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T Ghosh

Publications and source records attributed to T Ghosh.

18 recordsLinked to original sources
PubMed2001

Molecular dynamics simulations of pressure effects on hydrophobic interactions.

We report results on the pressure effects on hydrophobic interactions obtained from molecular dynamics simulations of aqueous solutions of methanes in water. A wide range of pressures that is relevant to pressure denaturation of proteins is investigated. The characteristic features of water-mediated interactions between hydrophobic solutes are found to be pressure-dependent. In particular, with increasing pressure we find that (1) the solvent-separated configurations in the solute-solute potential of mean force (PMF) are stabilized with respect to the contact configurations; (2) the desolvation barrier increases monotonically with respect to both contact and solvent-separated configurations; (3) the locations of the minima and the barrier move toward shorter separations; and (4) pressure effects are considerably amplified for larger hydrophobic solutes. Together, these observations lend strong support to the picture of the pressure denaturation process proposed previously by Hummer et al. (Proc. Natl. Acad. Sci. U.S.A. 1998, 95, 1552): with increasing pressure, the transfer of water into protein interior becomes key to the pressure denaturation process, leading to the dissociation of close hydrophobic contacts and subsequent swelling of the hydrophobic protein interior through insertions of water molecules. The pressure dependence of the PMF between larger hydrophobic solutes shows that pressure effects on the interaction between hydrophobic amino acids may be considerably amplified compared to those on the methane-methane PMF.

Computer Simulation↗
PubMed2001

Molecular characterization of the VP7 gene of Rotavirus isolated from a clinical sample of Calcutta, India.

The gene coding for outer capsid protein, VP7 of rotaviruses detected among the children suffering from watery diarrhea in the eastern part of India was studied. The full length gene, coding for VP7 was synthesized from a local strain, WD33, by combined reverse transcriptase-polymerase chain reaction. A total of 42 fecal RNA out of 93 rotavirus-positive samples hybridized with this DNA, indicating the prevalence of this strain in the community. Comparison of the nucleotide and deduced amino acid sequence with the VP7 gene of other serotypes revealed that the local strain,WD33, resembled closely with G1 serotype, the homology being 94 and 97%, respectively. Multiplex PCR using the specific oligonucleotide primers also amplified the G1 specific DNA fragment. The overall change of 16 amino acids was noticed when compared with G1 specific prototype Wa strain of which nine amino acids are within the neutralization domain. However, the phylogenetic tree constructed by comparing the G1 strains from different countries demonstrated that this strain WD33 clustered as a distinct sub-lineage of lineage IV and not with Wa strain, that clustered with lineage III.

Amino Acid Sequence↗
PubMed1998

The D arm of tRNATyr is necessary and sufficient for import into Leishmania mitochondria in vitro.

Transfer RNAs are selectively imported from the cytoplasm into mitochondria of kinetoplastid protozoa such as Leishmania . The specific structural features of tRNA which determine selectivity are largely unknown. Using an in organello system from Leishmania , the import signals on tRNATyrand on a synthetic transcript which binds to the same receptor, were studied by deletion and reconstruction analyses. In both cases, short oligoribonucleotides (minihelices) containing the sequence UGGYAGAG were imported with high efficiency in the presence of ATP. This motif is present in the D arm of tRNATyr, as well as in the majority of imported Leishmania tRNAs. Deletion of the D arm, or a point mutation in the conserved motif, reduces importability. The import signal coincides with the binding site for the mitochondrial receptor TAB. tRNAGln, which is not imported, forms non-productive, TAB-independent complexes with the mitochondrial surface. However, the observation that the imported:bound ratio of the D arm minihelix is higher than that of the entire molecule suggests that the post-binding translocation step is constrained in terms of size or structural flexibility. Kinetic studies of minihelix import indicate stepwise insertion of the molecule into import channels.

Animals↗
PubMed1997

Role of an RNA-binding protein in import of tRNA into Leishmania mitochondria.

Nuclear-encoded cytoplasmic tRNAs are imported into the mitochondria of kinetoplastid protozoa by an unknown mechanism. In a Leishmania in organello system, ATP-dependent import of a cloned, unspliced tRNATyr(GUA) transcript was demonstrated by protection from ribonuclease, whereas import of a tRNAGln(CUG) transcript was much less efficient. Specific binding of tRNATyr to two mitochondrial surface proteins of 15 and 22 kilodaltons was observed. Tubulin antisense-binding protein (TAB), the 15-kilodaton species, was purified to apparent homogeneity by RNA affinity chromatography. TAB forms stable complexes with the D stem-loop region of tRNATyr. Immunocytochemical and cell fractionation experiments, combined with limited proteolysis, suggested the association of TAB with the outer mitochondrial membrane. Importantly, anti-TAB antibody specifically inhibited binding as well as import of tRNATyr and of a synthetic structural homolog. These results support the role of TAB as a membrane-bound receptor or carrier for RNA import into Leishmania mitochondria.

Animals↗
PubMed1995

Metal ion interaction with penicillins--Part VII: Mixed-ligand complex formation of cobalt(II), nickel(II), copper(II), and Zinc(II) with ampicillin and nucleic bases.

Equilibrium study on the mixed-ligand complex formation of M2+ ions (M = Co, Ni, Cu, and Zn) with alpha-d-(-)aminobenzyl penicillin popularly known as ampicillin, (hereafter, ampH +/-), and nucleic bases, viz. adenine, guanine, thymine, uracil, and cytosine (B), in aqueous solution at 37 degrees C at a fixed ionic strength, I = 0.1 M (NaNO3) indicates the formation of complexes of the types: M(amp), M(B), M(amp)(B), M(H-1 amp)(B), and M(H-1 amp)(B)(OH). Stability constants of the ternary complexes are in the order: Co2+ < Ni2+ < Cu2+ > Zn2+ with regard to the mental ions and guanine > adenine > uracil > thymine > cytosine with regard to the nucleic bases. Complex formation equilibria have been worked out on the basis of species distribution curves.

Ampicillin↗
PubMed1994

Import of small RNAs into Leishmania mitochondria in vitro.

Using an in vitro ribonuclease protection assay, it was shown that synthetic antisense transcripts from the 5'-upstream region of the beta-tubulin gene are efficiently imported into isolated Leishmania mitochondria. Import occurred after a lag of about 30 min at 25 degrees C and was dependent on ATP. Preincubation experiments suggested that import consists of a slow interaction of mitochondria with RNA, followed by rapid ATP-dependent uptake. Import was saturable with antisense RNA at about 1 nM concentration, and sequence-specific, as shown by lack of import of other labelled transcripts. Deletion analysis demonstrated a correlation between efficiency of import and the number of oligopurine motifs on the antisense RNA. Several small ribosomal RNAs (srRNAs) and Leishmania tRNA competed with antisense RNA for import. Incubation of mitochondria with srRNAs and tRNA in the presence of radiolabelled UTP resulted in the ribonuclease-resistant labelling of these RNAs by the mitochondrial terminal uridylyl transferase. Extracts of isolated mitochondria contain a factor binding to antisense RNA, as shown by gel retardation assay. These observations indicate the presence of a receptor-mediated import pathway for srRNAs and tRNA in Leishmania mitochondria.

Adenosine Triphosphate↗
PubMed1994

Interaction of small ribosomal and transfer RNAs with a protein from Leishmania donovani.

Using synthetic antisense RNA from the 5'-untranslated region of the beta-tubulin gene as probe in gel retardation assays, a heat stable RNA-binding factor was identified in promastigotes of the kinetoplastid protozoan Leishmania donovani. The same or similar factors interact with several small ribosomal RNA (srRNA) species and, more weakly, with tRNA, as shown by binding and competition experiments. Deletion analysis indicated involvement of repeated purine-rich motifs on the antisense RNA, in the reaction. Related, conserved motifs occur on at least two of the srRNAs. By a modified Western blot assay, the RNA-binding species was identified as a single, small polypeptide. The activity is apparently specific for the promastigote stage of the parasite, being undetectable in amastigotes. The properties of this RNA-binding factor suggest that it is a novel, previously uncharacterized protein.

Animals↗
PubMed1980

Cyproterone acetate and seminal vesicles in the regulation of male fertility.

The effect of continuous release of microquantities of cyproterone acetate from subcutaneously implanted silastic capsules on the fertility of surgically manipulated seminal vesicles of rat has been studied. The experimental animals showed infertility for 3 weeks, as a consequence of removal of seminal plasma, following which normal fertility returns as efficiently as that operated control. However, a significant decrease in weight of the testes and epididymides, were recorded. It appears that seminal vesicles can synthesize seminal plasma even at very low levels of androgen in the presence of cyproterone acetate.

Animals↗
PubMed1977

Surgical and postoperative problems with Binkhorst 2- and 4-loop lenses.

The operative and postoperative complications are described in a series of 537 eyes with lens implants, with suggestions for prophylaxis and treatment. The level of complications is low, and the authors believe that the visual results in terms of patient satisfaction make lens implantation a worthwhile procedure.

Adolescent↗
PubMedDate not supplied

Blood group genotypes in Zambia and linkage to sickle cell disease.

A number of normal Zambian individuals, Sickle cell heterozygotes and homozygotes, of different tribes living in Livingstone, were studied for Rh and MNSs genotypes. The purpose of this study was to establish the frequency distribution of these antigens in the normal Zambian. An attempt was also made to find the degree of linkage between Rh, MNSs with Sickle cell genes. cDe genes were found to bear a linear relationship amongst normal Zambians, heterozygotes and homozygotes, thus making the cDe antigen very prevalent in Zambia. MN antigens are however unevenly distributed. There is also a positive straight line relationship in the absence of S and s antigens amongst normal individuals, heterogygotes and homozygotes. Su, an allele of Ss system commonly found in Africa is also prevalent in Zambia. The linkage between cDe, MN, Ss genes and Sickle cell genes seems to be insignificant (P = 0.1 or greater than 0.1). The finding of a high percentage of cDe genes in normal Zambian individuals should help the clinicians in solving medico-legal disputes in the study of various genetic and anthropological problems.

Anemia, Sickle Cell↗