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V Nagarajan

Publications and source records attributed to V Nagarajan.

13 recordsLinked to original sources
PubMed1992

Modular expression and secretion vectors for Bacillus subtilis.

A modular vector system has been developed for the extracellular production of heterologous proteins in Bacillus subtilis. This modular vector system consists of four secretion vectors which are based upon the genes encoding the Bacillus amyloliquefaciens extracellular alkaline protease, neutral protease, barnase and levansucrase. The modular vectors contain compatible restriction sites downstream from the signal peptide-coding region. Three reporter proteins (staphylococcal protein A, levansucrase and Escherichia coli alkaline phosphatase) that offer complementary advantages for cloning, genetic manipulations and media optimization have been fused to the various signal peptides. These secretion vectors function in E. coli and hence can be used to compare the mechanisms of protein secretion in E. coli and B. subtilis.

Alkaline Phosphatase↗
PubMed1992

Characterization of the secretion efficiency of a plant signal peptide in Bacillus subtilis.

The ability of the Bacillus subtilis secretion machinery to interact with a heterologous signal peptide was studied using a plant (wheat alpha-amylase) signal peptide. The plant signal peptide was capable of mediating secretion of Escherichia coli alkaline phosphatase and B. amyloliquefaciens levansucrase from B. subtilis. This secretion was dependent on the plant signal peptide, as deletion of five amino acids from the hydrophobic core resulted in a block of secretion. Attempts to improve the efficiency of the plant signal peptide in B. subtilis were made by increasing the length of the hydrophobic core from 10 to 16 residues by insertion of 2, 4, 5 or 6 amino acids. None of the alterations improved the secretion efficiency relative to the wild-type plant signal peptide.

Alkaline Phosphatase↗
PubMed1991

Effect of signal sequence alterations on export of levansucrase in Bacillus subtilis.

A series of alterations in the Bacillus amyloliquefaciens levansucrase signal peptide were made by in vitro mutagenesis, and their effect on the secretion of levansucrase in Bacillus subtilis was studied. Some of the alterations resulted in a completely defective signal peptide. These included the removal of positively charged residues from the N-terminus and disruption of the hydrophobic core of the signal peptide either by introducing a charged residue or by deleting five or more amino acids. Analysis of the signal peptide processing-site alterations revealed that small residues are preferred at the -1 and -3 positions. However, a wide variety of amino acids are tolerated at the +1 position.

Amino Acid Sequence↗
PubMed1990

Effect of specific mutations of tyrosine-(M)210 on the primary photosynthetic electron-transfer process in Rhodobacter sphaeroides.

We have measured the rate of the initial electron-transfer process as a function of temperature in reaction centers in a native strain of the photosynthetic bacterium Rhodobacter sphaeroides and two mutants generated by site-directed mutagenesis. In the mutants, a tyrosine residue in the vicinity of the primary electron donor and acceptor molecules was replaced by either phenylalanine or isoleucine. The electron-transfer reaction is slower in the mutants and has a qualitatively different dependence on temperature. In native reaction centers the rate increases as the temperature is reduced, in the phenylalanine mutant it is virtually independent of temperature, and in the isoleucine mutant it decreases with decreasing temperature. At 77 K, the electron-transfer reaction is approximately 30 times slower in the isoleucine mutant than in the native. These observations support the view that tyrosine-(M)210 plays an important role in the electron-transfer mechanism. In the isoleucine mutant at low temperatures, the stimulated emission from the excited reaction center undergoes a time-dependent shift to shorter wavelengths.

Electron Transport↗
PubMed1977

The problem of aflatoxic human disease in parts of India-epidemiological and ecological aspects.

An outbreak of a disease characterised by jaundice, rapidly developing ascites and portal hypertension associated with 20 p. 100 mortality rate was investigated in 1974. Analysis of food samples revealed that the disease outbreak was due to the consumption of maize (corn) heavily infested with the fungus Aspergillus flavus. Unseasonal rains prior to harvest, chronic drought conditions, poor storage facilities and ignorance of dangers of consuming fungal contaminated food seem to have caused the outbreak. The level of aflatoxin in food samples consumed during the outbreak was ranging between 2.5 and 15.6 microgram/g. Anywhere between 2 and 6 mg of aflatoxin seems to have been consumed daily by the affected people for many weeks. In contrast, during 1975, analysis of corn samples from the same areas revealed very low levels of aflatoxin, viz., less than 0.1 microgram/g. This was in line with the absence of major outbreak in 1975.

Adolescent↗
PubMed1976

Resistance of cold-exposed rats to aflatoxin.

Male rats kept at a temperature of 4 degrees-5 degrees C were refractory to a lethal dose of aflatoxin compared to animals at 20 degrees-21 degrees C which exhibited a high mortality and marked liver damage. It is suggested that this decreased susceptibility is mediated through a stimulated microsomal drug-metabolizing system in cold environment.

Aflatoxins↗
PubMed1975

Microsomal metabolism as a determinant of aflatoxin toxicity.

The evidences to incriminate the possible role of microsomal drug metabolizing system in aflatoxin toxicity in rat have been reviewed. It is suggested that an effective drug metabolism results in decreased acute toxicity and the products of metabolism are more carcinogenic than the native toxin to the rat liver.

Aflatoxins↗
PubMed1975

Hepatitis due to aflatoxicosis. An outbreak in Western India.

Parts of Western India have experienced an outbreak of hepatitis affecting man and dogs and characterised by jaundice, rapidly developing ascites, portal hypertension, and a high mortality-rate. The disease was associated with the consumption of maize contaminated heavily with Aspergillus flavus. Analysis of contaminated samples showed that affected people could have consumed between 2 and 6 mg. of aflatoxin daily over a period of a month. A specimen of liver obtained at necropsy showed bileduct proliferation and giant cells. The disease appears to be a result of aflatoxicosis.

Adult↗
PubMedDate not supplied

Levansucrase: a tool to study protein secretion in Bacillus subtilis.

The Bacillus amyloliquefaciens levansucrase gene (sacB[BamP]) was engineered in such a way that a heterologous gene could be inserted between the second and third codon of the mature levansucrase. Extracellular levansucrase activity was detected only when the heterologous protein was secreted into the growth medium. A positive selection system to isolate suppressors of signal sequence mutants in Bacillus subtilis has been developed based on the secretion of levansucrase.

Bacillus subtilis↗