Mechanism of copper(II)-induced misfolding of Parkinson's disease protein

Antioxidant gene therapy against neuronal cell death

Oxidative stress is a common hallmark of neuronal cell death associated with neurodegenerative disorders such as Alzheimer's disease, Parkinson's disease, as well as brain stroke/ischemia and traumatic brain injury. Increased accumulation of reactive species of both oxygen (ROS) and nitrogen (RNS) has been implicated in mitochondrial dysfunction, energy impairment, alterations in metal homeostasis and accumulation of aggregated proteins observed in neurodegenerative disorders, which lead to the activation/modulation of cell death mechanisms that include apoptotic, necrotic and autophagic pathways. Thus, the design of novel antioxidant strategies to selectively target oxidative stress and redox imbalance might represent important therapeutic approaches against neurological disorders. This work reviews the evidence demonstrating the ability of genetically encoded antioxidant systems to selectively counteract neuronal cell loss in neurodegenerative diseases and ischemic brain damage. Because gene therapy approaches to treat inherited and acquired disorders offer many unique advantages over conventional therapeutic approaches, we discussed basic research/clinical evidence and the potential of virus-mediated gene delivery techniques for antioxidant gene therapy.

Secondary structure preferences of mn (2+) binding sites in bacterial proteins

3D structures of proteins with coordinated Mn²⁺ ions from bacteria with low, average, and high genomic GC-content have been analyzed (149 PDB files were used). Major Mn²⁺ binders are aspartic acid (6.82% of Asp residues), histidine (14.76% of His residues), and glutamic acid (3.51% of Glu residues). We found out that the motif of secondary structure “beta strand-major binder-random coil” is overrepresented around all the three major Mn²⁺ binders. That motif may be followed by either alpha helix or beta strand. Beta strands near Mn²⁺ binding residues should be stable because they are enriched by such beta formers as valine and isoleucine, as well as by specific combinations of hydrophobic and hydrophilic amino acid residues characteristic to beta sheet. In the group of proteins from GC-rich bacteria glutamic acid residues situated in alpha helices frequently coordinate Mn²⁺ ions, probably, because of the decrease of Lys usage under the influence of mutational GC-pressure. On the other hand, the percentage of Mn²⁺ sites with at least one amino acid in the “beta strand-major binder-random coil” motif of secondary structure (77.88%) does not depend on genomic GC-content.

Brain cholesterol homeostasis in Wilson disease

Wilson disease (WD) is an autosomal recessive inherited disorder of copper (Cu) metabolism, resulting in pathological accumulation of Cu in many organs and tissues, predominantly in the liver and brain. There clearly is a close and complex relationship between Cu and the cholesterol's metabolic pathway; therefore any theory about the cholesterol metabolism in the brain of patients with WD must take it into account. The hypothesis presented in this paper is that the imbalance in cerebral copper homeostasis caused by WD may plays a key role in the derangement of the cholesterol homeostasis in the brain, and thus promoting the observed WD related neurological disorders.

Insight into α-synuclein plasticity and misfolding from differential micelle binding

Misfolded species of the 140-residue protein α-synuclein (αS) are implicated in the demise of dopaminergic neurons, resulting in fatal neurodegeneration. The intrinsically unstructured protein binds curved synaptic vesicle membranes in helical conformations but misfolds into amyloid fibrils via β-sheet interactions. Breaks in helical αS conformation may offer a pathway to transition from helical to sheet conformation. Here, we explore the evolution of broken αS helix conformations formed in complex with SDS and SLAS micelles by molecular dynamics simulations. The population distribution of experimentally observed αS conformations is related to the spatial concentration of intrinsic micelle shape perturbations. For the success of micelle-induced αS folding, we posit the length of the first helical segment formed, which controls micelle ellipticity, to be a key determinant. The degree of micelle curvature relates to the arrangement and segmental motions of helical secondary structure elements. A criterion for assessing the reproduction of such intermediate time scale protein dynamics is introduced by comparing the sampling of experimental and simulated spin label distributions. Finally, at the sites of breaks in the elongated, marginally stable αS helix, vulnerability to forming a transient, intramolecular β-sheet is identified. Upon subsequent intermolecular β-sheet pairing, pathological αS amyloid formation from initial helical conformation is thus achievable.

Low levels of copper disrupt brain amyloid-β homeostasis by altering its production and clearance

Whereas amyloid-β (Aβ) accumulates in the brain of normal animals dosed with low levels of copper (Cu), the mechanism is not completely known. Cu could contribute to Aβ accumulation by altering its clearance and/or its production. Because Cu homeostasis is altered in transgenic mice overexpressing Aβ precursor protein (APP), the objective of this study was to elucidate the mechanism of Cu-induced Aβ accumulation in brains of normal mice and then to explore Cu's effects in a mouse model of Alzheimer's disease. In aging mice, accumulation of Cu in brain capillaries was associated with its reduction in low-density lipoprotein receptor-related protein 1 (LRP1), an Aβ transporter, and higher brain Aβ levels. These effects were reproduced by chronic dosing with low levels of Cu via drinking water without changes in Aβ synthesis or degradation. In human brain endothelial cells, Cu, at its normal labile levels, caused LRP1-specific down-regulation by inducing its nitrotyrosination and subsequent proteosomal-dependent degradation due in part to Cu/cellular prion protein/LRP1 interaction. In APP(sw/0) mice, Cu not only down-regulated LRP1 in brain capillaries but also increased Aβ production and neuroinflammation because Cu accumulated in brain capillaries and, unlike in control mice, in the parenchyma. Thus, we have demonstrated that Cu's effect on brain Aβ homeostasis depends on whether it is accumulated in the capillaries or in the parenchyma. These findings should provide unique insights into preventative and/or therapeutic approaches to control neurotoxic Aβ levels in the aging brain.

Spectroscopic evidence for polymorphic aggregates formed by amyloid-β fragments

Understanding the structure of amyloid-β (Aβ) aggregates is a key step towards elucidating the pathology of Alzheimer's disease. In this work, three fragments of the Aβ(1-42) protein, Aβ(1-25) (DAEFRHDSGYEVHHQKLVFFAEDVG), Aβ(25-35) (GSNKGAIIGLM), and Aβ(33-42) (GLMVGGVVIA), were synthesized, and their aggregated structures were examined by linear infrared spectroscopy in the amide-I (mainly the C=O stretching) region. The structures of the formed aggregates were found to be both sequence and pH dependent. The results suggest that instead of forming matured fibrils, as in the case of full-length Aβ(1-42), both Aβ(1-25) and Aβ(33-42) form a mixture of threadlike β-sheet fibril, soluble β-sheet oligomer, and random coil structures. The β-sheet conformations were found to be mainly antiparallel for the former and both parallel and antiparallel for the latter. However, the Aβ(25-35) fragment was found to form assembled fibrils containing predominantly parallel β-sheets. The conformation and morphology of the aggregates were also confirmed by circular dichroism measurements and transmission electron microscopy. Factors influencing the structures of the aggregates formed by the Aβ fragments were discussed.

The unravelling of metabolic dysfunctions linked to metal-associated diseases by blue native polyacrylamide gel electrophoresis

Gel electrophoresis is routinely used to separate and analyse macromolecules in biological systems. Although many of these electrophoretic techniques necessitate the denaturing of the analytes prior to their analysis, blue native polyacrylamide gel electrophoresis (BN-PAGE) permits the investigation of proteins/enzymes and their supramolecular structures such as the metabolon in native form. This attribute renders this analytical tool conducive to deciphering the metabolic perturbations invoked by metal toxicity. In this review, we elaborate on how BN-PAGE has led to the discovery of the dysfunctional metabolic pathways associated with disorders such as Alzheimer's disease, Parkinson's disease, and obesity that have been observed as a consequence of exposure to various metal toxicants.