From Peptide Fragments to Whole Protein: Copper(II) Load and Coordination Features of IAPP

Abstract

The copper-binding features of rat islet amyloid polypeptide (r-IAPP) are herein disclosed through the determination of the stability constants and spectroscopic properties of its copper complex species. To mimic the metal binding sites of the human IAPP (h-IAPP), a soluble, single-point mutated variant of r-IAPP, having a histidine residue in place of Arg18, was synthesized, that is, r-IAPP(1-37; R18H). The peptide IAPP(1-8) was also characterized to have deeper insight into the N-terminus copper(II)-binding features of r-IAPP as well as of its mutated form. A combined experimental (thermodynamic and spectroscopic) and computational approach allowed us to assess the metal loading and the coordination features of the whole IAPP. At physiological pH, the N-terminal amino group is the Cu main binding site both of entire r-IAPP and of its mutated form that mimics h-IAPP. The histidine residue present in this mutated polypeptide accounts for the second Cu binding. We can speculate that the copper driven toxicity of h-IAPP in comparison to that of r-IAPP can be attributed to the different metal loading and the presence of a second metal anchoring site, the His , whose role is usually invoked in the process of h-IAPP aggregation.

Zinc Interactions with a Soluble Mutated Rat Amylin to Mimic Whole Human Amylin: An Experimental and Simulation Approach to Understand Stoichiometry, Speciation and Coordination of the Metal Complexes

“…Furthermore, our results are in agreement with those obtained studying Zn 2 + -h-IAPP(1-37)s ystem by ESI-MS [43] and IMS-MS [72] suggesting that our mutated form of r-IAPP(1-37) (i.e -r-IAPP(1-37,R18 H)) is ar eliable model to investigate the interaction of Zn 2 + with the h-IAPP(1-37) as previously found for copper(II) ion. [64] Moreover,E SI-MS experiments have been performed by the titration of 10 mm h-IAPP(1-37) from 1t o5 000 mm ZnCl 2 and a binuclear species found at mm zinc concentrations. [43] The high resolution (HR) ESI-MS measurements carriedo ut by us at 10 mm of r-IAPP(1-37;R18 H) and at highm etal to ligand ratios (Figure 2, red box) revealavery low intensity m/z signal ( Figure 2) attributed to ad inuclearz inc complex.…”

His18 promotes reactive oxidative stress production in copper-ion mediated human islet amyloid polypeptide aggregation

“…All synthetic human and rat IAPP/amylin fragments (hIAPP (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11), hIAPP (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28), hIAPP (28)(29)(30)(31)(32)(33)(34)(35)(36)(37), and rIAPP (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)…”

“…6,7 hIAPP (also named as amylin) is a peptide hormone that is initially produced by b-cells of the islet of the pancreas. It is 37 residues in length and has different functional domains including an N terminus, C terminus and the amyloidogenic central peptide sequence (residues 20-29), [8][9][10] which are prone to forming brils. The aggregation process of hIAPP has been proved to be modulated by many factors including pH value, metal ions, small chemical molecules, etc.…”

“…hIAPP (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28) fragment was used as a main model, as it contains the region (20)(21)(22)(23)(24)(25)(26)(27)(28) for amyloid formation as well as the main binding site (His18) for the metal ions. 10,13,29 We rst compared the amount of H 2 O 2 production in several fragments co-incubated with copper ions including hIAPP (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11), hIAPP (11)(12)(13)(14)(15)(16)(17)(18)(19)…”

Aggregation of biologically important peptides and proteins: inhibition or acceleration depending on protein and metal ion concentrations

“…Other studies report that Cu 2+ binds to amylin at the imidazole ring of His18 (ref. 54) and to the three preceding amides at the N-terminal side of His18 (ref. 52) and at Lys1.…”