• OM PRAKASH CHOUHAN

      Articles written in Journal of Biosciences

    • Effect of ions and inhibitors on the catalytic activity and structural stability of S. aureus enolase

      VIJAY HEMMADI AVIJIT DAS OM PRAKASH CHOUHAN SUMIT BISWAS MALABIKA BISWAS

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      The glycolytic enzyme enolase of Staphylococcus aureus is a highly conserved enzyme which binds to human plasminogenthereby aiding the infection process. The cloning, overexpression and purification of S. aureus enolase as well as the effectof various metals upon the catalytic activity and structural stability of the enzyme have been reported. The recombinantenzyme (rSaeno) has been purified to homogeneity in abundant amounts (60 mg/L of culture) and the kinetic parameters(Km = 0.23 ± 0.013 9 10-3 M; Vmax = 90.98 ± 0.00052 U/mg) and the optimum pH were calculated. This communicationfurther reports that increasing concentrations of Na? ions inhibit the enzyme while increasing concentrations of K?ions were stimulatory. In case of divalent cations, it was found that Mg2? stimulates the activity of rSaeno while the rest ofthe divalent cations (Zn2+, Mn2+, Fe2+, Cu2+, Ni2+ and Ca2+) lead to a dose-dependent loss in the activity with a total lossof activity in the presence of Hg2+ and Cr2+. The circular dichroism data indicate that other than Hg2+, Ni2+ and to acertain extent Cu2+, none of the other ions destabilized rSaeno. The inhibitory roles of fluorides, as well as neurotoxiccompounds upon the catalytic activity of rSaeno, have also been studied. Conformational changes in rSaeno (induced byions) were studied using partial trypsin digestion.

    • The conserved aspartate in motif III of b family AdoMet-dependent DNA methyltransferase is important for methylation

      AATHIRA GOPINATH MANASI KULKARNI ISHTIYAQ AHMED OM PRAKASH CHOUHAN KAYARAT SAIKRISHNAN

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      S-adenosyl-L-methionine (AdoMet)-dependent methyltransferases (MTases) are involved in diverse cellularfunctions. These enzymes show little sequence conservation but have a conserved structural fold. The DNAMTases have characteristic motifs that are involved in AdoMet binding, DNA target recognition and catalysis.Motif III of these MTases have a highly conserved acidic residue, often an aspartate, whose functionalsignificance is not clear. Here, we report a mutational study of the residue in the beta family MTase of the Type IIIrestriction-modification enzyme EcoP15I. Replacement of this residue by alanine affects its methylationactivity. We propose that this residue contributes to the affinity of the enzyme for AdoMet. Analysis of thestructures of DNA, RNA and protein MTases reveal that the acidic residue is conserved in all of them, andinteracts with N6 of the adenine moiety of AdoMet. Interestingly, in the SET-domain protein lysine MTases,which have a fold different from other AdoMet-dependent MTases, N6 of the adenine moiety is hydrogenbonded to the main chain carbonyl group of the histidine residue of the highly conserved motif III. Our studyreveals the evolutionary conservation of a carbonyl group in DNA, RNA and protein AdoMet-dependentMTases for specific interaction by hydrogen bond with AdoMet, despite the lack of overall sequenceconservation.

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