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Search Results: 1 - 10 of 4556 matches for " Nam-Chul Ha "
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Interaction Mediated by the Putative Tip Regions of MdsA and MdsC in the Formation of a Salmonella-Specific Tripartite Efflux Pump
Saemee Song, Soonhye Hwang, Seunghwa Lee, Nam-Chul Ha, Kangseok Lee
PLOS ONE , 2014, DOI: 10.1371/journal.pone.0100881
Abstract: To survive in the presence of a wide range of toxic compounds, gram-negative bacteria expel such compounds via tripartite efflux pumps that span both the inner and outer membranes. The Salmonella-specific MdsAB pump consists of MdsB, a resistance-nodulation-division (RND)-type inner membrane transporter (IMT) that requires the membrane fusion protein (MFP) MdsA, and an outer membrane protein (OMP; MdsC or TolC) to form a tripartite efflux complex. In this study, we investigated the role of the putative tip regions of MdsA and its OMPs, MdsC and TolC, in the formation of a functional MdsAB-mediated efflux pump. Comparative analysis indicated that although sequence homologies of MdsA and MdsC with other MFPs and OMPs, respectively, are extremely low, key residues in the putative tip regions of these proteins are well conserved. Mutagenesis studies on these conserved sites demonstrated their importance for the physical and functional interactions required to form an MdsAB-mediated pump. Our studies suggest that, despite differences in the primary amino acid sequences and functions of various OMPs and MFPs, interactions mediated by the conserved tip regions of OMP and MFP are required for the formation of functional tripartite efflux pumps in gram-negative bacteria.
Membrane Fusion Proteins of Type I Secretion System and Tripartite Efflux Pumps Share a Binding Motif for TolC in Gram-Negative Bacteria
Minho Lee, So-Young Jun, Bo-Young Yoon, Saemee Song, Kangseok Lee, Nam-Chul Ha
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0040460
Abstract: The Hly translocator complex of Escherichia coli catalyzes type I secretion of the toxin hemolysin A (HlyA). In this complex, HlyB is an inner membrane ABC (ATP Binding Cassette)-type transporter, TolC is an outer membrane channel protein, and HlyD is a periplasmic adaptor anchored in the inner membrane that bridges HlyB to TolC. This tripartite organization is reminiscent of that of drug efflux systems such as AcrA-AcrB-TolC and MacA-MacB-TolC of E. coli. We have previously shown the crucial role of conserved residues located at the hairpin tip region of AcrA and MacA adaptors during assembly of their cognate systems. In this study, we investigated the role of the putative tip region of HlyD using HlyD mutants with single amino acid substitutions at the conserved positions. In vivo and in vitro data show that all mutations abolished HlyD binding to TolC and resulted in the absence of HlyA secretion. Together, our results suggest that, similarly to AcrA and MacA, HlyD interacts with TolC in a tip-to-tip manner. A general model in which these conserved interactions induce opening of TolC during drug efflux and type I secretion is discussed.
Modulation of RNase E Activity by Alternative RNA Binding Sites
Daeyoung Kim, Saemee Song, Minho Lee, Hayoung Go, Eunkyoung Shin, Ji-Hyun Yeom, Nam-Chul Ha, Kangseok Lee, Yong-Hak Kim
PLOS ONE , 2014, DOI: 10.1371/journal.pone.0090610
Abstract: Endoribonuclease E (RNase E) affects the composition and balance of the RNA population in Escherichia coli via degradation and processing of RNAs. In this study, we investigated the regulatory effects of an RNA binding site between amino acid residues 25 and 36 (24LYDLDIESPGHEQK37) of RNase E. Tandem mass spectrometry analysis of the N-terminal catalytic domain of RNase E (N-Rne) that was UV crosslinked with a 5′-32P-end-labeled, 13-nt oligoribonucleotide (p-BR13) containing the RNase E cleavage site of RNA I revealed that two amino acid residues, Y25 and Q36, were bound to the cytosine and adenine of BR13, respectively. Based on these results, the Y25A N-Rne mutant was constructed, and was found to be hypoactive in comparison to wild-type and hyperactive Q36R mutant proteins. Mass spectrometry analysis showed that Y25A and Q36R mutations abolished the RNA binding to the uncompetitive inhibition site of RNase E. The Y25A mutation increased the RNA binding to the multimer formation interface between amino acid residues 427 and 433 (427LIEEEALK433), whereas the Q36R mutation enhanced the RNA binding to the catalytic site of the enzyme (65HGFLPL*K71). Electrophoretic mobility shift assays showed that the stable RNA-protein complex formation was positively correlated with the extent of RNA binding to the catalytic site and ribonucleolytic activity of the N-Rne proteins. These mutations exerted similar effects on the ribonucleolytic activity of the full-length RNase E in vivo. Our findings indicate that RNase E has two alternative RNA binding sites for modulating RNA binding to the catalytic site and the formation of a functional catalytic unit.
Direct Inhibition of GSK3β by the Phosphorylated Cytoplasmic Domain of LRP6 in Wnt/β-Catenin Signaling
Shunfu Piao, Sun-Hye Lee, Hyunjoon Kim, Soohwan Yum, Jennifer L. Stamos, Yongbin Xu, Su-Jin Lee, Jaewon Lee, Sangtaek Oh, Jin-Kwan Han, Bum-Joon Park, William I. Weis, Nam-Chul Ha
PLOS ONE , 2008, DOI: 10.1371/journal.pone.0004046
Abstract: Wnt/β-catenin signaling plays a central role in development and is also involved in a diverse array of diseases. Binding of Wnts to the coreceptors Frizzled and LRP6/5 leads to phosphorylation of PPPSPxS motifs in the LRP6/5 intracellular region and the inhibition of GSK3β bound to the scaffold protein Axin. However, it remains unknown how GSK3β is specifically inhibited upon Wnt stimulation. Here, we show that overexpression of the intracellular region of LRP6 containing a Ser/Thr rich cluster and a PPPSPxS motif impairs the activity of GSK3β in cells. Synthetic peptides containing the PPPSPxS motif strongly inhibit GSK3β in vitro only when they are phosphorylated. Microinjection of these peptides into Xenopus embryos confirms that the phosphorylated PPPSPxS motif potentiates Wnt-induced second body axis formation. In addition, we show that the Ser/Thr rich cluster of LRP6 plays an important role in LRP6 binding to GSK3β. These observations demonstrate that phosphorylated LRP6/5 both recruits and directly inhibits GSK3β using two distinct portions of its cytoplasmic sequence, and suggest a novel mechanism of activation in this signaling pathway.
catena-Poly[hemi(hexane-1,6-diammonium) [[aquadibromidomanganese(II)]-μ-pyridine-2-carboxylato]]
Nam-Ho Kim,In-Chul Hwang,Kwang Ha
Acta Crystallographica Section E , 2009, DOI: 10.1107/s1600536809016316
Abstract: The asymmetric unit of the title compound, {(C6H18N2)0.5[MnBr2(C6H4NO2)(H2O)]}n, contains the repeat unit of the complex anion and one-half of a hexane-1,6-diammonium cation that is located on a twofold rotation axis. In the anionic polymer, the Mn2+ ions are bridged by the pyridinecarboxylate (pic) anion ligand, forming a chain structure along the c axis. The Mn2+ ion is six-coordinated in a distorted octahedral environment by one N atom of the pyridine ring, two O atoms of the two carboxylate groups, one O atom of the water molecule and two Br atoms. The compound displays intermolecular N—H...O, N—H...Br, O—H...Br and O—H...O hydrogen bonding. There may also be intermolecular π–π interactions between adjacent pyridine rings, with a centroid–centroid distance of 3.992 (4) .
Dichloridobis(pyridine-2-carboxylato-κ2N,O)platinum(IV) acetonitrile solvate
Nam-Ho Kim,In-Chul Hwang,Kwang Ha
Acta Crystallographica Section E , 2009, DOI: 10.1107/s1600536809017966
Abstract: The asymmetric unit of the title compound, [PtCl2(C6H4NO2)2]·CH3CN, contains a neutral PtIV complex and an acetonitrile solvent molecule. In the complex, the Pt4+ atom is six-coordinated in a distorted octahedral environment by two N atoms and two O atoms from two pyridinecarboxylate (pic) ligands and two Cl atoms. The Cl atoms are cis with respect to each other. The compound displays inter- and intramolecular C—H...O and C—H...Cl hydrogen bonding.
Redetermination of (2,2′-bipyridine-κ2N,N′)dichloridopalladium(II) dichloromethane solvate
Nam-Ho Kim,In-Chul Hwang,Kwang Ha
Acta Crystallographica Section E , 2009, DOI: 10.1107/s1600536809016262
Abstract: In the title compound, [PdCl2(C10H8N2)]·CH2Cl2, the Pd2+ ion is four-coordinated in a slightly distorted square-planar environment by two N atoms of the 2,2′-bipyridine (bipy) ligand and two chloride ions. The compound displays intramolecular C—H...Cl hydrogen bonds and pairs of complex molecules are connected by intermolecular C—H...Cl hydrogen bonds. Intermolecular π–π interactions are present between the pyridine rings of the ligand, the shortest centroid–centroid distance being 4.096 (3) . As a result of the electronic nature of the chelate ring, it is possible to create π–π interactions to its symmetry-related counterpart [3.720 (2) ] and also with a pyridine ring [3.570 (3) ] of the bipy unit. The present structure is a redetermination of a previous structure [Vicente et al. (1997). Private communication (refcode PYCXMN02). CCDC, Cambridge, England]. In the new structure refinement all H atoms were located in a difference Fourier synthesis. Their coordinates were refined freely, together with isotropic displacement parameters.
[μ-N,N,N′,N′-Tetrakis(2-pyridylmethyl)hexane-1,6-diamine]bis[dichloridomanganese(II)]
In-Chul Hwang,Nam-Ho Kim,Kwang Ha
Acta Crystallographica Section E , 2009, DOI: 10.1107/s1600536809003663
Abstract: The asymmetric unit of the title compound, [Mn2Cl4(C30H36N6)], contains one-half of the formula unit; a centre of inversion is located at the mid-point of the molecule. The two Mn2+ ions are bridged by the dual tridentate N,N,N′,N′-tetrakis(2-pyridylmethyl)hexane-1,6-diamine ligand to form a dinuclear complex. Each Mn atom is five-coordinated in an approximately square-pyramidal geometry by three N atoms from the ligand and two Cl atoms. Intermolecular π–π interactions between adjacent pyridine rings with a centroid–centroid distance of 3.576 (2) are reported.
Bis(2,2′-bipyridine-κ2N,N′)dichloridoplatinum(IV) dichloride monohydrate
Nam-Ho Kim,In-Chul Hwang,Kwang Ha
Acta Crystallographica Section E , 2009, DOI: 10.1107/s1600536809000725
Abstract: In the title complex, [PtCl2(C10H8N2)2]Cl2·H2O, the Pt4+ ion is six-coordinated in a distorted octahedral environment by four N atoms from the two 2,2′-bipyridine ligands and two Cl atoms. As a result of the different trans influences of the N and Cl atoms, the Pt—N bonds trans to the Cl atom are slightly longer than those trans to the N atom. The compound displays intermolecular hydrogen bonding between the water molecule and the Cl anions. There are intermolecular π–π interactions between adjacent pyridine rings, with a centroid–centroid distance of 3.962 .
Tetrachlorido(1,10-phenanthroline-κ2N,N′)platinum(IV) acetonitrile hemisolvate
Nam-Ho Kim,In-Chul Hwang,Kwang Ha
Acta Crystallographica Section E , 2009, DOI: 10.1107/s1600536809002359
Abstract: The asymmetric unit of the title compound, [PtCl4(C12H8N2)]·0.5CH3CN, contains two crystallographically independent PtIV complexes with very similar geometry and one solvent molecule. In the complexes, each PtIV ion is six-coordinated in a distorted octahedral environment by two N atoms of the 1,10-phenanthroline ligand and four Cl atoms. Because of the different trans effects of the N and Cl atoms, the Pt—Cl bonds trans to the N atom are slightly shorter than those trans to the Cl atom. The compound displays numerous intermolecular π–π interactions between six-membered rings, with a shortest centroid-to-centroid distance of 3.654 . There are also weak intra- and intermolecular C—H...Cl hydrogen bonds.
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