The primary structure and function of nucleoside diphosphate kinase (NDK), a substrate non-specific enzyme involved in the maintenance of nucleotide pools is also implicated to play pivotal roles in many other cellular processes. NDK is conserved from bacteria to human and forms a homotetramer or hexamer to exhibit its biological activity. However, the nature of the functional oligomeric form of the enzyme differs among different organisms. The functional form of NDKs from many bacterial systems, including that of the human pathogen, Mycobacterium tuberculosis (MtuNDK), is a hexamer, although some bacterial NDKs are tetrameric in nature. The present study addresses the oligomeric property of MsmNDK and how a dimer, the basic subunit of a functional hexamer, is stabilized by hydrogen bonds and hydrophobic interactions. Homology modeling was generated using the three-dimensional structure of MtuNDK as a template; the residues interacting at the monomermonomer interface of MsmNDK were mapped. Using recombinant enzymes of wild type, catalytically inactive mutant, and monomer-monomer interactive mutants of MsmNDK, the stability of the dimer was verified under heat, SDS, low pH, and methanol. The predicted residues (Gln17, Ser24 and Glu27) were engaged in dimer formation, however the mutated proteins retained the ATPase and GTPase activity even after introducing single (Ms-mNDK-Q17A, MsmNDK-E27A, and MsmNDK-E27Q) and double (MsmNDK-E27A/Q17A) mutation. However, the monomer-monomer interaction could be abolished using methanol, indicating the stabilization of the monomer-monomer interaction by hydrophobic interaction.
Abstract-Nucleoside diphosphate kinase, NDK, plays a vital role in maintaining pools of nucleoside triphosphates and their respective deoxynucleoside triphosphates for the synthesis of RNA and DNA. Transcriptional regulation of ndk in mycoacteria remains unknown, although modulation of ndk expression under stress conditions involving DNA and, RNA synthesis arrest and cell division arrest had been studied in several bacterial systems. Therefore, in the present study, the start sites of transcription of ndk of Mycobacterium smegmatis (Msmndk) were identified and putative promoter regions were predicted. Using transcriptional fusions of the cloned putative promoter regions to mycobacterial codon-optimised reporter gene, gfpm 2+ , promoter activity was examined under active phase of growth, nutrient starvation and other stress conditions involving DNA replication inhibition and cell division arrest. Msmndk was found to be expressed through two transcripts, T1 and T2, arising from P1 and P2 promoters, respectively. Both the promoters belonged to C group of mycobacterial promoters, which do not possess consensus to any known canonical sigma factor recognition sequences. The levels of T2, but not of T1, were found to be low under the different stress conditions studied. The data documents modulation of ndk transcripts in mycobacteria.
The results of the three years INP sequence study revealed the possibility of raising three crops in the sequance of groundnut - blackgram- gingelly or cumbu soybean or blackgram - gingelly under rainfed conditions, when the monsoon is early and well distributed. When monsoon is erratic raising of two crops in the sequences of groundnut + redgram or groundunt - mustard, or cumbu-soybean or cumbu-mustard were found to be ideal. Raising of second crop of rainfed groundnut after the harvest of July sown kharif groundnut was not economical. Simultaneous sowing of redgram as an intercrop in groundnut in 6:1 proportion gave better yield and net return (Rs.5163/ha) during normal as well as erratic monsoon years.
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