Parkinson's disease (PD) is a neurologic disorder characterized by dopaminergic cell death in the substantia nigra. PD pathogenesis involves mitochondrial dysfunction, proteasome impairment, and α-synuclein aggregation, insults that may be especially toxic to oxidatively stressed cells including dopaminergic neurons. The enzyme methionine sulfoxide reductase A (MsrA) plays a critical role in the antioxidant response by repairing methionine-oxidized proteins and by participating in cycles of methionine oxidation and reduction that have the net effect of consuming reactive oxygen species. Here, we show that MsrA suppresses dopaminergic cell death and protein aggregation induced by the complex I inhibitor rotenone or mutant α-synuclein, but not by the proteasome inhibitor MG132. By comparing the effects of MsrA and the small-molecule antioxidants N-acetyl-cysteine and vitamin E, we provide evidence that MsrA protects against PD-related stresses primarily via methionine sulfoxide repair rather than by scavenging reactive oxygen species. We also demonstrate that MsrA efficiently reduces oxidized methionine residues in recombinant α-synuclein. These findings suggest that enhancing MsrA function may be a reasonable therapeutic strategy in PD. Keywords aggresome; dopamine; glutathione; heat shock protein; methionine sulfoxide reductase; neurodegeneration; oxidative stress; Parkinson's disease; proteasome; protofibril; rotenone; synuclein Parkinson's disease (PD) is a neurologic disorder that involves a selective loss of dopaminergic neurons from the substantia nigra [1,2]. The postmortem brains of PD patients are characterized by reduced activity of mitochondrial complex I, an enzyme of the mitochondrial electron transport chain [3,4]. In turn, this defect may cause a 'leakage' of electrons from mitochondria, leading to the accumulation of reactive oxygen species (ROS) that damage *Corresponding author. Address: Jean-Christophe Rochet, Department of Medicinal Chemistry and Molecular Pharmacology, Purdue University, 575 Stadium Mall Drive, RHPH 410A, West Lafayette, Indiana, 47907-209147907- . Fax: 765-494-1414. E-mail: rochet@pharmacy.purdue.edu. Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. NIH Public Access Author ManuscriptFree Radic Biol Med. Author manuscript; available in PMC 2009 August 1. NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript proteins, lipids, and nucleic acids [3,5]. The brains of PD patients also show evidence of impaired proteasomal function [6], a defect that results in increased oxidative stress and decreased elimination...

Alpha-synuclein (α-Syn) is a 140 aa presynaptic protein which belongs to a group of natively unfolded proteins that are unstructured in aqueous solutions. The aggregation rate of α-Syn is accelerated in the presence of physiological levels of cellular polyamines. Here we applied single molecule AFM force spectroscopy to characterize the effect of spermidine on the very first stages of α-Syn aggregation – misfolding and assembly into dimers. Two α-Syn variants, the wild-type (WT) protein and A30P, were studied. The two protein molecules were covalently immobilized at the C-terminus, one at the AFM tip and the other on the substrate, and intermolecular interactions between the two molecules were measured by multiple approach-retraction cycles. At conditions close to physiological ones at which α-Syn misfolding is a rare event, the addition of spermidine leads to a dramatic increase in the propensity of the WT and mutant proteins to misfold. Importantly, misfolding is characterized by a set of conformations, and A30P changes the misfolding pattern as well as the strength of the intermolecular interactions. Together with the fact that spermidine facilitates late stages of α-Syn aggregation, our data demonstrate that spermidine promotes the very early stages of protein aggregation including α-Syn misfolding and dimerization. This finding suggests that increased levels of spermidine and potentially other polyamines can initiate the disease-related process of α-Syn.

Misfolding and subsequent aggregation of alpha-synuclein (α-Syn) protein are critically involved in the development of several neurodegenerative diseases, including Parkinson’s disease (PD). Three familial single point mutations, A30P, E46K, and A53T, correlate with early-onset PD; however the molecular mechanism of the effects of these mutations on the structural properties of α-Syn and its propensity to misfold remains unclear. Here, we address this issue utilizing a single molecule AFM force spectroscopy approach in which structural details of dimers formed by all four variants of α-Syn are characterized. Analysis of the force spectroscopy data reflecting contour length distribution for α-Syn dimer dissociation suggests that multiple segments are involved in the assembly of the dimer. The interactions are not limited to the central non-amyloid-beta component (NAC) of the protein, but rather expand beyond this segment. All three mutations alter the protein’s folding and interaction patterns affecting interactions far beyond their immediate locations. Implementation of these findings to our understanding of α-Syn aggregation pathways is discussed.

Mutations in the gene encoding DJ-1 have been identified in patients with familial Parkinson's disease (PD) and are thought to inactivate a neuroprotective function. Oxidation of the sulfhydryl group to a sulfinic acid on cysteine residue C106 of DJ-1 yields the "2O " form, a variant of the protein with enhanced neuroprotective function. We hypothesized that some familial mutations disrupt DJ-1 activity by interfering with conversion of the protein to the 2O form. To address this hypothesis, we developed a novel quantitative mass spectrometry approach to measure relative changes in oxidation at specific sites in mutant DJ-1 as compared with the wild-type protein. Treatment of recombinant wild-type DJ-1 with a 10-fold molar excess of H 2 O 2 resulted in a robust oxidation of C106 to the sulfinic acid, whereas this modification was not detected in a sample of the familial PD mutant M26I exposed to identical conditions. Methionine oxidized isoforms of wild-type DJ-1 were depleted, presumably as a result of misfolding and aggregation, under conditions that normally promote conversion of the protein to the 2O form. These data suggest that the M26I familial substitution and methionine oxidation characteristic of sporadic PD may disrupt DJ-1 function by disfavoring a site-specific modification required for optimal neuroprotective activity. Our findings indicate that a single amino acid substitution can markedly alter a protein's ability to undergo oxidative modification, and they imply that stimulating the

Background α-Synuclein (aSyn) aggregation is thought to play a central role in neurodegenerative disorders termed synucleinopathies, including Parkinson’s disease (PD). Mouse aSyn contains a threonine residue at position 53 that mimics the human familial PD substitution A53T, yet in contrast to A53T patients, mice show no evidence of aSyn neuropathology even after aging. Here, we studied the neurotoxicity of human A53T, mouse aSyn, and various human-mouse chimeras in cellular and in vivo models, as well as their biochemical properties relevant to aSyn pathobiology. Methods Primary midbrain cultures transduced with aSyn-encoding adenoviruses were analyzed immunocytochemically to determine relative dopaminergic neuron viability. Brain sections prepared from rats injected intranigrally with aSyn-encoding adeno-associated viruses were analyzed immunohistochemically to determine nigral dopaminergic neuron viability and striatal dopaminergic terminal density. Recombinant aSyn variants were characterized in terms of fibrillization rates by measuring thioflavin T fluorescence, fibril morphologies via electron microscopy and atomic force microscopy, and protein-lipid interactions by monitoring membrane-induced aSyn aggregation and aSyn-mediated vesicle disruption. Statistical tests consisted of ANOVA followed by Tukey’s multiple comparisons post hoc test and the Kruskal-Wallis test followed by a Dunn’s multiple comparisons test or a two-tailed Mann-Whitney test. Results Mouse aSyn was less neurotoxic than human aSyn A53T in cell culture and in rat midbrain, and data obtained for the chimeric variants indicated that the human-to-mouse substitutions D121G and N122S were at least partially responsible for this decrease in neurotoxicity. Human aSyn A53T and a chimeric variant with the human residues D and N at positions 121 and 122 (respectively) showed a greater propensity to undergo membrane-induced aggregation and to elicit vesicle disruption. Differences in neurotoxicity among the human, mouse, and chimeric aSyn variants correlated weakly with differences in fibrillization rate or fibril morphology. Conclusions Mouse aSyn is less neurotoxic than the human A53T variant as a result of inhibitory effects of two C-terminal amino acid substitutions on membrane-induced aSyn aggregation and aSyn-mediated vesicle permeabilization. Our findings highlight the importance of membrane-induced self-assembly in aSyn neurotoxicity and suggest that inhibiting this process by targeting the C-terminal domain could slow neurodegeneration in PD and other synucleinopathy disorders.

α-Synuclein (aSyn) aggregation is thought to play a central role in neurodegenerative disorders termed synucleinopathies, including Parkinson's disease (PD). Mouse aSyn contains a threonine residue at position 53 that mimics the human familial PD substitution A53T, yet in contrast to A53T patients, mice show no evidence of aSyn neuropathology even after aging.Here we studied the neurotoxicity of human A53T, mouse aSyn, and various human-mouse chimeras in cellular and in vivo models as well as their biochemical properties relevant to aSyn pathobiology. We report that mouse aSyn is less neurotoxic than the human A53T variant as a result of inhibitory effects of two C-terminal amino acid substitutions on membrane-induced aSyn aggregation and aSyn-mediated vesicle permeabilization. Our findings highlight the importance of membrane-induced self-assembly in aSyn neurotoxicity and suggest that inhibiting this process by targeting the C-terminal domain could slow neurodegeneration in PD and other synucleinopathy disorders.The goal of this study was to investigate the impact of the mismatches between m-aSyn 51 and h-aSyn A53T on aSyn neurotoxicity. Previously it was reported that rat aSyn (which differs 52 from the mouse protein by a single G-to-S mismatch at position 121) failed to trigger neuronal 53 cell death when expressed from a lentiviral vector infused in rat SN, in contrast to h-aSyn WT 54 and h-aSyn A53T (27). Similarly, we found that rat aSyn had a reduced ability to trigger nigral 55 dopaminergic cell death compared to h-aSyn A53T in the rAAV-mediated overexpression model 56 in the rat (28). Based on the close sequence similarity between mouse and rat aSyn, we 57 hypothesized that the mouse protein is less neurotoxic than h-aSyn A53T, potentially because 58 the toxic consequences of having a threonine residue at position 53 are alleviated by mismatch 59 residues elsewhere in the murine sequence. To address this hypothesis, we compared h-aSyn 60 A53T, m-aSyn, and various human-mouse chimeras in terms of their ability to elicit 61 neurodegeneration in cellular and animal models relevant to PD and other synucleinopathy 62 disorders. The human and mouse proteins and a subset of chimeras were further examined for 63 their ability to form amyloid-like fibrils in the absence of membranes, undergo membrane-64 induced aSyn aggregation, and trigger membrane permeabilization. 65 66 Results 67 Neurotoxicity of aSyn variants in primary midbrain culture 68In the first part of our study, we used a primary mesencephalic cell culture model to 69 examine the effects of amino acid variations between m-aSyn and h-aSyn A53T on aSyn 70 neurotoxicity. In addition to h-aSyn A53T and m-aSyn, two chimeric variants were analyzed: (i) 71 h-aSyn Chimera, consisting of h-aSyn with the human-to-mouse substitutions A53T, D121G, 72 and N122S; and (ii) m-aSyn Chimera, consisting of m-aSyn with the mouse-to-human 73 substitutions G121D and S122N ( Figure 1B). We chose to examine the effects of substitutions 74 at positions 121 and 122 based on ...