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Le, Dung Tien,Lee, Byung Cheon,Marino, Stefano M.,Zhang, Yan,Fomenko, Dmitri E.,Kaya, Alaattin,Hacioglu, Elise,Kwak, Geun-Hee,Koc, Ahmet,Kim, Hwa-Young,Gladyshev, Vadim N. American Society for Biochemistry and Molecular Bi 2009 The Journal of biological chemistry Vol.284 No.7
<P>Methionine sulfoxide reductases (Msrs) are oxidoreductases that catalyze thiol-dependent reduction of oxidized methionines. MsrA and MsrB are the best known Msrs that repair methionine-S-sulfoxide (Met-S-SO) and methionine-R-sulfoxide (Met-R-SO) residues in proteins, respectively. In addition, an Escherichia coli enzyme specific for free Met-R-SO, designated fRMsr, was recently discovered. In this work, we carried out comparative genomic and experimental analyses to examine occurrence, evolution, and function of fRMsr. This protein is present in single copies and two mutually exclusive subtypes in about half of prokaryotes and unicellular eukaryotes but is missing in higher plants and animals. A Saccharomyces cerevisiae fRMsr homolog was found to reduce free Met-R-SO but not free Met-S-SO or dabsyl-Met-R-SO. fRMsr was responsible for growth of yeast cells on Met-R-SO, and the double fRMsr/MsrA mutant could not grow on a mixture of methionine sulfoxides. However, in the presence of methionine, even the triple fRMsr/MsrA/MsrB mutant was viable. In addition, fRMsr deletion strain showed an increased sensitivity to oxidative stress and a decreased life span, whereas overexpression of fRMsr conferred higher resistance to oxidants. Molecular modeling and cysteine residue targeting by thioredoxin pointed to Cys(101) as catalytic and Cys(125) as resolving residues in yeast fRMsr. These residues as well as a third Cys, resolving Cys(91), clustered in the structure, and each was required for the catalytic activity of the enzyme. The data show that fRMsr is the main enzyme responsible for the reduction of free Met-R-SO in S. cerevisiae.</P>
Le, Dung Tien,Lee, Hyun-Sook,Chung, Young-Je,Yoon, Moon-Young,Choi, Jung-Do Korean Chemical Society 2007 Bulletin of the Korean Chemical Society Vol.28 No.6
Mycobacterium tuberculosis is a pathogen responsible for 2-3 million deaths every year worldwide. The emergence of drug-resistant and multidrug-resistant tuberculosis has increased the need to identify new antituberculosis targets. Acetohydroxy acid synthase, (AHAS, EC 2.2.1.6), an enzyme involved in branched-chain amino acid synthesis, has recently been identified as a potential anti-tuberculosis target. To assist in the search for new inhibitors and “receptor-based” design of effective inhibitors of tubercular AHAS (TbAHAS), we constructed four different structural models of TbAHAS and used one of the models as a target for virtual screening of potential inhibitors. The quality of each model was assessed stereochemically by PROCHECK and found to be reliable. Up to 89% of the amino acid residues in the structural models were located in the most favored regions of the Ramachandran plot, which indicates that the conformation of each residue in the models is good. In the models, residues at the herbicide-binding site were highly conserved across 39 AHAS sequences. The binding mode of TbAHAS with a sulfonylurea herbicide was characterized by 32 hydrophobic interactions, the majority of which were contributed by residue Trp516. The model based on the highest resolution X-ray structure of yeast AHAS was used as the target for virtual screening of a chemical database containing 8300 molecules with a heterocyclic ring. We developed a short list of molecules that were predicted to bind with high scores to TbAHAS in a conformation similar to that of sulfonylurea derivatives. Five sulfonylurea herbicides that were calculated to efficiently bind TbAHAS were experimentally verified and found to inhibit enzyme activity at micromolar concentrations. The data suggest that this time-saving and costeffective computational approach can be used to discover new TbAHAS inhibitors. The list of chemicals studied in this work is supplied to facilitate independent experimental verification of the computational approach.
FAD-independent and Herbicide-resistant Mutants of Tobacco Acetohydroxy Acid Synthase
Le, Dung Tien,Choi, Jung-Do Korean Chemical Society 2005 Bulletin of the Korean Chemical Society Vol.26 No.6
Acetohydroxy acid synthase catalyzes the first common step in the biosynthesis of branched chain amino acids. AHAS plays two distinct metabolic roles, and is designated as anabolic AHAS and catabolic AHAS, depending on its function. Anabolic AHAS is FAD-dependent, while its catabolic counterpart is not. In this work, a conserved motif was identified in the $\beta$-domain of anabolic AHASs, but not in catabolic AHAS ($_{372}RFDDR_{376}$). In order to determine the functions of this motif, we replaced the motif with the corresponding sequence in FAD-independent AHAS, SPVEY. None of these three mutants (SPV, SPVE, and SPVEY) was detected with bound FAD. However, two of these mutants (SPVE and SPVEY) were active at a low level of specific activity. Although they exhibited pyruvate- and ThDP- dependent characteristics, the activity of the two active mutants appears to be FAD-independent. The SPVEY mutant was completely insensitive to the three tested herbicides, even at extremely high concentrations and is also somewhat more thermolabile than the wild type enzyme. The data provided in this work suggest that the RFDDR motif is a possible determinant of the FAD-dependent and herbicide-resistant properties of tobacco AHAS. The SPVEY mutant appears to exhibit catabolic AHAS-like activity.
Dung Tien Le,Nam Tuan Vu 한국응용생명화학회 2017 Applied Biological Chemistry (Appl Biol Chem) Vol.60 No.2
Effective disease management of crops is crucial to sustain food security and safeguard potential losses in crop production that worth billions of dollars. The key to success in plant disease management is having the ability to detect the causal pathogen(s) early and accurately. Polymerase chain reaction (PCR) has been a gold standard in nucleic acid-based diagnostics. Apart from PCR, within the last decade, the development of a technique called ‘‘loop-mediated isothermal amplification’’ or LAMP has facilitated the development of hundreds of simple assays for plant disease diagnostics. There are now more than 200 LAMP publications per year, of which 20% identify plant disease pathogens. Among them, LAMP assays are available for pathogen detection of 50 plant viruses, 20 bacterial plant diseases, 7 fungal plant diseases and several phytoplasmas. Here, we provide a comprehensive analysis of all LAMP assays available for detecting plant diseases, including various detection chemistries used. We also discuss how to avoid pitfalls when developing LAMP assays. Finally, we offer perspectives of the applications of LAMP in plant disease management, addressing the questions as to which extent the assays are helpful and whether they should be used outside the laboratory. This review will be a ‘‘handbook’’ for researchers developing LAMP assays for plant disease diagnostics.
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이진용(Tien Dung Le),강희준(Hee-Jun Kang) 제어로봇시스템학회 2012 제어·로봇·시스템학회 논문지 Vol.18 No.6
This paper describes the design of a fuzzy adaptive sliding mode controller for tracking control of robotic manipulators. The proposed controller incorporates a modified traditional sliding mode controller to drive the system state to a sliding surface and then keep the system state on this surface, and a fuzzy logic controller to accelerate the reaching phase. The stability of the control system is ensured by using Lyapunov theory. To verify the effectiveness of the proposed controller, computer simulation is conducted for a five-bar planar robotic manipulator. The simulation results show that the proposed controller can improve the reaching time and eliminate chattering of the control system at the same time.