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Biomedical subjects

J K Ghosh

Publications and source records attributed to J K Ghosh.

16 recordsLinked to original sources
PubMed2003

Studies on the aggregation and possible channel formation in membranes of a cyclic hexapeptide, cyclo (D-Ala-L-Pro-L-Ala)2.

The interaction of zwitterionic lipid DMPC and DPPC with cyclic hexapeptide, cyclo (D-Ala-L-Pro-L-Ala)2 was studied using circular dichroism (CD) and differential scanning calorimetry (DSC). Preliminary membrane conductance results showed that the peptide has a tendency to form channels inside the lipid bilayer. CD studies indicated that as the lipid/peptide (L/P) ratio (DMPC/peptide) was increased, the magnitude of the negative CD band having a lambda(max) around 200 nm decreased. At a L/P ratio of 210:1, this band disappeared completely, indicating dramatic conformational changes in the peptide on interaction with the lipid bilayer. Reduction of the phase transition temperature and the maximum heat capacity of the lipid bilayer (DPPC) for gel-to-liquid crystalline phase transition indicates a strong interaction of the peptide with the lipid bilayer.

Biological Transport↗
PubMed2002

Variable selection in high-dimensional multivariate binary data with application to the analysis of microbial community DNA fingerprints.

In order to understand the relevance of microbial communities on crop productivity, the identification and characterization of the rhizosphere soil microbial community is necessary. Characteristic profiles of the microbial communities are obtained by denaturing gradient gel electrophoresis (DGGE) of polymerase chain reaction (PCR) amplified 16S rDNA from soil extracted DNA. These characteristic profiles, commonly called community DNA fingerprints, can be represented in the form of high-dimensional binary vectors. We address the problem of modeling and variable selection in high-dimensional multivariate binary data and present an application of our methodology in the context of a controlled agricultural experiment.

Agriculture↗
PubMed2001

Induction of a diverse T cell receptor gamma/delta repertoire by the helix-loop-helix proteins E2A and HEB in nonlymphoid cells.

During specific stages of thymocyte development, the T cell receptor (TCR) locus is assembled from variable (V), diversity (D), and joining (J) gene segments. Proper TCR gamma and delta V(D)J rearrangement during thymocyte development requires the presence of the E2A proteins. Here we show that E2A and a closely related protein, HEB, in the presence of recombination activating gene (RAG)1 and RAG2, each have the ability to activate TCR gamma and delta rearrangement in human kidney cells. The coding joints are diverse, contain nucleotide deletions, and occasionally show the presence of P nucleotides. Interestingly, only a subset of V, D, and J segments are targeted by the E2A and HEB proteins. Thus, E2A and HEB permit localized accessibility of the TCR gamma and delta loci to the recombination machinery. These data indicate that a distinct but diverse TCR repertoire can be induced in nonlymphoid cells by the mere presence of the V(D)J recombinase and the transcriptional regulators, E2A and HEB.

Basic Helix-Loop-Helix Proteins↗
PubMed2001

Rapid non-destructive quantitative estimation of urania/thoria in mixed thorium uranium di-oxide pellets by high-resolution gamma-ray spectrometry.

A non-destructive technique using high-resolution gamma-ray spectrometry has been standardised for quantitative estimation of uranium/thorium in mixed (ThO2-UO2) fuel pellets of varying composition. Four gamma energies were selected; two each from the uranium and thorium series and the time of counting has been optimised. This technique can be used for rapid estimation of U/Th percentage in a large number of mixed fuel pellets from a production campaign.

Radiation Monitoring↗
PubMed2000

Sendai virus internal fusion peptide: structural and functional characterization and a plausible mode of viral entry inhibition.

Viral glycoproteins catalyze the fusion between viral and cellular membranes. The fusion protein (F(1)) of Sendai virus has two fusion peptides. One is located at its N-terminus and the other, highly homologous to the HIV-1 and RSV fusion peptides, in the interior of the F(1) protein. A synthetic peptide corresponding to the internal fusogenic domain, namely, SV-201, was found to inhibit virus-cell fusion without interfering with the binding of the virus to the target cells, thus highlighting the importance of this region in Sendai virus-induced membrane fusion. However, its detailed mechanism of inhibition remains unknown. Here, we synthesized a shorter version of SV-201, namely, SV-208, an elongated one, SV-197, and two mutants of SV-201, and compared them functionally and structurally with SV-201. In contrast to SV-201, SV-208 and the two mutants do not inhibit virus-cell fusion. The differences in the oligomerization state of these peptides in aqueous solution and within the membrane, and in their ability to bind to Sendai virions, enabled us to postulate a possible mechanism of viral entry inhibition: SV-201 binds to its target in Sendai virions before the F(1) internal fusion peptide binds to the membrane, therefore blocking the F(1) conformational change required for fusion. In addition, we further characterized the fusogenic activity of the internal fusion peptide, compared to the N-terminal one, and determined its structure in the membrane-bound state by means of fluorescence, CD, and ATR-FTIR spectroscopy. Remarkably, we found that SV-201 and its elongated form, SV-197, are highly potent in inducing fusion of the highly stable large unilamellar vesicles composed of egg phosphatidylcholine, a property found only in an extended version of the HIV-1 fusion peptide. The inhibitory activity of SV-201 and its fusogenic ability are discussed in terms of the "umbrella" model of Sendai virus-induced membrane fusion.

Amino Acid Sequence↗
PubMed1999

Direct evidence that the N-terminal heptad repeat of Sendai virus fusion protein participates in membrane fusion.

Recent studies have demonstrated the importance of heptad repeat regions within envelope proteins of viruses in mediating conformational changes at various stages of viral infection. However, it is not clear if heptad repeats have a direct role in the actual fusion event. Here we have synthesized, fluorescently labeled and functionally and structurally characterized a wild-type 70 residue peptide (SV-117) composed of both the fusion peptide and the N-terminal heptad repeat of Sendai virus fusion protein, two of its mutants, as well as the fusion peptide and heptad repeat separately. One mutation was introduced in the fusion peptide (G119K) and another in the heptad repeat region (I154K). Similar mutations have been shown to drastically reduce the fusogenic ability of the homologous fusion protein of Newcastle disease virus. We found that only SV-117 was active in inducing lipid mixing of egg phosphatidylcholine/phosphatidyiglycerol (PC/PG) large unilamellar vesicles (LUV), and not the mutants nor the mixture of the fusion peptide and the heptad repeat. Functional characterization revealed that SV-117, and to a lesser extent its two mutants, were potent inhibitors of Sendai virus-mediated hemolysis of red blood cells, while the fusion peptide and SV-150 were negligibly active alone or in a mixture. Hemagglutinin assays revealed that none of the peptides disturb the binding of virions to red blood cells. Further studies revealed that SV-117 and its mutants oligomerize similarly in solution and in membrane, and have similar potency in inducing vesicle aggregation. Circular dichroism and FTIR spectroscopy revealed a higher helical content for SV-117 compared to its mutants in 40 % tifluorethanol and in PC/PG multibilayer membranes, respectively, ATR-FTIR studies indicated that SV-117 lies more parallel with the surface of the membrane than its mutants. These observations suggest a direct role for the N-terminal heptad repeat in assisting the fusion peptide in mediating membrane fusion.

Amino Acid Sequence↗
PubMed1998

Structure-function study of a heptad repeat positioned near the transmembrane domain of Sendai virus fusion protein which blocks virus-cell fusion.

A synthetic heptad repeat, SV-473, derived from Sendai virus fusion protein is a potent inhibitor of virus-cell fusion. In order to understand the mechanism of the inhibitory effect, we synthesized and fluorescently labeled SV-465, an extended version of SV-473 by one more heptad, its mutant peptide A17,24-SV-465, in which two heptadic leucines were substituted with two alanines, and its enatiomer D-SV-465, composed entirely of Damino acids. Similar mutations in the homologous fusion protein of the Newcastle disease virus drastically reduced its activity. The data revealed that SV-465, but not A17,24-SV-465 or its enantiomer, is highly active in inhibiting Sendai virus-induced hemolysis of red blood cells. None of the peptides interfere with the binding of virions to the target red blood cells as demonstrated by hemagglutinin assay. Fluorescence and circular dichroism (CD) spectroscopy indicated that: (i) only SV-465 could self-assemble in aqueous environment; (ii) only SV-465 could co-assemble with two other biologically active heptad repeats derived from Sendai virus fusion protein; (iii) SV-465 has a higher helical content than A17,24-SV-465 in solution, and (iv) all the peptides bind strongly to zwitterionic and negatively charged phospholipids. Polarized attenuated total reflection infrared spectroscopy revealed that they bound as monomers onto the surface of zwitterionic membranes with predominantly alpha-helical structures. The functional role of the amino acid 465-497 domain in Sendai virus-mediated membrane fusion is discussed in light of these findings.

Amino Acid Sequence↗
PubMed1998

A peptide derived from a conserved domain of Sendai virus fusion protein inhibits virus-cell fusion. A plausible mode of action.

SV-201, a peptide derived from a conserved and potentially amphipathic region (amino acids 201-229) in the Sendai virus ectodomain, specifically inhibited virus-mediated hemolysis only when added to virions prior to their attachment to red blood cells. Sendai virus-mediated hemagglutinin assay in the presence of SV-201 demonstrated that the peptide does not disturb the binding of virions to the target red blood cells. A mutated peptide with 2 amino acids substitution, rendering the peptide neutral, was biologically inactive. A second mutant with 7 amino acids randomized at the N terminus keeping the hydrophobicity of the peptide unaltered was only slightly active. A hydrophobic peptide corresponding to the fusion peptide domain was also inactive. SV-201, the two mutants, and the fusion peptide bind similarly with high affinity to both negatively charged phosphatidylserine/phosphatidylcholine and zwitterionic phosphatidylcholine lipid vesicles, suggesting that the inhibitory effect is not due merely to membrane modulation. Fluorescence studies with rhodamine-labeled peptides and SV-201-induced inhibition assays, demonstrated that the SV-201 binding site is most probably located in the region corresponding to amino acids 201-229 of the Sendai virus fusion protein. The data presented here suggest that SV-201 disturbs a functional domain in the Sendai virus fusion protein, which is most probably associated with the assembly of the fusion protein and/or membrane apposition. The existence of homologous SV-201 regions in other viruses suggests that these regions may have a similar role, and their synthetic counterparts may act as inhibitors for the corresponding viruses.

Amino Acid Sequence↗
PubMed1998

Spectroscopic studies of the interactions of the pyrethroid insecticide fenvalerate with gramicidin.

Fenvalerate is a pyrethroid insecticide which interacts with ionic channels. Using circular dichroism technique we have studied the interaction of fenvalerate with gramicidin, a model channel peptide which transports ions. In most organic solvents, gramicidin exists as a double helix except in trifluoroethanol where it exists as a channel forming single stranded beta6.3 helical monomer. In model lipid membranes, under certain experimental conditions, gramicidin exists as a channel forming single stranded beta6.3 helical dimer. Our results show that fenvalerate interacts more with the single stranded beta6.3 helical monomer or dimer than with the double helical form of gramicidin. This was further confirmed by an increase in the rate of gramicidin mediated proton transport in liposomes by fenvalerate, using the pH sensitive fluorophore, pyranine.

Anti-Bacterial Agents↗
PubMed1998

Projection of HIV infection in Calcutta.

Starting with the base year of 1991, the HIV infection projection for 1992-99 for the total, as well as various high-risk sub-populations of Calcutta, the first of its kind is provided. These projections are based on statistical methodology developed in this paper. Our methodology for spread of HIV infection takes into account various social interactions and practices and also uses available data. Rates of these interactions and practices and estimates of demographic parameters used in making projections were obtained primarily from surveys and census data. Since one of these estimated rates, that of HIV transmission rate through heterosexual encounters between an infected and an uninfected had a large range, we have provided two sets of projections based on the largest of these rates (worst-case scenario) and another that is consistent with the available data. The total projection of the number of HIV infected cases in Calcutta for 1999 is between 49,000 and 1,26,000. Separate projections are also provided for high-risk sub-groups. Among these, the sex workers expectedly will continue to manifest the highest numbers of newly infected cases. The temporal rate of increase in prevalence is projected to be alarmingly higher in the general population than even among sex workers, although the actual prevalence will continue to be the lowest in the general population compared to all other sub-groups of the population.

Female↗
PubMed1997

Selective cytotoxicity of dermaseptin S3 toward intraerythrocytic Plasmodium falciparum and the underlying molecular basis.

The antimicrobial activity of various naturally occurring microbicidal peptides was reported to result from their interaction with microbial membrane. In this study, we investigated the cytotoxicity of the hemolytic peptide dermaseptin S4 (DS4) and the nonhemolytic peptide dermaseptin S3 (DS3) toward human erythrocytes infected by the malaria parasite Plasmodium falciparum. Both DS4 and DS3 inhibited the parasite's ability to incorporate [3H]hypoxanthine. However, while DS4 was toxic toward both the parasite and the host erythrocyte, DS3 was toxic only toward the intraerythrocytic parasite. To gain insight into the mechanism of this selective cytotoxicity, we labeled the peptides with fluorescent probes and investigated their organization in solution and in membranes. In Plasmodium-infected cells, rhodamine-labeled peptides interacted directly with the intracellular parasite, in contrast to noninfected cells, where the peptides remained bound to the erythrocyte plasma membrane. Binding experiments to phospholipid membranes revealed that DS3 and DS4 had similar binding characteristics. Membrane permeation studies indicated that the peptides were equally potent in permeating phosphatidylserine/phosphatidylcholine vesicles, whereas DS4 was more permeative with phosphatidylcholine vesicles. In aqueous solutions, DS4 was found to be in a higher aggregation state. Nevertheless, both DS3 and DS4 spontaneously dissociated to monomers upon interaction with vesicles, albeit with different kinetics. In light of these results, we propose a mechanism by which dermaseptins permeate cells and affect intraerythrocytic parasites.

Amino Acid Sequence↗
PubMed1997

A leucine zipper motif in the ectodomain of Sendai virus fusion protein assembles in solution and in membranes and specifically binds biologically-active peptides and the virus.

We have detected a leucine zipper-like motif in the ectodomain of the Sendai virus fusion protein (aa 269-307) which is extremely conserved in the family of Sendai viruses. To find a possible role for this motif, we synthesized SV-269, a 39 amino acid peptide corresponding to this domain, and a mutant peptide, MuSV-269, with an amino acid pair interchanged their positions. The peptides were labeled with fluorescent probes at their N-terminal amino acid and functionally and structurally characterized. The data show that SV-269, but not MuSV-269, specifically binds Sendai virus. Expectedly, SV-269 is more active than the mutant MuSV-269 in inhibiting Sendai virus-mediated hemolysis. Fluorescence studies reveal that SV-269 assembles in aqueous solution, binds to zwitterionic PC and negatively-charged PS/PC vesicles, and assembles therein. Although MuSV-269 similarly binds to both types of vesicles, it only slightly assembles in solution and not at all in membranes. Moreover, SV-269, but not MuSV-269, coassembles with the biologically-active heptad repeats SV-150 and SV-473 (Rapaport et al. , 1995) in solution as revealed by fluorescence and circular dichroism (CD) spectroscopy, and with SV-150 within negatively-charged PS/PC and zwitterionic PC vesicles. Despite these differences, both SV-269 and MuSV-269 adopt similar secondary structures in 40% TFE and 1% SDS as revealed by CD spectroscopy, and disrupt the packing of the lipid bilayers to the same extent, as shown by the dissipation of diffusion potential. The role of this leucine zipper motif is discussed in terms of the assembly of the Sendai virus fusion protein in solution and within membranes. Since most of the heptadic leucines are also conserved in the corresponding domains of other paramyxoviruses such as rinderpest, measles, SV5, and parainfluenza, it may indicate a similar role of this domain in these viruses as well.

Amino Acid Sequence↗
PubMed1992

Spectroscopic probe of distribution of the non-intercalating drug netropsin between DNA and heparin.

Circular dichroism has been used as a monitoring tool to probe the distribution of the non-intercalating drug netropsin (NTPS) between the two biomolecules DNA and heparin. The stoichiometry of the interaction of the individual biomolecules and the drug is determined from conductometric titrations; the titration in each case shows two breaks corresponding to two stoichiometries of interaction. Though netropsin is non-intercalating, DNA wins over heparin in binding the drug due to strong hydrogen bonding capability of NTPS in the minor grooves of DNA through its greater than NH donor groups. Potential hydrogen bond breakers like KF and urea reduce the induced dichroism of NTPS-DNA system, probably dislodging some drug from DNA through hydrogen bond breaking.

Animals↗
PubMed1990

Studies on the conformation of and metal ion binding by teichoic acid of Staphylococcus aureus.

Teichoic acid (TA) isolated from the gram-positive bacteria S. aureus binds cationic dyes like pinacyanol (PCYN), 1,9-dimethyl methylene blue, acridine orange, etc., depicting blue-shifted metachromasia, and they bind the cationic dye carbocyanine depicting the red-shifted J band. TAs do not show any uv absorption band, and exhibition of tailing CD in the short uv region hints at its chiral conformation. Chiral conformation of TA has been confirmed from the induction of strong biphasic CD in the TA-carbocyanine system. Relative affinities for Ca2+, Mg2+, and Na+ have been probed from the disruption of metachromasia of the TA-dye system by these ions. Results show Ca2+ and Mg2+ to be almost equally effective in destroying the metachromasia of the TA-PCYN system, thus not supporting the hypothesis of special affinity for Mg2+ ion.

Calcium↗
PubMed1989

Spectrophotometric and spectrofluorometric titrations of teichoic acid.

Spectrophotometric and spectrofluorometric titrations of two strongly aggregating dyes, 1,9-dimethylmethylene blue (DMMB) and acridine orange (AO), by three anionic biopolymers, chondroitin sulphate A, DNA and teichoic acid (TA), have been described. Though the three polymers differ in their dye binding efficiencies and TA is a weak chromotrope, the equivalent weights of the polymers can be estimated accurately by these methods using the two dyes. Results show DMMB to be the preferred dye for spectrophotometric titration. The titrations can be used to estimate the equivalent weights of anionic polymers, and also for the quantitative estimation of such polymers of known equivalent weights.

Acridine Orange↗