[Show abstract][Hide abstract] ABSTRACT: Platinum phenanthroline complexes have been found to inhibit Aβ aggregation and reduce Aβ caused neurotoxicity. Our previous results revealed the synergistic roles of phenanthroline ligand and Pt(ii) coordination in the inhibition of Aβ aggregation. In this work, the reactions of PtCl2(phen) with metal bound Aβ complexes were investigated. HPLC results show that the copper coordination decreases the reaction rate of PtCl2(phen) with Aβ1-16 and influences the distribution of products on HPLC profiles. EPR results reveal that Cu(2+) remains coordinated to the Aβ peptide upon the binding of [Pt(phen)](2+), however, the Cu(2+) coordination sites are changed. The formation of bimetallic coordination complex [Pt(phen)+Aβ1-16+Cu(II)] was confirmed by ESI-MS. Tandem MS analysis shows that, similar to the reaction of apo-Aβ peptide, the His6/His14 chelation is also the preferred binding mode for [Pt(phen)](2+) in the presence of copper ions. EPR spectra suggest that the binding of [Pt(phen)](2+) alters the copper coordination from mode I to mode II in Aβ. Tandem MS analysis indicates that His13 and N-terminal amine could be involved in the Cu(2+) coordination in the bimetallic adduct. Similar results were observed in the reaction of Zn(2+) bound Aβ peptide, although the different zinc binding residues were detected in the bimetallic complex. These results indicate that the binding of platinum complex disturbs the most favorable coordination sphere of Cu(2+)/Zn(2+) and turns these metal ions to the secondary coordination site on Aβ. The release of Cu(2+)/Zn(2+) occurs at low pH. This result suggests that the binding of [Pt(phen)](2+) scaffold could interfere with the binding of Zn(2+) and Cu(2+) to Aβ, thus reducing the metal-induced Aβ aggregation and toxicity.
[Show abstract][Hide abstract] ABSTRACT: Human copper transporter 1 (hCTR1) facilitates the cellular uptake of cisplatin, and the extracellular N-terminal domain has been proven to coordinate to platinum drugs. It has been reported that the intracellular C-terminal motif is crucial for the function of hCTR1 in cisplatin influx. In this work, we conduct reactions of the intracellular motif with platinum drugs. The octapeptide from the C-terminal domain of hCTR1 is used, and the reactions are investigated using ultraviolet, high-performance liquid chromatography, electrospray ionization mass spectrometry, and nuclear magnetic resonance spectroscopy. Results show that the C8 peptide is highly reactive to cisplatin and oxaliplatin, and the -HCH sequence is the most favorable binding site of platinum agents. Cisplatin first binds to the cysteine residues in the reaction with the C8 peptide. The ammine ligand, even trans to a thiol ligand, can remain coordinated in platination adducts for a >12 h reaction. Intramolecular platinum migration was observed in the C8 peptide, and the ammine ligands remain coordinated to platinum during this process. This result indicates that hCTR1 can transfer cisplatin in the active form through a trans chelation process. These findings provide insight into the mechanism of the C-terminus of hCTR1 in the transfer of platinum drugs from the trimeric pore of hCTR1 to the cytoplasm.
[Show abstract][Hide abstract] ABSTRACT: A novel ratiometric fluorescent peptidyl chemosensor (Dansyl-Cys-Pro-Gly-Cys-Trp-NH(2), D-P5) for metal ions detection has been synthesized via Fmoc solid-phase peptide synthesis. The chemosensor exhibited a high selectivity for Cd(2+) over other metal ions including competitive transition and Group I and II metal ions in neutral pH. The fluorescence emission intensity of D-P5 was significantly enhanced in the presence of Cd(2+) by fluorescent resonance energy transfer (FRET) and chelation enhanced fluorescence (CHEF) effects. The binding stoichiometry, detection limit, binding affinity, reversibility and pH sensitivity of the sensor for Cd(2+) were investigated.