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Biomedical subjects

P Ajitkumar

Publications and source records attributed to P Ajitkumar.

7 recordsLinked to original sources
PubMed1999

Growth inhibition of human promonocytic leukaemic U937 cells by interferon gamma is irreversible and not cell cycle phase-specific.

Growth of human promonocytic leukaemic U937 cells was found arrested within 24 h upon exposure to interferon gamma (IFN-gamma). Removal of the interferon did not result in the resumption of growth, as is evident from the absence of doubling of viable cell count and(3)H-thymidine incorporation. 5-Bromo-2'-deoxyuridine-based flow cytometric analysis of the growth-arrested cells, 24 h subsequent to the removal of IFN-gamma, showed absence of DNA synthesis, confirming the irreversible nature of the growth inhibition. Propidium iodide-based flow cytometric analysis of the growth-arrested cells showed a distribution which is typical of a growth inhibition without resulting in the accumulation of cells in any specific phase of the cell cycle. These results indicated that IFN-gamma arrested growth of U937 cells in an irreversible and cell cycle phase-independent manner. These observations were in contrast to our earlier report on the reversible and cell cycle phase-specific growth inhibition of human amniotic (fetal epithelial) WISH cells by the interferon.

Bromodeoxyuridine↗
PubMed1998

Cloning and expression of the gene coding for FtsH protease from Mycobacterium tuberculosis H37Rv.

This study was aimed at the molecular cloning and expression of the gene coding for FtsH protease of Mycobacterium tuberculosis H37Rv (virulent). PCR on the genomic DNA of M. tuberculosis H37Ra (non-virulent) using the oligodeoxynucleotide primers, which were designed based on the codon usage pattern of M. tuberculosis and against the nucleotide (nt) sequence corresponding to two conserved domains of the FtsH protein of Escherichia coli, yielded a 363-bp product. The amino-acid sequence, deduced from the nt sequence of the PCR product, revealed the presence of two ATP-binding motifs and the AAA Signature motif (Second Region of Homology) that are characteristic features found conserved in the FtsH molecules from eubacteria, archaebacteria, and eukaryotes. Southern hybridisation of the NheI digest of the cosmid SCY6F7 containing part of the genomic DNA of M. tuberculosis H37Rv using the PCR fragment as the probe identified the full-length ftsH gene in the 7.2-kb fragment. The gene was subcloned into pBS (SK+) vector, and the FtsH product that was expressed in E. coli transformed with the vector was identified as an 85-kDa protein localised in the membrane.

ATP-Dependent Proteases↗
PubMed1998

IFN-gamma inhibits growth of WISH cells in a cell cycle phase-specific manner.

Treatment of WISH (human amnion) cells with interferon-gamma (IFN-gamma) inhibits their growth. Release of the cells from IFN-gamma-mediated growth inhibition led to a rapid and significant increase in DNA synthesis, followed by doubling of cell numbers. The DNA synthesis profile was strikingly similar to that shown by WISH cells released from growth arrest by the G1/S phase inhibitor, aphidicolin. This strongly suggested that IFN-gamma treatment leads to growth inhibition of WISH cells at the G1/S boundary of the cell cycle. In contrast, IFN-alpha blocked growth of these cells at the G0/G1 boundary.

Amnion↗
PubMed1989

Use of mutants to analyze regions on the H-2Kb molecule for interaction with immune receptors.

MHC variants isolated both in vivo (by tissue graft rejection) and in vitro (by antibody selection) were utilized to study sites on the H-2Kb molecule involved in interaction with antibodies and with the TCR. Kb mutants selected by antibodies were found to have single point mutations, which when analyzed in the context of the three-dimensional structure of a Kb molecule modeled from HLA-A2 coordinates showed that the altered residues were localized mostly to the alpha 1 and alpha 2 helices. The side chains of the variant amino acid residues pointed upward and away from the antigenic site. Analysis of the altered amino acids in the previously described tissue-graft-selected Kb mutants showed that the side chains of the variant residues occur either in the alpha-helical regions or in the beta-pleated-sheet floor of the antigen groove, but every mutant contained at least one and sometimes several acid side chains projecting into the antigen-binding groove. Monoclonal antibody studies showed that the available monoclonal antibodies mapped to discrete domain-specific sites. Analysis of CTL recognition sites using cloned mutant anti-parent or allogeneic combinations showed that all CTL clones examined interacted with amino acid side-chain residues on both the alpha 1 and alpha 2 helices. Thus, we concluded that the CTLs must simultaneously interact with the amino acid residues in both the alpha-helical stretches of the alpha 1 and alpha 2 domains. Our analyses with the point mutants imply that the TCR must interact with the MHC molecule over a relatively large surface area in such an orientation that it interfaces with the two alpha helices, as well as with the foreign or self-peptide in the antigen-binding site between the helices. These findings, together with the observation that several of the in vivo Kb mutants induce strong alloreactions yet have changes only in the bottom of the antigen-binding groove and no alterations in the alpha-helical residues, are consistent with the hypothesis that in some cases alloreaction can be the result of T-cell recognition of an altered pattern on the MHC molecule due to a changed peptide in the antigen groove.

Amino Acid Sequence↗
PubMed1988

Evidence that multiple residues on both the alpha-helices of the class I MHC molecule are simultaneously recognized by the T cell receptor.

Single amino acid substitutions at nine different positions on the H-2Kb molecules from in vitro-mutagenized, immunologically altered, somatic cell variants were correlated with their patterns of recognition by monoclonal antibodies (MAbs) and allogeneic cytotoxic T lymphocyte (CTL) clones. While MAbs were found to detect spatially discrete, domain-specific sites, CTLs interacted simultaneously with multiple residues on the alpha 1 and alpha 2 domains of the Kb molecule. The computer graphic three-dimensional Kb model structure showed that, of the seven CTL-specific residues analyzed, six residues were located on the alpha-helical regions of the two domains. Every CTL clone was found to interact with a distinct pattern of residues composed of a specific subset of the CTL-specific residues.

Amino Acid Sequence↗
PubMed1985

Presence of 2-methylthioribosyl-trans-zeatin in Azotobacter vinelandii tRNA.

Hydroxylated cytokinin, 2-methylthio-N6-(4-hydroxy-3-methylbut-2-enyl) adenosine, was found in the tRNA of Azotobacter vinelandii. This cytokinin had the trans configuration, unlike the cis configuration reported for that from other bacteria. Culture-condition-dependent changes in the content of this thiocytokinin and a few other thionucleosides in the tRNA of this bacterium have been observed.

Azotobacter↗