Biomedical subjects

S Mahapatra

Publications and source records attributed to S Mahapatra.

At least 37 records · Page 2Linked to original sources

PubMed2001

Biosynthesis of the arabinogalactan-peptidoglycan complex of Mycobacterium tuberculosis.

The compositional complexity of the mycobacterial cell envelope differentiates Mycobacterium species from most other prokaryotes. Historically, research in this area has focused on the elucidation of the structure of the mycobacterial cell envelope with the result that the structures of the mycolic acid-arabinogalactan-peptidoglycan complex from M. tuberculosis are fairly well understood. However, the current impetus for studying M. tuberculosis and other pathogenic mycobacteria is the need to identify targets for the development of new drugs. Therefore, emphasis has been shifting to the study of cell envelope biosynthesis and the identification of enzymes that are essential to the viability of M. tuberculosis. The publication of the complete M. tuberculosis genome in 1998 has greatly aided these studies. To date, thirteen enzymes involved in the synthesis of the arabinogalactan-peptidoglycan complex of M. tuberculosis have been identified and at least partially characterized. Eleven of these enzymes were reported subsequent to the publication of the M. tuberculosis genome, a clear indication of the rapid evolution of knowledge stimulated by the sequencing of the genome. In this article we review the current understanding of M. tuberculosis arabinogalactan-peptidoglycan structure and biosynthesis.

Carbohydrate Conformation↗

PubMed2001

Further biochemical characterization of Mycobacterium leprae laminin-binding proteins.

It has been demonstrated that the alpha2 chain of laminin-2 present on the surface of Schwann cells is involved in the process of attachment of Mycobacterium leprae to these cells. Searching for M. leprae laminin-binding molecules, in a previous study we isolated and characterized the cationic proteins histone-like protein (Hlp) and ribosomal proteins S4 and S5 as potential adhesins involved in M. leprae-Schwann cell interaction. Hlp was shown to bind alpha2-laminins and to greatly enhance the attachment of mycobacteria to ST88-14 Schwann cells. In the present study, we investigated the laminin-binding capacity of the ribosomal proteins S4 and S5. The genes coding for these proteins were PCR amplified and their recombinant products were shown to bind alpha2-laminins in overlay assays. However, when tested in ELISA-based assays and in adhesion assays with ST88-14 cells, in contrast to Hlp, S4 and S5 failed to bind laminin and act as adhesins. The laminin-binding property and adhesin capacity of two basic host-derived proteins were also tested, and only histones, but not cytochrome c, were able to increase bacterial attachment to ST88-14 cells. Our data suggest that the alanine/lysine-rich sequences shared by Hlp and eukaryotic H1 histones might be involved in the binding of these cationic proteins to laminin.

Animals↗

PubMed2000

Characterization of derivatives of the high-molecular-mass penicillin-binding protein (PBP) 1 of Mycobacterium leprae.

Mycobacterium leprae has two high-molecular-mass multimodular penicillin-binding proteins (PBPs) of class A, termed PBP1 and PBP1* [Lepage, Dubois, Ghosh, Joris, Mahapatra, Kundu, Basu, Chakrabarti, Cole, Nguyen-Disteche and Ghuysen (1997) J. Bacteriol. 179, 4627-4630]. PBP1-Xaa-beta-lactamase fusions generated periplasmic beta-lactamase activity when Xaa (the amino acid of PBP1 at the fusion junction) was residue 314, 363, 407, 450 or 480. Truncation of the N-terminal part of the protein up to residue Leu-147 generated a penicillin-binding polypeptide which could still associate with the plasma membrane, whereas [DeltaM1-R314]PBP1 (PBP1 lacking residues Met-1 to Arg-314) failed to associate with the membrane, suggesting that the region between residues Leu-147 and Arg-314 harbours an additional plasma membrane association site for PBP1. Truncation of the C-terminus up to 42 residues downstream of the KTG (Lys-Thr-Gly) motif also generated a polypeptide that retained penicillin-binding activity. [DeltaM1-R314]PBP1 could be extracted from inclusion bodies and refolded under appropriate conditions to give a form capable of binding penicillin with the same efficiency as full-length PBP1. This is, to the best of our knowledge, the first report of a soluble derivative of a penicillin-resistant high-molecular-mass PBP of class A that is capable of binding penicillin. A chimaeric PBP in which the penicillin-binding (PB) module of PBP1 was fused at its N-terminal end with the non-penicillin-binding (n-PB) module of PBP1* retained pencillin-binding activity similar to that of PBP1, corroborating the finding that the n-PB module of PBP1 is dispensable for its penicillin-binding activity.

Bacterial Proteins↗

PubMed2000

Solubilization Site of Organic Perfume Molecules in Sodium Dodecyl Sulfate Micelles: New Insights from Proton NMR Studies.

The site of incorporation of solubilizates in sodium dodecyl sulfate (SDS) micellar systems has been investigated by proton NMR spectroscopy. The solubilizate molecules chosen for the present study are phenol, 4-methylphenol, 4-allyl-2-methoxyphenol, anisole, 4-methylanisole, 4-propenylanisole, 1,8-cineole, and limonene. These molecules possess a wide variety of functional groups with different degrees of hydrophilic/hydrophobic character and are thereby solubilized at different micellar locations. Aromatic compounds, especially those having a phenolic-OH group, showed a large upfield shift of SDS methylene protons that are closely linked to the terminal sulfate groups. Additionally, in the case of phenolic compounds, the unresolved signals of the nine straight-chain bulk methylene protons of SDS are split into a broad doublet with uneven intensity. This splitting of methylene protons was found to be dependent on the concentration of the substrate. Based on these observations, probable solubilization sites and orientation of the substrate molecule within the micelles are discussed. Phenolic compounds, being the most hydrophilic among the present set, reside at the hydrophilic/hydrophobic boundary of micelle-water interface and thus influence the resonances of SDS protons the most. Aromatic methoxy and aliphatic compounds, being relatively more hydrophobic in nature, reside inside the micellar core and thereby result in smaller shifts. Copyright 2000 Academic Press.

Journal Article↗

PubMed2000

Daily intake of manganese by the adult population of Mumbai.

The daily intake of manganese (Mn) estimated through air, water and duplicate dietary analysis is found to range from 0.67 to 4.99 mg with a mean value of 2.21 mg. Ingestion through food contributed to the predominant fraction of the intake. The turnover rate of Mn through blood is approximately 2 h, based on the mean concentration of Mn in blood of 1.54 microg l(-1). The average concentrations of Mn in water and air were approximately 1.42 microg l(-1) and 37 ng m(-3), respectively. The daily intake of Mn by the adult population of Mumbai is closer to the lower bound of the recommended limit of 2-5 mg. Electro Thermal Atomic Absorption Spectrophotometry (ET-AAS), has been used for the determination of Mn in a variety of environmental and human biological fluids. The detection limit of Mn for a volume injection of 20 microl is 2 pg absolute. The precision of the method is established by analyzing a synthetic mixture containing various elements in different quantities (0.5-10 ppm) and is found to be within +/- 8%. The reliability of estimation is further assessed through the analysis of Standard Reference Materials (SRMs) of soil, hay, milk powder and fish tissue obtained from IAEA.

Adult↗

PubMed2000

Analysis of intracardiac electrograms showing monomorphic ventricular tachycardia in patients with implantable cardioverter-defibrillators.

Ventricular tachycardia (VT) initiation and its relation to various clinical factors was studied by reviewing intracardiac electrograms from patients with implantable cardioverter-defibrillators. Events were divided into (1) sudden onset without preceding ventricular premature complexes (VPCs), (2) extrasystolic onset with VPCs, or (3) paced, depending on the type and morphology of the last 5 beats before initiation of VT. Prematurity index, sinus rate, cycle length, and presence of short-long-short sequence for each episode was noted. A total of 268 episodes of VT among 52 patients were analyzed. Extrasystolic initiation was the most frequent pattern (177; 66%) followed by sudden onset (75; 28%) and paced (16; 6%). Among extrasystolic onset, 99 episodes (56%) were due to multiple VPCs and 149 episodes (84%) had different VPC morphology than the subsequent VT. Among pacing-induced VT, 13 of 16 episodes were due to inappropriate pacing due to undersensing of prior R waves. Sudden-onset episodes were slower (mean cycle length 383+/-97 ms) than extrasystolic (mean cycle length 336+/-88 ms, p = 0.002) and paced (mean cycle length 313+/-85 ms, p = 0.01) onset. Patients in the sudden-onset group had better left ventricular ejection fraction (33+/-15%) than the extrasystolic (29+/-11%, p<0.001) and paced (28+/-14%, p<0.01) groups. Extrasystolic onset with multiple, late coupled VPCs was the most common pattern of VT initiation and was associated with lower ejection fraction. Sudden-onset initiation was more common with better preserved systolic function.

Aged↗

PubMed2000

Bacterial and host-derived cationic proteins bind alpha2-laminins and enhance Mycobacterium leprae attachment to human Schwann cells.

It has recently been demonstrated that laminin alpha2 chains present on the surface of Schwann cells are involved in the process of attachment of Mycobacterium leprae to these cells. In this study, a protein in the M. leprae cell wall that was found to be capable of binding alpha2-containing laminins (merosin) was isolated and characterized. The M. leprae laminin-binding protein was identified as a 21-kDa histone-like protein (Hlp), a highly conserved cationic protein present in other species of mycobacteria. The gene that encodes this protein was PCR amplified, cloned, and expressed, and the recombinant protein was shown to bind alpha2-laminins. More significantly, when added exogenously, Hlp was able to greatly enhance the attachment of mycobacteria to ST88-14 human Schwann cells. The capacity to bind alpha2-laminins and to enhance mycobacterial adherence to Schwann cells was also found in other cationic proteins such as host-derived histones. Moreover, mutation in the hlp gene was shown not to affect the capacity of mycobacteria to bind to ST88-14 cells, suggesting that alternative adhesins and/or pathways might be used by mycobacteria during the process of adherence to Schwann cells. The potential role of Hlp as a fortuitous virulence factor contributing to the pathogenesis of M. leprae-mediated nerve damage is discussed.

Adhesins, Bacterial↗

PubMed2000

Comparison of the UDP-N-acetylmuramate:L-alanine ligase enzymes from Mycobacterium tuberculosis and Mycobacterium leprae.

In the peptidoglycan of Mycobacterium leprae, L-alanine of the side chain is replaced by glycine. When expressed in Escherichia coli, MurC (UDP-N-acetyl-muramate:L-alanine ligase) of M. leprae showed K(m) and V(max) for L-alanine and glycine similar to those of Mycobacterium tuberculosis MurC, suggesting that another explanation should be sought for the presence of glycine.

Alanine↗

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↗

PubMed1998

Study on body mass index, lipid profile and lipid peroxidation status in coronary artery disease.

Among the many known risk factors of coronary artery disease (CAD) obesity and hypercholesterolaemia are important ones. Whatever may be the risk factor, the basic pathology of CAD is deposition of altered lipids on the endothelium. One of such altered lipid is oxidatively modified low density lipoprotein (LDL). Lipid peroxidation has been assessed by several methods. Quantitation of malondialdehyde (MDA) by thiobarbituric acid (TBA) method is one of the commonly utilised method in several laboratories. In this study 40 cases of CAD were selected for evaluation. The body mass index (BMI), lipid profile and the level of lipid peroxidation (MDA) were measured. Seventeen cases (42.5%) had normal BMI (20-25), 20 cases (50%) were in the overweight range of BMI (26-30) and only 3 cases (7.5%) were in the obese group with a BMI more than 30. BMI correlated better with the level of total cholesterol (Tc), low density lipoprotein cholesterol (HDLc) and MDA. BMI did not show any correlation with triglyceride (Tg) or high density lipoprotein cholesterol (HDLc). MDA level correlated better with Tc, Tg levels and BMI, poorly correlated with LDLc and in inverse relationship was observed with HDLc.

Aged↗

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↗

PubMed1997

Dual multimodular class A penicillin-binding proteins in Mycobacterium leprae.

The ponA gene of cosmid L222 of the Mycobacterium leprae genome library encodes a multimodular class A penicillin-binding protein (PBP), PBP1. The PBP, labelled with a polyhistidine sequence, has been produced in Escherichia coli, extracted from the membranes with 3-[(3-cholamidopropyl)-dimethylammonio]-1-propane-sulfonate (CHAPS) and purified by Ni2(+)-nitrilotriacetic acid-agarose chromatography. In contrast to the pon1-encoded class A PBP1, PBP1 undergoes denaturation at temperatures higher than 25 degrees C, it catalyzes acyl transfer reactions on properly structured thiolesters, and it binds penicillin with high affinity.

Acylation↗

PubMed1996

Biochemical characterization of the 49 kDa penicillin-binding protein of Mycobacterium smegmatis.

The 49 kDa penicillin-binding protein (PBP) of Mycobacterium smegmatis catalyses the hydrolysis of the peptide or S-ester bond of carbonyl donors R1-CONH-CHR2-COX-CHR2-COO- (where X is NH or S). In the presence of a suitable amino acceptor, the reaction partitions between the transpeptidation and hydrolysis pathways, with the amino acceptor, behaving as a simple alternative nucleophile at the level of the acyl-enzyme. By virtue of its N-terminal sequence similarity, the 49 kDa PBP represents one of the class of monofunctional low-molecular-mass PBPs. An immunologically related protein of M(r) 52,000 is present in M. tuberculosis. The 49 kDa PBP is sensitive towards amoxycillin, imipenem, flomoxef and cefoxitin.

Amino Acid Sequence↗

PubMed1996

Import of RNA into Leishmania mitochondria occurs through direct interaction with membrane-bound receptors.

Cytoplasmic tRNAs are imported into the kinetoplast mitochondrion of Leishmania, but the mechanism of import is unknown, particularly whether RNA is transferred as a ribonucleoprotein complex through the protein import pathway or by a distinct receptor-mediated mechanism. Using isolated mitochondria, it was shown that a small, importable RNA, which is structurally homologous to tRNA, binds rapidly, specifically, and with high affinity to the mitochondrial surface in the absence of soluble protein factors to form an import intermediate. Two classes of binding site of apparent Kd 0.3 and 10 n, respectively, were distinguished. tRNA from Leishmania, but not yeast, competitively inhibited the binding. Northwestern blot analysis revealed the presence of a 15-kDa RNA binding protein on the mitochondrial surface. Whereas receptor binding was resistant to heparin and KCl, internalization was sensitive to both reagents. These results are consistent with the presence of a direct mechanism of receptor-mediated RNA import on Leishmania mitochondria.

Adenosine Triphosphate↗

PubMed1996

Reversible cleavage and formation of the dioxygen O-O bond within a dicopper complex.

A key step in dioxygen evolution during photosynthesis is the oxidative generation of the O-O bond from water by a manganese cluster consisting of M2(mu-O)2 units (where M is manganese). The reverse reaction, reductive cleavage of the dioxygen O-O bond, is performed at a variety of dicopper and di-iron active sites in enzymes that catalyze important organic oxidations. Both processes can be envisioned to involve the interconversion of dimetal-dioxygen adducts, M2(O2), and isomers having M2(mu-O)2 cores. The viability of this notion has been demonstrated by the identification of an equilibrium between synthetic complexes having [Cu2(mu-eta2:eta2-O2)]2+ and [Cu2(mu-O)2]2+ cores through kinetic, spectroscopic, and crystallographic studies.

Chemical Phenomena↗

PubMed1996

Identification and overexpression in Escherichia coli of a Mycobacterium leprae gene, pon1, encoding a high-molecular-mass class A penicillin-binding protein, PBP1.

Cosmid B577, a member of the collection of ordered clones corresponding to the genome of Mycobacterium leprae, contains a gene, provisionally called pon1, that encodes an 821-amino-acid-residue high-molecular-mass class A penicillin-binding protein, provisionally called PBP1. With similar amino acid sequences and modular designs, M. leprae PBP1 is related to Escherichia coli PBP1a and PBP1b, bienzymatic proteins with transglycosylase and transpeptidase activities. When produced in E. coli, His tag-labelled derivatives of M. leprae PBP1 adopt the correct membrane topology, with the bulk of the polypeptide chain on the surface of the plasma membrane. They defy attempts at solubilization with all the detergents tested except cetyltrimethylammonium bromide. The solubilized PBP1 derivatives can be purified by affinity chromatography on Ni2+-nitrilotriacetic acid agarose. They have low affinities for the usual penicillins and cephalosporins.

Amino Acid Sequence↗

PubMed1995

Subclinical status epilepticus following ECT.

Subclinical status epilepticus is a rare complication of electroconvulsive therapy (ECT). We describe the case of a 70-year-old man with psychotic depression who developed prolonged subclinical status epilepticus following an initial ECT treatment; he subsequently received a course of ECT without complications. It is important to consider status epilepticus in the differential diagnosis of patients who do not regain consciousness following ECT, even in the absence of overt motor seizure activity. The development of this complication does not preclude the future use of ECT; in fact, ECT has been repeated successfully in individuals who developed this complication, including this case. Identification of potential risk factors, appropriate preventive measures, and early intervention are important in the management of this complication. The literature is reviewed and appropriate preventive and treatment measures are discussed.

Aged↗

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↗