Browsing by Author "Wu, Chun-Xiang"

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    Caspase-1 causes truncation and aggregation of the Parkinson's disease-associated protein α-synuclein
    (National Academy of Sciences, 2016-08-23) Wang, Wei; Nguyen, Linh T. T.; Burlak, Christopher; Chegini, Fariba; Guo, Feng; Chataway, Tim; Ju, Shulin; Fisher, Oriana S.; Miller, David W.; Datta, Debajyoti; Wu, Fang; Wu, Chun-Xiang; Landeru, Anuradha; Wells, James A.; Cookson, Mark R.; Boxer, Matthew B.; Thomas, Craig J.; Gai, Wei Ping; Ringe, Dagmar; Petsko, Gregory A.; Hoang, Quyen Q.; Department of Biochemistry & Molecular Biology, IU School of Medicine
    The aggregation of α-synuclein (aSyn) leading to the formation of Lewy bodies is the defining pathological hallmark of Parkinson's disease (PD). Rare familial PD-associated mutations in aSyn render it aggregation-prone; however, PD patients carrying wild type (WT) aSyn also have aggregated aSyn in Lewy bodies. The mechanisms by which WT aSyn aggregates are unclear. Here, we report that inflammation can play a role in causing the aggregation of WT aSyn. We show that activation of the inflammasome with known stimuli results in the aggregation of aSyn in a neuronal cell model of PD. The insoluble aggregates are enriched with truncated aSyn as found in Lewy bodies of the PD brain. Inhibition of the inflammasome enzyme caspase-1 by chemical inhibition or genetic knockdown with shRNA abated aSyn truncation. In vitro characterization confirmed that caspase-1 directly cleaves aSyn, generating a highly aggregation-prone species. The truncation-induced aggregation of aSyn is toxic to neuronal culture, and inhibition of caspase-1 by shRNA or a specific chemical inhibitor improved the survival of a neuronal PD cell model. This study provides a molecular link for the role of inflammation in aSyn aggregation, and perhaps in the pathogenesis of sporadic PD as well.
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    Parkinson's disease-associated mutations in the GTPase domain of LRRK2 impair its nucleotide-dependent conformational dynamics
    (American Society for Biochemistry and Molecular Biology, 2019-04-12) Wu, Chun-Xiang; Liao, Jingling; Park, Yangshin; Reed, Xylena; Engel, Victoria A.; Hoang, Neo C.; Takagi, Yuichiro; Johnson, Steven M.; Wang, Mu; Federici, Mark; Nichols, R. Jeremy; Sanishvili, Ruslan; Cookson, Mark R.; Hoang, Quyen Q.; Biochemistry and Molecular Biology, School of Medicine
    Mutation in leucine-rich repeat kinase 2 (LRRK2) is a common cause of familial Parkinson's disease (PD). Recently, we showed that a disease-associated mutation R1441H rendered the GTPase domain of LRRK2 catalytically less active and thereby trapping it in a more persistently “on” conformation. However, the mechanism involved and characteristics of this on conformation remained unknown. Here, we report that the Ras of complex protein (ROC) domain of LRRK2 exists in a dynamic dimer–monomer equilibrium that is oppositely driven by GDP and GTP binding. We also observed that the PD-associated mutations at residue 1441 impair this dynamic and shift the conformation of ROC to a GTP-bound–like monomeric conformation. Moreover, we show that residue Arg-1441 is critical for regulating the conformational dynamics of ROC. In summary, our results reveal that the PD-associated substitutions at Arg-1441 of LRRK2 alter monomer–dimer dynamics and thereby trap its GTPase domain in an activated state.
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    A revised 1.6 Å structure of the GTPase domain of the Parkinson’s disease-associated protein LRRK2 provides insights into mechanisms
    (Cold Spring Harbor Laboratory Press, 2019) Wu, Chun-Xiang; Liao, Jingling; Park, Yangshin; Hoang, Neo C.; Engel, Victoria A.; Wan, Li; Oh, Misook; Sanishvili, Ruslan; Takagi, Yuichiro; Johnson, Steven M.; Wang, Mu; Federici, Mark; Nichols, R. Jeremy; Beilina, Alexandra; Reed, Xylena; Cookson, Mark R.; Hoang, Quyen Q.; Biochemistry and Molecular Biology, School of Medicine
    Leucine-rich repeat kinase 2 (LRRK2) is a large 286 kDa multi-domain protein whose mutation is a common cause of Parkinson’s disease (PD). One of the common sites of familial PD-associated mutations occurs at residue Arg-1441 in the GTPase domain of LRRK2. Previously, we reported that the PD-associated mutation R1441H impairs the catalytic activity of the GTPase domain thereby traps it in a persistently "on" state. More recently, we reported that the GTPase domain of LRRK2 exists in a dynamic dimer-monomer equilibrium where GTP binding shifts it to the monomeric conformation while GDP binding shifts it back to the dimeric state. We also reported that all of the PD-associated mutations at Arg-1441, including R1441H, R1441C, and R1441G, impair the nucleotide-dependent dimer-monomer conformational dynamics of the GTPase domain. However, the mechanism of this nucleotide-dependent conformational dynamics and how it is impaired by the mutations at residue Arg-1441 remained unclear. Here, we report a 1.6 Å crystal structure of the GTPase domain of LRRK2. Our structure has revealed a dynamic switch region that can be differentially regulated by GTP and GDP binding. This nucleotide-dependent regulation is impaired when residue Arg-1441 is substituted with the PD-associated mutations due to the loss of its exquisite interactions consisting of two hydrogen bonds and a π-stacking interaction at the dimer interface.
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    Structural and Biochemical Characterization of AidC, a Quorum-Quenching Lactonase With Atypical Selectivity
    (ACS, 2015-06) Mascarenhas, Romila; Thomas, Pei W.; Wu, Chun-Xiang; Nocek, Boguslaw P.; Hoang, Quyen Q.; Liu, Dali; Fast, Walter; Department of Biochemistry and Molecular Biology, IU School of Medicine
    Quorum-quenching catalysts are of interest for potential application as biochemical tools for interrogating interbacterial communication pathways, as antibiofouling agents, and as anti-infective agents in plants and animals. Herein, the structure and function of AidC, an N-acyl-l-homoserine lactone (AHL) lactonase from Chryseobacterium, is characterized. Steady-state kinetics show that zinc-supplemented AidC is the most efficient wild-type quorum-quenching enzymes characterized to date, with a kcat/KM value of approximately 2 × 106 M–1 s–1 for N-heptanoyl-l-homoserine lactone. The enzyme has stricter substrate selectivity and significantly lower KM values (ca. 50 μM for preferred substrates) compared to those of typical AHL lactonases (ca. >1 mM). X-ray crystal structures of AidC alone and with the product N-hexanoyl-l-homoserine were determined at resolutions of 1.09 and 1.67 Å, respectively. Each structure displays as a dimer, and dimeric oligiomerization was also observed in solution by size-exclusion chromatography coupled with multiangle light scattering. The structures reveal two atypical features as compared to previously characterized AHL lactonases: a “kinked” α-helix that forms part of a closed binding pocket that provides affinity and enforces selectivity for AHL substrates and an active-site His substitution that is usually found in a homologous family of phosphodiesterases. Implications for the catalytic mechanism of AHL lactonases are discussed.