An Iridium(III) Complex as a Photoactivatable Tool for Oxidation of Amyloidogenic Peptides with Subsequent Modulation of Peptide Aggregation

Abstract

Aggregates of amyloidogenic peptides are involved in the pathogenesis of several degenerative disorders. Herein, an iridium(III) complex, Ir-1, is reported as a chemical tool for oxidizing amyloidogenic peptides upon photoactivation and subsequently modulating their aggregation pathways. Ir-1 was rationally designed based on multiple characteristics, including 1) photoproperties leading to excitation by low-energy radiation; 2) generation of reactive oxygen species responsible for peptide oxidation upon photoactivation under mild conditions; and 3) relatively easy incorporation of a ligand on the IrIII center for specific interactions with amyloidogenic peptides. Biochemical and biophysical investigations illuminate that the oxidation of representative amyloidogenic peptides (i.e., amyloid-β, α-synuclein, and human islet amyloid polypeptide) is promoted by light-activated Ir-1, which alters the conformations and aggregation pathways of the peptides. Additionally, their potential oxidation sites are identified as methionine, histidine, or tyrosine residues. Overall, our studies on Ir-1 demonstrate the feasibility of devising metal complexes as chemical tools suitable for elucidating the nature of amyloidogenic peptides at the molecular level, as well as controlling their aggregation.

Calprotectin influences the aggregation of metal-free and metal-bound amyloid-β by direct interaction

“…All experiments with Aβ were performed according to previously published methods. 74,75,[82][83][84] Aβ peptides were dissolved in ammonium hydroxide (NH 4 OH, 1% v/v, aq), aliquoted, lyophilized, and stored at −80 °C. A stock soluƟon (ca.…”

“…200 µM) was prepared by dissolving Aβ in NH 4 OH (1% w/v, aq, 10 µL) followed by dilution with ddH 2 O, as reported previously. 74,75,[82][83][84] The Aβ 40 concentration was determined by measuring the absorbance of the solution at 280 nm (ε = 1450 M -1 cm -1 for Aβ 40 ; ε = 1490 M -1 cm -1 for Aβ 42 ). HEPES [4-(2hydroxyethyl)-1-piperazineethanesulfonic acid; 20 mM], pH 7.4 (for metal-free and Zn(II) samples) and pH 6.6 (for Cu(II) samples), 150 mM NaCl was used for the studies.…”

“…The Aβ peptide experiments described above were analyzed by gel electrophoresis with two different visualization methods: (i) Western blotting (gel/Western blot) with two different antibodies [anti-Aβ antibody (6E10; Covance, Princeton, NJ, USA) or anti-S100A9 antibody (Santa Cruz Biotechnology, Dallas, TX, USA)]; 74,75,[82][83][84] (ii) Coomassie blue staining. Each sample from the experiments was separated using a 10−20% gradient Tris-tricine gel (Thermo Fisher, Grand Island, NY, USA).…”

“…Protein samples for TEM measurements were prepared following previously reported methods. 74,75,[82][83][84] Glow discharged grids (Formvar/Carbon 300-mesh, Electron Microscopy Sciences, Hatfield, PA, USA) were treated with samples from the experiments (5 µL) for 2 min at room temperature. Excess sample was removed with filter paper and the grids were washed with ddH 2 O three times.…”

DFT Investigation of Ligand Photodissociation in [RuII(tpy)(bpy)(py)]2+ and [RuII(tpy)(Me2bpy)(py)]2+ Complexes

“…Metal centers of interest include Pt(IV), 19 Re(I), 20 and Ir(III) 21 as well as complexes containing Ru(II), which have all been investigated extensively. Photoactivatable Ru(II)-centered chaperones are typically composed of tridentate or bidentate chelators, such as 2,2′:6′,2″-terpyridine (tpy), 2,2′-bipyridine (bpy), and 1,10-phenanthroline (phen) and their derivatives as ancillary ligands and one or more monodentate ligands as the active species for release.…”