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  1. Jun 2019
    1. Electrostatic potentials were calculated by the Finite Difference Poisson-Boltzmann (FDPB) method using the program MEAD running within the PCE web server (http://bioserv.rpbs.jussieu.fr/PCE) (Miteva et al, 2005; Bashford et al, 1992). Additions of hydrogen atoms as well as assigning of atomic radii and charges were performed automatically within the server. MEAD numerically solves the Poisson-Boltzmann equation to yield the distribution of electrostatic potential on the protein surface. Calculations were performed on one of the native a-chains of the 2HbS crystal structure (Harrington et al, 1997) as well as its SCWRL (Dunbrack et al, 1993) generated mutants. All calculations were performed by setting the internal protein dielectric constant to 4 and the external solvent dielectric constant to 80. The ionic strength parameter was held at 0.1
    2. Electrostatic Potentia
  2. May 2019
    1. Cells growing in culture medium were harvested by trypsinization and washed twice with ice cold PBS. Cells were fixed by adding ice cold 70% ethanol and stored at 4°C. Before harvesting cells were washed twice with PBS and re-suspended in adequate amount of PBS containing Propidium Iodide (PI) to a final concentration of 50μg/ml and RNase to a final concentration of 10μg/ml. Thereby the cell suspension was incubated at 37°C for 30 minutes in dark. Analysis was done by running the samples in BD FACS Vantage System according to the standard procedures after calibration of instrument with Calibrite beads
    2. Flow Cytometry
    1. colonies come up after 48 hr. A freshly grown overnight culture of the TetR strain was washed once with an equal volume of citrate buffer and resuspended at 10- or 100-fold dilution in the same buffer. 0.1 ml aliquots were then spread on Maloy plates. Colonies were obtained at a frequency of ~ 4 x 10−5/plated cell. The colonies from the selection plate were purified on medium of the same composition and then scored for the Tets phenotype
    2. The method described by Maloy and Nunn (Maloy and Nunn, 1981) was followed for obtaining spontaneous TetS mutants of a TetR strain. Freshly grown cells of the TetR strain of O.D 0.7-0.8 was washed once with an equal volume of citrate buffer and resuspended at 10- or 100-fold dilution in the same buffer. 0.1 ml aliquots were then spread on Maloy agar plates and TetS colonies, which came up after 48 hr of incubation at 37 ̊C with a frequency of 5-8 big colonies/106-107 cells plated were purified on the same medium. This is not a clean selection since in a background lawn of slow growing TetR colonies, few faster growing TetS
    3. Selection for Tets colonies on medium described by Maloy et al
    1. Vacuolar morphology of C. glabratacells was examinedby staining vacuoleswith FM4-64 (Molecular Probes, Invitrogen). FM4-64 is a lipophilic dye that exhibits long wavelength red fluorescence when boundto lipids. FM4-64 binds to the plasma membrane and follows the endocytic pathway to reach the vacuole(Vida and Emr, 1995).Log-phase,YPDmedium-grown cells were harvested and washed with 1X PBS. 1 ODcells were resuspendedin 50 μl YPDmedium containing 30 μM FM4-64 andincubated at 30 ̊C for 30-45 min. After incubation, cells were washed thricewith YPD mediumand resuspendedin 100 μl of the samemedium. Cells were observed under confocal laser scanning microscope(Zeiss LSM 510 Meta)with 63X objective lens,2.5X final zoom, pinhole set at 108 μm and emission filterset to LP 565nmto capture fluorescence image.Along with the fluorescenceimage, aphase contrastimage was alsocaptured for each sample
    2. Staining of yeast vacuoleswith FM4-64
    1. QIAGEN QIAquick PCR purification kit containing buffers, spin columns and collection tubes wasused topurify DNA fragments from PCR andenzymatic digestion reactions as per the kit manufacturer’s instructions
    2. Purification of restriction enzyme-digestedand PCR amplifiedproducts
    3. E. coli BW23473 electro-competent cell aliquots were taken out from -70ºC freezer, thawed on ice and were mixed with 1-2 lplasmid DNA. Mixture was pulsed with the Gene Pulser® electroporation apparatus (Bio-Rad),set at 1800 Volts, 25 μF and 200 Ω,in a chilled 0.1 cm electroporation cuvette. After electric pulse, 1 ml LB medium was immediately added to the cuvette and suspension was transferred to a 1.5 ml sterile microcentrifuge tube. Cells were incubatedat 37°C and 200 rpm for 1 h, centrifuged and were plated on LB-agar plates containing kanamycin (30 μg/ml). Transformants were colony purifiedon LB-kanamycin plates. Positive clones were verified by colony PCR and inoculated in LB-liquid medium containing kanamycin (30 μg/ml) for plasmid isolation
    4. Transformation of E. coliBW23473 cells by electroporation
    1. The reaction was carried out by incubating at 37⁰C for 30 min. The reaction was stopped by adding 2μl of 0.5M EDTA, pH 8.0 and keeping on ice. A spin column was prepared using 1ml syringe and packed with sterile Sephadex G50 slurry and reaction mixture is applied on the top. The eluate is collected in different microcentrifuge tubes and radioactivity was counted using Geiger counter. The tube showing 7 to 9X106was used for experiment. The column containing the unincorporated [γ-32P] ATP was discarded in radioactive waste bin. The radiolabelled oligonucleotides were annealed with their corresponding complementary unlabelled oligonucleotides. A 50 fold molar excess of the latter was used for annealing for conversion of labelled single strand to double strand. Thetubes were kept in boiling waterbath for 3 min followed by room temperature for 30 min. The tubes were transferred to ice and the oligonucleotides were diluted to 4fmoles/μl using sterile H2O
    2. The oligonucleotides were labelled at their 5'end with 32P using T4 polynucleotide kinase (T4 PNK) enzyme in a reaction given belo
    3. end labelling of the oligonucleotides
    1. and stained with ‘Live & Dead’ cell assay reagent (5 μM ethidium homodimer, 5 μM calcein-AM) for 30 min at room temperature. Red (as dead) and green (as live) cells were analyzed under a fluorescence microscope (Labophot-2, Nikon, Tokyo, Japan).For flow cytometry, cells were transiently transfected with either empty vector or various constructs. After 12 h, cells were treated with a combination of CHX (cycloheximide, 25 μg/ml) and TNF (5 nM) for 24 h. Cells were washed, trypsinised and then subjectedto flow cytometry (FACS Aria, BD Biosciences) using Live-Dead Cytotoxicity assay kit (Invitrogen). Live versus dead cells were analysed using FlowJo software
    2. Cytotoxicity assay: The drug-induced cytotoxicity was measured by the 3-(4,5-Dimethylthiazolyl-2)-2,3-diphenyltetrazoliumbromide (MTT) assay as essentially described by Mosmann et al., 1983. Briefly, 5x104cells/well were seeded in 96-well plate. After 12 h, cells were treated in triplicates with different agents for different concentrations and time (in a final volume of 100μl). After completion of treatment, 25 μl of MTT solution (5 mg/ml in PBS) was then added and incubated for 2 h. The cytotoxicity was evaluated by uptake and cleavage of yellow MTT dye to purple formazan crystals by dehydrogenase activity in mitochondria of the living cells. Thereafter, 100 μl of extraction buffer (20% SDS in 50% dimethlylformamide) was added. After an overnight incubation at 37ºC, the absorbance at 570 nm was measured using 96-well multiscanner autoreader(Bio-Rad) with the extraction buffer as blank. Absorbance values were normalized to untreated cells and represented in percent cell viability for different concentrations or treatments.Determination of nuclear fragmentation: The morphology of live and dead cells was observed by staining the nucleus with DNA intercalating dye, propidium iodide (PI).Briefly, cells were treated with several apoptotic inducers for different concentration or time. Thereafter, cells werewashed with PBSand fixed in ice-cold 80% methanol for overnight at 4°C. Following day,cells were washed and suspended in 100 μl of PI solution (0.1% Triton, 0.2 mg/ml RNase A and 50 μg/ml PI in PBS) for 30 min in dark. Cells were then mounted on slides and viewed under fluorescence microscope (in 560 nm filter) to determine morphology of intact or fragmentednucleus.Live &dead assay: The cytotoxicity of various drugs was determined using the commercially available Live/Dead assay kit (Molecular Probes, Eugene, OR). Live cells have intact membraneand active cellular metabolism,which allow Calcien-AM to permeate inside and get cleaved into green fluorescent compound, Calcein (ex/em ~495 nm/~515 nm) due to intrinsic cellular esterase activity. On the other hand, Ethidium homodimer-1 (EthD-1) enters cells with damaged membranes and undergoes a 40-fold enhancement of fluorescence upon binding to nucleic acids, thereby producing a bright red fluorescence in dead cells (ex/em ~495 nm/~635 nm). Hence, the cell viability can be assayed by either flow cytometry or fluorescence microscopy.For imaging, cells with different drugs treatments were washed with PBS
    3. Assays for Apoptosis
    1. Yeast were grown in appropriate medium while the logarithmicphase and 1 OD600cells wereharvested and chilled on an ice(Elion and Warner, 1986). Allsubsequent steps,unless specified, werecarried out at4°C or on ice. Cells were collected by centrifugation at 2500 gfor 6min and washed with2 mLof TMN (Section Cells were suspended in 1 mL of ice cold permeabilization buffer (Section and incubated for 15 min.Cells were pelleted and incubated with 100μLof transcription assay buffer (Section containingradiolabelled [α-32P]UTP. After incubation for 10 min at30°C and 300 rpm in a shaking drybath (Eppendorf),1mLof cold TMN containing1 mM nonradioactive UTP was added, the cells were collected by centrifugation, and RNA was prepared by the hot phenol methodas described in Section 2.2.8. Equal counts of labelled RNA were used for hybridization. The membrane was pre incubated with 50 mL of hybridization buffer for 20-30 min, and hybridization was performed with labelled RNA at 65°C for 15 h in 20 mL of hybridization buffer
    2. Transcription run on analysis
    1. immunoprecipitation by using substrate specific antibody or pull-down by affinity trapping the substrate tag. The IP/pull-down complexes wereanalyzed by detecting the ubiquitination of substrate protein by using either substrate specificantibody or ubiquitin antibody through western blotting
    2. HeLa cells were transfected with various combinations of plasmids. At 24 h post-transfection, cells were treated with MG132 (10μM) for 6 h and the whole-cell extracts were prepared by NETN lysis. The cell lysatewas subjected to
    3. In vivoubiquitylation assay
    1. 2 bed volumes of methanol, and equilibrated with 5 bed volumes of distilled water. In order to reduce the water solubility of siderophore in the supernatant, it was acidified to pH 2 using concentarted HCl. This acidified supernatant was passsed through the column, and finally eluted with 160 ml methanol by collecting approximately 60 fractions (2 ml each) of the flow through. Siderophore assay was done on CAS plate with each collected fraction. Fraction that gave orangish-yellow halo for the siderophore on CAS plate, was combined together, dried in rotary evaporator and finally reconstituted in 1 ml methanol for further quantification using HPLC as described previously (Amin et al., 2009).For HPLC analysis, siderophore samples were filtered through filter membrane (porosity, 0.45 μ). Next, 10 μl sample was injected into Agilent C18 (4.6mm×250mm×5μm) column (gradient:(A=H2O/0.1%TFA), (B= CH3CN/0.1%TFA) 0-30% B in 10 min, 30-45% B in 15 min,45-0%B in 20 min at a flow rate of 1 ml/min). Similarly, standard vibrioferrin (siderophore produced by Xanthomonas) was also estimated through HPLC for comparison. Fe(III) bound vibrioferrin complex was prepared by incubating FeCl3.6H2O and apo-vibrioferrin for overnight. This complex was detected at300 nm (RT 10.998 min), whereas apo-vibrioferrin was detected at 220 nm at RT 10.988 min. The siderophore concentration in the samples were determined by peak area and calculated against the standard curves obtained from standard vibrioferrin. The siderophore from the test samples were detected at 300 nm, which confirms that majority of the vibrioferrin isolated from the culture was present in bound form
    2. Different Xanthomonas oryzaepv. oryzicola strains were grown overnight in PS medium at 28 °C and 200 rpm. 0.2% of the overnight grown culture was inoculated in the the fresh PS medium supplemented with 50 μM 2, 2’-dipyridyl, and grown till OD600 reached to 1. Cultures were centrifuged at 12,000 g for 50 min to get the cell free culture supernantant, which was collected into acid treated bottles. Excess exoplysaccharide was removed by centrifugation for longer time. Siderophore was initially isolated by column chromatography as described previously (Wright, 2010). Briefly, 220 g of XAD-16 resin was soaked overnight and packed into the column (2.4×30 cm), column was wa
    3. HPLC based siderophore estimation from culture supernatant of different strains of X. oryzaepv. oryzicola
    1. Cells were seeded in six well plates. After attaining optimal growth, cell lysates were prepared by scraping cells in 1x Laemmli buffer and samples were processed by standard western blot techniques. To detect FAKactivation samples were processed as described in Section 2.2.13. Briefly, 2 x106cells (6 x105cells per time point) were held in suspensionin complete medium containing 1% methylcellulosefor 90 min (Susp), andreplatedon fibronectin (2 μg/mL) coated surfacesfor 20 min (+FN)or for 4 h (SA -stably adherent). Cells at each time point were lysed in 1x Laemmli buffer and subjected to immunoblotting. Membranes were probed with specific antibodies(Table 2.3)and detected using the ECL detection system (GE Healthcare) as described in Section 2.2.10
    2. Immunoblot analysis to detect pFAK