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1.  Increased numbers of Foxp3-positive regulatory T cells in gastritis, peptic ulcer and gastric adenocarcinoma 
AIM: To determine the number of regulatory T cells (Tregs) in gastric mucosa of patients with gastritis, peptic ulcers and gastric cancer.
METHODS: This study was a retrospective analysis of gastric antrum biopsy specimens from healthy controls (n = 22) and patients with gastritis (n = 30), peptic ulcer (n = 83), or gastric cancer (n = 32). Expression of CD4, CD25 and Foxp3 was determined by immunohistochemistry in three consecutive sections per sample.
RESULTS: Compared with healthy controls, there was an increased number of CD25+ and Foxp3+ cells in patients with gastritis (P = 0.004 and P = 0.008), peptic ulcer (P < 0.001 and P < 0.001), and gastric cancer (P < 0.001 and P < 0.001). The ratio of CD25+/CD4+ or Foxp3+/CD4+ cells was also significantly higher in all disease groups (P < 0.001, respectively). The number of CD4+, CD25+, and Foxp3+ cells, and the ratio of CD25+/CD4+ and Foxp3+/CD4+ cells, were associated with the histological grade of the specimens, including acute inflammation, chronic inflammation, lymphoid follicle number, and Helicobacter pylori infection. The number of CD4+, CD25+ and Foxp3+ cells, and the ratio of CD25+/CD4+ and Foxp3+/CD4+ cells, were negatively associated with intestinal metaplasia among gastritis (P < 0.001, P < 0.001, P < 0.001, P = 0.002 and P = 0.002) and peptic ulcer groups (P = 0.013, P = 0.004, P < 0.001, P = 0.040 and P = 0.003).
CONCLUSION: Tregs are positively associated with endoscopic findings of gastroduodenal diseases and histological grade but negatively associated with intestinal metaplasia in gastritis and peptic ulcer groups.
PMCID: PMC3251803  PMID: 22228968
T regulatory cells; Helicobacter pylori; Gastroduodenal diseases; Intestinal metaplasia; Immunohistochemistry
2.  A local average distance descriptor for flexible protein structure comparison 
BMC Bioinformatics  2014;15:95.
Protein structures are flexible and often show conformational changes upon binding to other molecules to exert biological functions. As protein structures correlate with characteristic functions, structure comparison allows classification and prediction of proteins of undefined functions. However, most comparison methods treat proteins as rigid bodies and cannot retrieve similarities of proteins with large conformational changes effectively.
In this paper, we propose a novel descriptor, local average distance (LAD), based on either the geodesic distances (GDs) or Euclidean distances (EDs) for pairwise flexible protein structure comparison. The proposed method was compared with 7 structural alignment methods and 7 shape descriptors on two datasets comprising hinge bending motions from the MolMovDB, and the results have shown that our method outperformed all other methods regarding retrieving similar structures in terms of precision-recall curve, retrieval success rate, R-precision, mean average precision and F1-measure.
Both ED- and GD-based LAD descriptors are effective to search deformed structures and overcome the problems of self-connection caused by a large bending motion. We have also demonstrated that the ED-based LAD is more robust than the GD-based descriptor. The proposed algorithm provides an alternative approach for blasting structure database, discovering previously unknown conformational relationships, and reorganizing protein structure classification.
PMCID: PMC3992163  PMID: 24694083
3.  An improved ChIP-seq peak detection system for simultaneously identifying post-translational modified transcription factors by combinatorial fusion, using SUMOylation as an example 
BMC Genomics  2014;15(Suppl 1):S1.
Post-translational modification (PTM) of transcriptional factors and chromatin remodelling proteins is recognized as a major mechanism by which transcriptional regulation occurs. Chromatin immunoprecipitation (ChIP) in combination with high-throughput sequencing (ChIP-seq) is being applied as a gold standard when studying the genome-wide binding sites of transcription factor (TFs). This has greatly improved our understanding of protein-DNA interactions on a genomic-wide scale. However, current ChIP-seq peak calling tools are not sufficiently sensitive and are unable to simultaneously identify post-translational modified TFs based on ChIP-seq analysis; this is largely due to the wide-spread presence of multiple modified TFs. Using SUMO-1 modification as an example; we describe here an improved approach that allows the simultaneous identification of the particular genomic binding regions of all TFs with SUMO-1 modification.
Traditional peak calling methods are inadequate when identifying multiple TF binding sites that involve long genomic regions and therefore we designed a ChIP-seq processing pipeline for the detection of peaks via a combinatorial fusion method. Then, we annotate the peaks with known transcription factor binding sites (TFBS) using the Transfac Matrix Database (v7.0), which predicts potential SUMOylated TFs. Next, the peak calling result was further analyzed based on the promoter proximity, TFBS annotation, a literature review, and was validated by ChIP-real-time quantitative PCR (qPCR) and ChIP-reChIP real-time qPCR. The results show clearly that SUMOylated TFs are able to be pinpointed using our pipeline.
A methodology is presented that analyzes SUMO-1 ChIP-seq patterns and predicts related TFs. Our analysis uses three peak calling tools. The fusion of these different tools increases the precision of the peak calling results. TFBS annotation method is able to predict potential SUMOylated TFs. Here, we offer a new approach that enhances ChIP-seq data analysis and allows the identification of multiple SUMOylated TF binding sites simultaneously, which can then be utilized for other functional PTM binding site prediction in future.
PMCID: PMC4046823  PMID: 24564277
4.  Fermented Wheat Germ Extract Induced Cell Death and Enhanced Cytotoxicity of Cisplatin and 5-Fluorouracil on Human Hepatocellular Carcinoma Cells 
Hepatocellular carcinoma (HCC) is one of the most common causes of cancer-related death worldwide. Due to the difficulties of early diagnosis, curative treatments are not available for most patients. Palliative treatments such as chemotherapy are often associated with low response rate, strong adverse effects and limited clinical benefits for patients. The alternative approaches such as fermented wheat germ extract (FWGE) with anti-tumor efficacy may provide improvements in the clinical outcome of current therapy for HCC. This study aimed to clarify antitumor efficacy of FWGE and the combination drug effect of FWGE with chemotherapeutic agents, cisplatin and 5-fluorouracil (5-Fu) in human HCC cells, HepG2, Hep3B, and HepJ5. The present study indicated that FWGE exhibited potential to suppress HepG2, Hep3B, and HepJ5 cells, with the half maximal inhibitory concentrations (IC50) of FWGE were 0.494, 0.371 and 1.524 mg/mL, respectively. FWGE also induced Poly (Adenosine diphosphate ribose) polymerase (PARP) associated cell death in Hep3B cells. Moreover, the FWGE treatment further enhanced the cytotoxicity of cisplatin in all tested HCC cells, and cytotoxicity of 5-Fu in a synergistic manner in HepJ5 cells. Collectively, the results identified the anti-tumor efficacy of FWGE in HCC cells and suggested that FWGE can be used as a supplement to effectively improve the tumor suppression efficiency of cisplatin and 5-Fu in HCC cells.
PMCID: PMC3881523  PMID: 24454483
5.  Whole-Exome Sequencing to Identify a Novel LMNA Gene Mutation Associated with Inherited Cardiac Conduction Disease 
PLoS ONE  2013;8(12):e83322.
Inherited cardiac conduction diseases (CCD) are rare but are caused by mutations in a myriad of genes. Recently, whole-exome sequencing has successfully led to the identification of causal mutations for rare monogenic Mendelian diseases.
To investigate the genetic background of a family affected by inherited CCD.
Methods and Results
We used whole-exome sequencing to study a Chinese family with multiple family members affected by CCD. Using the pedigree information, we proposed a heterozygous missense mutation (c.G695T, Gly232Val) in the lamin A/C (LMNA) gene as a candidate mutation for susceptibility to CCD in this family. The mutation is novel and is expected to affect the conformation of the coiled-coil rod domain of LMNA according to a structural model prediction. Its pathogenicity in lamina instability was further verified by expressing the mutation in a cellular model.
Our results suggest that whole-exome sequencing is a feasible approach to identifying the candidate genes underlying inherited conduction diseases.
PMCID: PMC3861486  PMID: 24349489
6.  The chromatin modification by SUMO-2/3 but not SUMO-1 prevents the epigenetic activation of key immune-related genes during Kaposi’s sarcoma associated herpesvirus reactivation 
BMC Genomics  2013;14(1):824.
SUMOylation, as part of the epigenetic regulation of transcription, has been intensively studied in lower eukaryotes that contain only a single SUMO protein; however, the functions of SUMOylation during mammalian epigenetic transcriptional regulation are largely uncharacterized. Mammals express three major SUMO paralogues: SUMO-1, SUMO-2, and SUMO-3 (normally referred to as SUMO-1 and SUMO-2/3). Herpesviruses, including Kaposi’s sarcoma associated herpesvirus (KSHV), seem to have evolved mechanisms that directly or indirectly modulate the SUMO machinery in order to evade host immune surveillance, thus advancing their survival. Interestingly, KSHV encodes a SUMO E3 ligase, K-bZIP, with specificity toward SUMO-2/3 and is an excellent model for investigating the global functional differences between SUMO paralogues.
We investigated the effect of experimental herpesvirus reactivation in a KSHV infected B lymphoma cell line on genomic SUMO-1 and SUMO-2/3 binding profiles together with the potential role of chromatin SUMOylation in transcription regulation. This was carried out via high-throughput sequencing analysis. Interestingly, chromatin immunoprecipitation sequencing (ChIP-seq) experiments showed that KSHV reactivation is accompanied by a significant increase in SUMO-2/3 modification around promoter regions, but SUMO-1 enrichment was absent. Expression profiling revealed that the SUMO-2/3 targeted genes are primarily highly transcribed genes that show no expression changes during viral reactivation. Gene ontology analysis further showed that these genes are involved in cellular immune responses and cytokine signaling. High-throughput annotation of SUMO occupancy of transcription factor binding sites (TFBS) pinpointed the presence of three master regulators of immune responses, IRF-1, IRF-2, and IRF-7, as potential SUMO-2/3 targeted transcriptional factors after KSHV reactivation.
Our study is the first to identify differential genome-wide SUMO modifications between SUMO paralogues during herpesvirus reactivation. Our findings indicate that SUMO-2/3 modification near protein-coding gene promoters occurs in order to maintain host immune-related gene unaltered during viral reactivation.
PMCID: PMC4046822  PMID: 24267727
7.  Pathway-based Screening Strategy for Multitarget Inhibitors of Diverse Proteins in Metabolic Pathways 
PLoS Computational Biology  2013;9(7):e1003127.
Many virtual screening methods have been developed for identifying single-target inhibitors based on the strategy of “one–disease, one–target, one–drug”. The hit rates of these methods are often low because they cannot capture the features that play key roles in the biological functions of the target protein. Furthermore, single-target inhibitors are often susceptible to drug resistance and are ineffective for complex diseases such as cancers. Therefore, a new strategy is required for enriching the hit rate and identifying multitarget inhibitors. To address these issues, we propose the pathway-based screening strategy (called PathSiMMap) to derive binding mechanisms for increasing the hit rate and discovering multitarget inhibitors using site-moiety maps. This strategy simultaneously screens multiple target proteins in the same pathway; these proteins bind intermediates with common substructures. These proteins possess similar conserved binding environments (pathway anchors) when the product of one protein is the substrate of the next protein in the pathway despite their low sequence identity and structure similarity. We successfully discovered two multitarget inhibitors with IC50 of <10 µM for shikimate dehydrogenase and shikimate kinase in the shikimate pathway of Helicobacter pylori. Furthermore, we found two selective inhibitors (IC50 of <10 µM) for shikimate dehydrogenase using the specific anchors derived by our method. Our experimental results reveal that this strategy can enhance the hit rates and the pathway anchors are highly conserved and important for biological functions. We believe that our strategy provides a great value for elucidating protein binding mechanisms and discovering multitarget inhibitors.
Author Summary
Many drug development strategies focus on designing inhibitors for single targets. These inhibitors often lose potency owing to mutations in the protein binding sites and are ineffective for complex diseases. Multitarget inhibitors can decrease probability of drug resistance and enhance the therapeutic efficiency; however, identifying them is still a challenge because targets often have low sequence and structure similarities in their binding sites. Here we propose a pathway-based screening strategy that simultaneously screens proteins in a metabolic pathway for discovering multitarget inhibitors. Because these proteins interact with similar metabolites and modify them step-by-step, the proteins share similarities in binding sites. We developed pathway site-moiety maps that present the conserved binding environments of the proteins without relying on the sequence or structure alignment. Compounds that bind these conserved binding environments are often multitarget inhibitors. We applied this strategy to the shikimate pathway of Helicobacter pylori, and discovered two multitarget inhibitors (IC50<10 µM) for shikimate dehydrogenase and shikimate kinase. In addition, we found two selective inhibitors based on specific binding environments for shikimate dehydrogenase. Thus the pathway-based screening strategy is useful for identifying multitarget inhibitors and elucidating protein-ligand binding mechanisms and has the potential to be applied to human diseases.
PMCID: PMC3701698  PMID: 23861662
8.  Effects of Gender on Severity, Management and Outcome in Acute Biliary Pancreatitis 
PLoS ONE  2013;8(2):e57504.
We conducted a population-based cross-sectional study to examine gender differences in severity, management, and outcome among patients with acute biliary pancreatitis (ABP) because available data are insufficient and conflicting.
We analyzed 13,110 patients (50.6% male) with first-attack ABP from Taiwan’s National Health Insurance Research Database between 2000 and 2009. The primary outcome was hospital mortality. Secondary outcomes included the development of severe ABP and the provision of treatment measures. Gender difference was assessed using multivariable analyses with generalized estimating equations models.
The odds of gastrointestinal bleeding (adjusted odds ratio [aOR] 1.44, 95% confidence interval [CI] 1.18–1.76) and local complication (aOR 1.38, 95% CI 1.05–1.82) were 44% and 38% higher in men than in women, respectively. Compared with women, men had 24% higher odds of receiving total parenteral nutrition (aOR 1.24, 95% CI 1.00–1.52), but had 18% and 41% lower odds of receiving cholecystectomy (aOR 0.82, 95% CI 0.72–0.93) and hemodialysis (aOR 0.59, 95% CI 0.42–0.83), respectively. Hospital mortality was higher in men than in women (1.8% vs. 1.1%, p = 0.001). After adjustment for potential confounders, men had 81% higher odds of in-hospital death than women (aOR 1.81, 95% CI 1.15–2.86). Among patients with severe ABP, hospital mortality was 11.0% and 7.5% in men and women (p<0.001), respectively. The adjusted odds of death remained higher in men than in women with severe ABP (aOR 1.72, 95% CI 1.10–2.68).
Gender is an important determinant of outcome in patients with ABP and may affect their treatment measures.
PMCID: PMC3585306  PMID: 23469006
9.  Crystal Structures of Lysine-Preferred Racemases, the Non-Antibiotic Selectable Markers for Transgenic Plants 
PLoS ONE  2012;7(10):e48301.
Lysine racemase, a pyridoxal 5′-phosphate (PLP)-dependent amino acid racemase that catalyzes the interconversion of lysine enantiomers, is valuable to serve as a novel non-antibiotic selectable marker in the generation of transgenic plants. Here, we have determined the first crystal structure of a lysine racemase (Lyr) from Proteus mirabilis BCRC10725, which shows the highest activity toward lysine and weaker activity towards arginine. In addition, we establish the first broad-specificity amino acid racemase (Bar) structure from Pseudomonas putida DSM84, which presents not only the highest activity toward lysine but also remarkably broad substrate specificity. A complex structure of Bar-lysine is also established here. These structures demonstrate the similar fold of alanine racemase, which is a head-to-tail homodimer with each protomer containing an N-terminal (α/β)8 barrel and a C-terminal β-stranded domain. The active-site residues are located at the protomer interface that is a funnel-like cavity with two catalytic bases, one from each protomer, and the PLP binding site is at the bottom of this cavity. Structural comparisons, site-directed mutagenesis, kinetic, and modeling studies identify a conserved arginine and an adjacent conserved asparagine that fix the orientation of the PLP O3 atom in both structures and assist in the enzyme activity. Furthermore, side chains of two residues in α-helix 10 have been discovered to point toward the cavity and define the substrate specificity. Our results provide a structural foundation for the design of racemases with pre-determined substrate specificity and for the development of the non-antibiotic selection system in transgenic plants.
PMCID: PMC3485190  PMID: 23118975
10.  Protective effect of guggulsterone against cardiomyocyte injury induced by doxorubicin in vitro 
Doxorubicin (DOX) is an effective antineoplastic drug; however, clinical use of DOX is limited by its dose-dependent cardiotoxicity. It is well known that reactive oxygen species (ROS) play a vital role in the pathological process of DOX-induced cardiotoxicity. For this study, we evaluated the protective effects of guggulsterone (GS), a steroid obtained from myrrh, to determine its preliminary mechanisms in defending against DOX-induced cytotoxicity in H9C2 cells.
In this study, we used a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay, lactate dehydrogenase (LDH) release measurements, and Hoechst 33258 staining to evaluate the protective effect of GS against DOX-induced cytotoxicity in H9C2 cells. In addition, we observed the immunofluorescence of intracellular ROS and measured lipid peroxidation, caspase-3 activity, and apoptosis-related proteins by using Western blotting.
The MTT assay and LDH release showed that treatment using GS (1–30 μM) did not cause cytotoxicity. Furthermore, GS inhibited DOX (1 μM)-induced cytotoxicity in a concentration-dependent manner. Hoechst 33258 staining showed that GS significantly reduced DOX-induced apoptosis and cell death. Using GS at a dose of 10–30 μM significantly reduced intracellular ROS and the formation of MDA in the supernatant of DOX-treated H9C2 cells and suppressed caspase-3 activity to reference levels. In immunoblot analysis, pretreatment using GS significantly reversed DOX-induced decrease of PARP, caspase-3 and bcl-2, and increase of bax, cytochrome C release, cleaved-PARP and cleaved-caspase-3. In addition, the properties of DOX-induced cancer cell (DLD-1 cells) death did not interfere when combined GS and DOX.
These data provide considerable evidence that GS could serve as a novel cardioprotective agent against DOX-induced cardiotoxicity.
PMCID: PMC3493356  PMID: 22920231
Guggulsterone; Doxorubicin; Cardiotoxicity; Cytokines; Reactive oxygen species
11.  Structures of Helicobacter pylori Shikimate Kinase Reveal a Selective Inhibitor-Induced-Fit Mechanism 
PLoS ONE  2012;7(3):e33481.
Shikimate kinase (SK), which catalyzes the specific phosphorylation of the 3-hydroxyl group of shikimic acid in the presence of ATP, is the enzyme in the fifth step of the shikimate pathway for biosynthesis of aromatic amino acids. This pathway is present in bacteria, fungi, and plants but absent in mammals and therefore represents an attractive target pathway for the development of new antimicrobial agents, herbicides, and antiparasitic agents. Here we investigated the detailed structure–activity relationship of SK from Helicobacter pylori (HpSK). Site-directed mutagenesis and isothermal titration calorimetry studies revealed critical conserved residues (D33, F48, R57, R116, and R132) that interact with shikimate and are therefore involved in catalysis. Crystal structures of HpSK·SO4, R57A, and HpSK•shikimate-3-phosphate•ADP show a characteristic three-layer architecture and a conformationally elastic region consisting of F48, R57, R116, and R132, occupied by shikimate. The structure of the inhibitor complex, E114A•162535, was also determined, which revealed a dramatic shift in the elastic LID region and resulted in conformational locking into a distinctive form. These results reveal considerable insight into the active-site chemistry of SKs and a selective inhibitor-induced-fit mechanism.
PMCID: PMC3306394  PMID: 22438938
12.  Cholesterol Depletion Reduces Entry of Campylobacter jejuni Cytolethal Distending Toxin and Attenuates Intoxication of Host Cells ▿  
Infection and Immunity  2011;79(9):3563-3575.
Campylobacter jejuni is a common cause of pediatric diarrhea worldwide. Cytolethal distending toxin, produced by Campylobacter jejuni, is a putative virulence factor that induces cell cycle arrest and apoptosis in eukaryotic cells. Cellular cholesterol, a major component of lipid rafts, has a pivotal role in regulating signaling transduction and protein trafficking as well as pathogen internalization. In this study, we demonstrated that cell intoxication by Campylobacter jejuni cytolethal distending toxin is through the association of cytolethal distending toxin subunits and membrane cholesterol-rich microdomains. Cytolethal distending toxin subunits cofractionated with detergent-resistant membranes, while the distribution reduced upon the depletion of cholesterol, suggesting that cytolethal distending toxin subunits are associated with lipid rafts. The disruption of cholesterol using methyl-β-cyclodextrin not only reduced the binding activity of cytolethal distending toxin subunits on the cell membrane but also impaired their delivery and attenuated toxin-induced cell cycle arrest. Accordingly, cell intoxication by cytolethal distending toxin was restored by cholesterol replenishment. These findings suggest that membrane cholesterol plays a critical role in the Campylobacter jejuni cytolethal distending toxin-induced pathogenesis of host cells.
PMCID: PMC3165462  PMID: 21730089
13.  Core Site-Moiety Maps Reveal Inhibitors and Binding Mechanisms of Orthologous Proteins by Screening Compound Libraries 
PLoS ONE  2012;7(2):e32142.
Members of protein families often share conserved structural subsites for interaction with chemically similar moieties despite low sequence identity. We propose a core site-moiety map of multiple proteins (called CoreSiMMap) to discover inhibitors and mechanisms by profiling subsite-moiety interactions of immense screening compounds. The consensus anchor, the subsite-moiety interactions with statistical significance, of a CoreSiMMap can be regarded as a “hot spot” that represents the conserved binding environments involved in biological functions. Here, we derive the CoreSiMMap with six consensus anchors and identify six inhibitors (IC50<8.0 µM) of shikimate kinases (SKs) of Mycobacterium tuberculosis and Helicobacter pylori from the NCI database (236,962 compounds). Studies of site-directed mutagenesis and analogues reveal that these conserved interacting residues and moieties contribute to pocket-moiety interaction spots and biological functions. These results reveal that our multi-target screening strategy and the CoreSiMMap can increase the accuracy of screening in the identification of novel inhibitors and subsite-moiety environments for elucidating the binding mechanisms of targets.
PMCID: PMC3290551  PMID: 22393385
14.  Sacral herpes zoster presenting as sciatica 
PMCID: PMC2917966  PMID: 20501779
15.  SiMMap: a web server for inferring site-moiety map to recognize interaction preferences between protein pockets and compound moieties 
Nucleic Acids Research  2010;38(Web Server issue):W424-W430.
The protein–ligand interacting mechanism is essential to biological processes and drug discovery. The SiMMap server statistically derives site-moiety map with several anchors, which describe the relationship between the moiety preferences and physico-chemical properties of the binding site, from the interaction profiles between query target protein and its docked (or co-crystallized) compounds. Each anchor includes three basic elements: a binding pocket with conserved interacting residues, the moiety composition of query compounds and pocket–moiety interaction type (electrostatic, hydrogen bonding or van der Waals). We provide initial validation of the site-moiety map on three targets, thymidine kinase, and estrogen receptors of antagonists and agonists. Experimental results show that an anchor is often a hot spot and the site-moiety map can help to assemble potential leads by optimal steric, hydrogen bonding and electronic moieties. When a compound highly agrees with anchors of site-moiety map, this compound often activates or inhibits the target protein. We believe that the site-moiety map is useful for drug discovery and understanding biological mechanisms. The SiMMap web server is available at
PMCID: PMC2896162  PMID: 20519201
16.  Cholesterol Depletion Reduces Helicobacter pylori CagA Translocation and CagA-Induced Responses in AGS Cells▿  
Infection and Immunity  2008;76(7):3293-3303.
Infection with Helicobacter pylori cagA-positive strains is associated with gastritis, ulcerations, and gastric cancer. CagA is translocated into infected epithelial cells by a type IV secretion system and can be tyrosine phosphorylated, inducing signal transduction and motogenic responses in epithelial cells. Cellular cholesterol, a vital component of the membrane, contributes to membrane dynamics and functions and is important in VacA intoxication and phagocyte evasion during H. pylori infection. In this investigation, we showed that cholesterol extraction by methyl-β-cyclodextrin reduced the level of CagA translocation and phosphorylation. Confocal microscope visualization revealed that a significant portion of translocated CagA was colocalized with the raft marker GM1 and c-Src during infection. Moreover, GM1 was rapidly recruited into sites of bacterial attachment by live-cell imaging analysis. CagA and VacA were cofractionated with detergent-resistant membranes (DRMs), suggesting that the distribution of CagA and VacA is associated with rafts in infected cells. Upon cholesterol depletion, the distribution shifted to non-DRMs. Accordingly, the CagA-induced hummingbird phenotype and interleukin-8 induction were blocked by cholesterol depletion. Raft-disrupting agents did not influence bacterial adherence but did significantly reduce internalization activity in AGS cells. Together, these results suggest that delivery of CagA into epithelial cells by the bacterial type IV secretion system is mediated in a cholesterol-dependent manner.
PMCID: PMC2446742  PMID: 18443091
17.  Structural Basis for Shikimate-Binding Specificity of Helicobacter pylori Shikimate Kinase 
Journal of Bacteriology  2005;187(23):8156-8163.
Shikimate kinase (EC catalyzes the specific phosphorylation of the 3-hydroxyl group of shikimic acid in the presence of ATP. As the fifth key step in the shikimate pathway for aromatic amino acid biosynthesis in bacteria, fungi, and plants, but not mammals, shikimate kinase represents an attractive target for the development of new antimicrobial agents, herbicides, and antiparasitic agents. Here, we report the 1.8-Å crystal structure of Helicobacter pylori shikimate kinase (HpSK). The crystal structure shows a three-layer alpha/beta fold consisting of a central sheet of five parallel β-strands flanked by seven α-helices. An HpSK-shikimate-PO4 complex was also determined and refined to 2.3 Å, revealing induced-fit movement from an open to a closed form on substrate binding. Shikimate is located above a short 310 helix formed by a strictly conserved motif (GGGXV) after β3. Moreover, several highly conserved charged residues including Asp33 (in a conserved DT/SD motif), Arg57, and Arg132 (interacting with shikimate) are identified, guiding the development of novel inhibitors of shikimate kinase.
PMCID: PMC1291267  PMID: 16291688
18.  Engineering Streptomyces clavuligerus Deacetoxycephalosporin C Synthase for Optimal Ring Expansion Activity toward Penicillin G 
The deacetoxycephalosporin C synthase (DAOCS) from Streptomyces clavuligerus was engineered with the aim of enhancing the conversion of penicillin G into phenylacetyl-7-aminodeacetoxycephalosporanic acid, a precursor of 7-aminodeacetoxycephalosporanic acid, for industrial application. A single round of random mutagenesis followed by the screening of 5,500 clones identified three mutants, G79E, V275I, and C281Y, that showed a two- to sixfold increase in the kcat/Km ratio compared to the wild-type enzyme. Site-directed mutagenesis to modify residues surrounding the substrate resulted in three mutants, N304K, I305L, and I305M, with 6- to 14-fold-increased kcat/Km values. When mutants containing all possible combinations of these six sites were generated to optimize the ring expansion activity for penicillin G, the double mutant, YS67 (V275I, I305M), showed a significant 32-fold increase in the kcat/Km ratio and a 5-fold increase in relative activity for penicillin G, while the triple mutant, YS81 (V275I, C281Y, I305M), showed an even greater 13-fold increase in relative activity toward penicillin G. Our results demonstrate that this is a robust approach to the modification of DAOCS for an optimized DAOCS-penicillin G reaction.
PMCID: PMC154807  PMID: 12676714
19.  High Prevalence of cagA- and babA2-Positive Helicobacter pylori Clinical Isolates in Taiwan 
Journal of Clinical Microbiology  2002;40(10):3860-3862.
Two virulence markers, cagA and babA2, were characterized by PCR in 101 Helicobacter pylori isolates from a population in Taiwan. cagA was detected in 99% of the isolates, while babA2 was present in all of the isolates. Base deletions and substitutions at the forward babA2 primer annealing sites were found. Given their high prevalence, cagA and babA2 cannot be useful markers for predicting the high-risk patients of H. pylori infection in Taiwan.
PMCID: PMC130881  PMID: 12354901

Results 1-19 (19)