ABSTRACT
We have isolated a full-length cDNA encoding an acetylcholinesterase secreted by the nematode parasite Nippostrongylus brasiliensis. The predicted protein is truncated in comparison with acetylcholinesterases from other organisms such that the carboxyl terminus aligns closely to the end of the catalytic domain of the vertebrate enzymes. The residues in the catalytic triad are conserved, as are the six cysteines which form the three intramolecular disulfide bonds. Three of the fourteen aromatic residues which line the active site gorge in the Torpedo enzyme are substituted by nonaromatic residues, corresponding to Tyr-70 (Thr), Trp-279 (Asn), and Phe-288 (Met). High level expression was obtained via secretion from Pichia pastoris. The purified enzyme behaved as a monomeric hydrophilic species. Although of invertebrate origin and possessing the above substitutions in the active site gorge residues, the enzyme efficiently hydrolyzed acetylthiocholine and showed minimal activity against butyrylthiocholine. It displayed excess substrate inhibition with acetylthiocholine at concentrations over 2. 5 mM and was highly sensitive to both active site and "peripheral" site inhibitors. Northern blot analysis indicated a progressive increase in mRNA for AChE B in parasites isolated from 6 days postinfection.
Subject(s)
Acetylcholinesterase/genetics , Nippostrongylus/enzymology , Acetylcholinesterase/chemistry , Acetylcholinesterase/metabolism , Amino Acid Sequence , Animals , Base Sequence , Caenorhabditis elegans/enzymology , Cholinesterase Inhibitors/pharmacology , Cloning, Molecular , DNA, Complementary/chemistry , Gene Expression Regulation, Enzymologic , Intestine, Small/parasitology , Male , Molecular Sequence Data , Pichia/enzymology , Rats , Rats, Sprague-Dawley , Sequence Alignment , Strongylida Infections/enzymology , Strongylida Infections/parasitology , Substrate Specificity , TorpedoABSTRACT
Expression plasmids encoding the hypoxanthine phosphoribosyltransferases (HPRTs) of Plasmodium falciparum, Schistosoma mansoni, Tritrichomonas foetus, and Homo sapiens were subcloned into genetically deficient Escherichia coli that requires complementation by the activity of a recombinant HPRT for growth on semidefined medium. Fifty-nine purine analogs were screened for their abilities to inhibit the growth of these bacteria. Several compounds that selectively altered the growth of the bacteria complemented by the malarial, schistosomal, or tritrichomonal HPRT compared with the growth of bacteria expressing the human enzyme were identified. These results demonstrate that the recombinant approach to screening compounds by complement selection in a comparative manner provides a rapid and efficient method for the identification of new lead compounds selectively targeted to the purine salvage enzymes of parasites.
Subject(s)
Escherichia coli/genetics , Plasmodium falciparum/enzymology , Purines/metabolism , Schistosoma mansoni/enzymology , Tritrichomonas foetus/enzymology , Animals , DNA, Bacterial/metabolism , DNA, Complementary/metabolism , Escherichia coli/enzymology , Escherichia coli/metabolism , Genetic Complementation Test , Humans , Hypoxanthine Phosphoribosyltransferase/biosynthesis , Hypoxanthine Phosphoribosyltransferase/genetics , Hypoxanthine Phosphoribosyltransferase/metabolism , Plasmids , Plasmodium falciparum/genetics , Schistosoma mansoni/genetics , Tritrichomonas foetus/geneticsABSTRACT
Candida albicans yeast cells H317 were grown to mid-log phase, mechanically disrupted and the resulting crude extract clarified by centrifugation. This catalase rich fraction (1.26 x 10(-4) units/ml) was fractionated by liquid phase isoelectric focusing in a pH gradient ranging from 3 to 10 using the Rotofor Isoelectric Focusing Preparative Cell. After isoelectric separation, fractions containing catalase activity were focused between pH 6.7 and 9.3. Active fractions were pooled and re-focused. After the second fractionation, catalase activity increased to 1.52 x 10(-2) units/ml and was restricted to fractions ranging from pH 7.6 to 8.8. To this point a 121 fold purification was achieved. Native polyacrylamide gel electrophoresis analysis of active fractions revealed a band migrating between 272,000 and 132,000 daltons which showed catalase activity. Purification of C. albicans catalase will allow us to evaluate its potential role in protecting this opportunistic pathogen from products of the oxidative burst. Antibodies generated against the catalase provide means for the evaluation of neutralizing fungal defenses against products of the oxidative burst during phagocytosis.
Subject(s)
Candida albicans/enzymology , Catalase/isolation & purification , Cells, Cultured , Electrophoresis, Polyacrylamide Gel , Isoelectric FocusingABSTRACT
Candida albicans yeast cells H317 were grown to mid-log phase, mechanically disrupted and the resulting crude extract clarified by centrifugation. This catalase rich fraction (1.26 x 10(-4) units/ml) was fractionated by liquid phase isoelectric focusing in a pH gradient ranging from 3 to 10 using the Rotofor Isoelectric Focusing Preparative Cell. After isoelectric separation, fractions containing catalase activity were focused between pH 6.7 and 9.3. Active fractions were pooled and re-focused. After the second fractionation, catalase activity increased to 1.52 x 10(-2) units/ml and was restricted to fractions ranging from pH 7.6 to 8.8. To this point a 121 fold purification was achieved. Native polyacrylamide gel electrophoresis analysis of active fractions revealed a band migrating between 272,000 and 132,000 daltons which showed catalase activity. Purification of C. albicans catalase will allow us to evaluate its potential role in protecting this opportunistic pathogen from products of the oxidative burst. Antibodies generated against the catalase provide means for the evaluation of neutralizing fungal defenses against products of the oxidative burst during phagocytosis
