Weihong Du

Palladium complexes affect the aggregation of human prion protein PrP106-126.

Many neurodegenerative disorders are induced by protein conformational change. Prion diseases are characterized by protein conformational conversion from a normal cellular form (PrP(C)) to an abnormal scrapie isoform (PrP(Sc)). PrP106-126 is an accepted model for studying the characteristics of PrP(Sc) because they share many biological and physiochemical properties. To understand how metal complexes affect the property of the prion peptide, the present work investigated interactions between Pd complexes and PrP106-126 based on our previous research using Pt and Au complexes to target the peptide. The selected compounds (Pd(phen)Cl(2), Pd(bipy)Cl(2), and Pd(en)Cl(2)) showed strong binding affinity to PrP106-126 and affected the conformation and aggregation of this active peptide in a different binding mode. Our results indicate that it may be the metal ligand-induced spatial effect rather the binding affinity that contributes to better inhibition on peptide aggregation. This finding would prove valuable in helping design and develop novel metallodrugs against prion diseases.

Gold complexes inhibit the aggregation of prion neuropeptides

Prion diseases are characterized by conformational conversion of prion protein from a normal cellular form to an abnormal scrapie isoform (PrPSc). PrP106–126 is a prion neuropeptide and an accepted model used to study the characteristics of PrPSc because such a model has biological and physiochemical properties similar to those of PrPSc. Some metal complexes have a strong binding affinity for PrP106–126 and a good inhibitory effect against amyloid fibril formation. However, the effects of the metal ligand configuration on peptide binding and aggregation are not well known. To investigate interaction and peptide aggregation between prion neuropeptides and two gold complexes with different ligand configurations ([Au(bpy)Cl2]PF6 and [Au(dien)Cl]Cl2, where bpy is 2,2′-bipyridine and dien is diethylenetriamine), six prion peptides with either a His111-mutated or a Met109/112-mutated residue were used in this study. The selection of the mutant was based on the corresponding neuropeptide from other species. The results showed that the aromatic gold complex [Au(bpy)Cl2]PF6 exhibits better binding affinity and a better inhibitory effect against peptide aggregation than the tridentate complex [Au(dien)Cl]Cl2. For the sequence–specific PrP106–126 and its mutants, His111 plays the most important role in peptide aggregation and binding affinity. Furthermore, Met112 has a greater effect on the binding affinity than Met109. Compared with the mutated short 14 amino acid peptides, the hydrophobic region of PrP106–126 contributes to both binding affinity and self-aggregation behavior. This work will help to understand and develop potential metallodrugs against amyloid disorder.Graphical Abstract

Structural and Functional Characterization of a Novel α-Conotoxin Mr1.7 from Conus marmoreus Targeting Neuronal nAChR α3β2, α9α10 and α6/α3β2β3 Subtypes

In the present study, we synthesized and, structurally and functionally characterized a novel α4/7-conotoxin Mr1.7 (PECCTHPACHVSHPELC-NH2), which was previously identified by cDNA libraries from Conus marmoreus in our lab. The NMR solution structure showed that Mr1.7 contained a 310-helix from residues Pro7 to His10 and a type I β-turn from residues Pro14 to Cys17. Electrophysiological results showed that Mr1.7 selectively inhibited the α3β2, α9α10 and α6/α3β2β3 neuronal nicotinic acetylcholine receptors (nAChRs) with an IC50 of 53.1 nM, 185.7 nM and 284.2 nM, respectively, but showed no inhibitory activity on other nAChR subtypes. Further structure-activity studies of Mr1.7 demonstrated that the PE residues at the N-terminal sequence of Mr1.7 were important for modulating its selectivity, and the replacement of Glu2 by Ala resulted in a significant increase in potency and selectivity to the α3β2 nAChR. Furthermore, the substitution of Ser12 with Asn in the loop2 significantly increased the binding of Mr1.7 to α3β2, α3β4, α2β4 and α7 nAChR subtypes. Taken together, this work expanded our knowledge of selectivity and provided a new way to improve the potency and selectivity of inhibitors for nAChR subtypes.

Inhibition of human prion neuropeptide PrP106-126 aggregation by hexacoordinated ruthenium complexes

Prion disease is a neurodegenerative disorder that can occur among humans and other animals. The aberrant isoform of prion protein PrP(Sc) has been identified as the infectious agent. The neuropeptide PrP106-126 has been widely used as a suitable model to study the biological and physiochemical properties of PrP(Sc). PrP106-126 shares several physicochemical and biological properties with PrP(Sc), including cellular toxicity, fibrillogenesis, and membrane-binding affinity. Ruthenium complexes are commonly employed in anti-cancer studies due to their low cellular toxicity. In this study, six hexacoordinated ruthenium complexes with different molecular configurations were used to investigate their effects on PrP106-126 aggregation inhibition. Results revealed that the interaction between the complexes and the peptide included metal coordination and hydrophobic interaction mainly. Those complexes with aromatic structure displayed better inhibitory effects, although they only had a common binding affinity to PrP106-126. This study provided better understanding on the interaction of metal complexes with PrP106-126 and paved the way for potential Ru-based metallodrugs against prion diseases.

Regulation of Aggregation Behavior and Neurotoxicity of Prion Neuropeptides by Platinum Complexes

Prion diseases belong to a group of infectious, fatal neurodegenerative disorders. The conformational conversion of a cellular prion protein (PrP(C)) into an abnormal misfolded isoform (PrP(Sc)) is the key event in prion disease pathology. PrP106-126 resembles PrP(Sc) in some physicochemical and biological characteristics, such as apoptosis induction in neurons, fibrillar formation, and mediation of the conversion of native cellular PrP(C) to PrP(Sc). Numerous studies have been conducted to explore the inhibiting methods on the aggregation and neurotoxicity of prion neuropeptide PrP106-126. We showed that PrP106-126 aggregation, as assessed by fluorescence assay and atomic force microscopy, is inhibited by platinum complexes cisplatin, carboplatin, and Pt(bpy)Cl2. ESI-MS and NMR assessments of PrP106-126 and its mutant peptides demonstrate that platinum complexes bind to the peptides in coordination and nonbonded interactions, which rely on the ligand properties and the peptide sequence. In peptides, methionine residue is preferred as a potent binding site over histidine residue for the studied platinum complexes, implying a typical thiophile characteristic of platinum. The neurotoxicity induced by PrP106-126 is better inhibited by Pt(bpy)Cl2 and cisplatin. Furthermore, the ligand configuration contributes to both the binding affinity and the inhibition of peptide aggregation. The pursuit of novel platinum candidates that selectively target prion neuropeptide is noteworthy for medicinal inorganic chemistry and chemical biology.

Effects of gold complexes on the assembly behavior of human islet amyloid polypeptide.

Human islet amyloid polypeptide (hIAPP) is a well-known amyloid protein that is associated with type II diabetes. Inhibitors of this peptide include aromatic organic molecules, short peptides, and metal complexes, such as zinc, ruthenium and vanadium compounds. Various metal ions and their complexes affect the fibrillization of hIAPP in different action modes. However, the assembly mechanism of the peptide remains unclear. This study evaluated the inhibitory effects of three gold complexes with different nitrogen-containing aromatic ligands, namely, [Au(bipy)Cl2][PF6] (1), [Au(Ph2bpy)Cl2]Cl (2), and [Au(phen)Cl2]Cl (3), on the amyloid fibrillization of hIAPP. The complexes interacted with the peptide mainly through hydrophobic interaction and metal coordination. The concentration dependence of hIAPP aggregation on gold complex indicated that the assembly behavior of hIAPP is significantly affected by these compounds. The gold complexes inhibited peptide aggregation through dimerization and stabilized the peptide to monomers. Gold ion was found to be a key influencing factor of the binding mode and assembly behavior of hIAPP. The different effects of the complexes on peptide aggregation might be attributed to their special ligands. This study provided insights into the inhibitory mechanism of gold complexes against hIAPP fibrillization.

Solution 1H NMR study of the active site structure for the double mutant H64Q/V68F cyanide complex from mouse neuroglobin.

Solution (1)H NMR spectroscopy has been carried out to investigate the molecular and electronic structures of the active site in H64Q/V68F double mutant mouse neuroglobin in the cyanomet form. Two heme orientations resulting from a 180 degrees rotation about the alpha-gamma-meso axis were observed with a population ratio about 1:1, and the clearly distinguished B isomer was used to perform the study. Based on the analysis of the dipolar shifts and paramagnetic relaxation constants, the distal Gln(64)(E7) side chain is obtained to adopt an orientation that may produce hydrogen bond between the N(epsilon)H(1) and the Fe-bound cyanide. The side chain of Phe(68)(E11) is oriented out of the heme pocket just like that in triple mutant of cyanide complex of sperm whale myoglobin. A 15 degrees rotation of the imidazole ring in axial His(96) is observed, which is close to the varphi angle determined from the crystal structure of NgbCO. The quantitative determinations of the orientation and anisotropies of the paramagnetic susceptibility tensor reveal that cyanide is tilted by 8 degrees from the heme normal which allows for contact to the Gln(64)(E7) N(epsilon)H(1). The E7 and E11 residues appear to control the direction and the extent of tilt of the bound ligand. Furthermore, the tilt of the ligand has no obvious influence on the heme heterogeneity of cyanide ligation for isomer A/B of the wild type and mutant protein, indicating that factors other than steric effects, such as polarity of heme pocket, impacts on ligand binding affinity.

Disaggregation of human islet amyloid polypeptide fibril formation by ruthenium polypyridyl complexes

The toxicity of amyloid proteins is associated with many degenerative and systematic diseases. The aggregation of human islet amyloid polypeptide may induce pancreatic β-cell death, which is linked to type II diabetes. Ruthenium complexes are inhibitors of various proteins and potential anticancer metallodrugs, which can also be used to disaggregate amyloid proteins. This work reported that several ruthenium polypyridyl complexes remarkably affected the peptide aggregation by predominant hydrophobic interaction and metal coordination, as reflected by thermodynamic parameters and mass spectrometry analysis. Morphology and particle size analysis showed that the amyloid fibrils were disaggregated from long fibrils into small nano particles. Addition of these complexes also decreased the cytotoxicity induced by the peptide. The results indicated that ruthenium polypyridyl complexes may be potential metallodrugs to treat amyloidosis.

Molecular dynamics simulation of carboxy and deoxy human cytoglobin in solution

Cytoglobin (Cgb), the fourth member of the vertebrate heme globin family, is widely expressed in mammalian tissues, and reversibly binds to CO, O(2) and other small ligands. The diverse functions of Cgb may include ligand transport, redox reactions and enzymatic catalysis. Recent studies indicate that Cgb is a potential gene medicine for fibrosis and cancer therapy. In the present work, molecular dynamics (MD) simulations were performed to investigate the functionally related structural properties and dynamic characteristics in carboxy and deoxy human Cgb. The simulation results showed that the loop regions and internal cavities were significantly affected through the binding of an exogenous ligand. The AB, GH and EF loops were found to undergo significant rearrangement and this led to distinct cavity adjustments in Xe2, Xe4 and the distal pocket. In addition, solvent accessibility and torsion angle analyses revealed an interactive distal network comprised of His(81)(E7), Leu(46)(B10) and Arg(84)(E10). The MD study of carboxy and deoxy human Cgb revealed that CO-ligated Cgb modulates the protein conformation primarily by loop and cavity rearrangements rather than the heme sliding mechanism found in neuroglobin (Ngb). The significant differences between Cgb and Ngb in the loop and cavity properties are presumably linked to their various biological functions.

Roles of DMSO-type ruthenium complexes in disaggregation of prion neuropeptide PrP106–126

Ruthenium complexes are potential anticancer metallodrugs and inhibitors of various proteins, such as enzymes and even amyloid peptides. Studies on Aβ protein, human islet amyloid polypeptide, and prion neuropeptide have indicated that Ru complexes can inhibit amyloidosis. However, the interaction mechanism of peptides with Ru complexes remains unclear. In this study, we selected four dimethyl sulfoxide (DMSO)-type Ru complexes containing large aromatic ligands to explore and compare the interactions of Ru complexes with the prion neuropeptide PrP106–126. Results showed that, unlike new anti-tumor metastasis inhibitor-A-like compounds, these complexes can bind to PrP106–126 mainly through metal coordination and hydrophobic interaction. The Ru complexes disaggregated the PrP106–126 fibrils into scattered fragments or amorphous forms, thereby reducing the toxicity of PrP106–126. Among the four Ru complexes, complex 1, which consists of bipyridyl and DMSO ligands, exhibited the highest disaggregation ability and relatively high cell viability, which may be attributed to its molecular configuration and low cytotoxicity. These results suggested that Ru complexes are promising metallodrugs against amyloidosis-related diseases.