeric forms.…”

Structure of micelle‐bound adrenomedullin: A first step toward the analysis of its interactions with receptors and small molecules

“…The knowledge of the three-dimensional structure of AM would be very useful to better understand the interactions of this peptide with its receptor and small molecule modulators and to develop new agonists and inhibitors. The structures for all other members of related peptides have been already solved, including PAMP, 19 CGRP, 20 amylin, 21 and calcitonin, 22 but no structural data was yet available for AM.…”