RESUMEN
Pseudomonas aeruginosa exotoxin A (PEA) is a number of family of bacterial ADP-ribosylating toxins and possesses strong immunogenicity. The detoxified exotoxin A, as a potent vaccine adjuvant and vaccine carrier protein, has been extensively used in human and animal vaccinations. However, the expression level of PEA gene in Escherichia coli is relative low which is likely due to the presence of rare codon and high levels of GC content. In order to enhance PEA gene expression, we optimized PEA gene using E. coli preferred codons and expressed it in E. coli BL21 (DE3) by using pET-20b(+) secretory expression vector. Our results showed that codon optimization significantly reduced GC content and enhanced PEA gene expression (70% increase compared with that of the wild-type). Moreover, the codon-optimized PEA possessed biological activity and had the similar toxic effects on mouse L292 cells compared with the wild-type PEA gene. Codon optimization will not only improve PEA gene expression but also benefit further modification of PEA gene using nucleotide-mediated site-directed mutagenesis. A large number of purified PEA proteins will provide the necessary conditions for further PEA functional research and application.
Asunto(s)
ADP Ribosa Transferasas/genética , ADP Ribosa Transferasas/aislamiento & purificación , Toxinas Bacterianas/genética , Toxinas Bacterianas/aislamiento & purificación , Clonación Molecular/métodos , Escherichia coli/genética , Exotoxinas/genética , Exotoxinas/aislamiento & purificación , Regulación Bacteriana de la Expresión Génica , Pseudomonas aeruginosa/genética , Factores de Virulencia/genética , Factores de Virulencia/aislamiento & purificación , ADP Ribosa Transferasas/metabolismo , Secuencia de Aminoácidos , Toxinas Bacterianas/metabolismo , Línea Celular , Supervivencia Celular , Codón/genética , Exotoxinas/metabolismo , Genes Bacterianos , Datos de Secuencia Molecular , Pseudomonas aeruginosa/metabolismo , Proteínas Recombinantes/genética , Proteínas Recombinantes/aislamiento & purificación , Proteínas Recombinantes/metabolismo , Factores de Virulencia/metabolismo , Exotoxina A de Pseudomonas aeruginosaRESUMEN
Sterile, concentrated culture supernatant from Pasteurella haemolytica (biotype A, serotype 1) strain 630 was subjected to physical, chemical, and immunologic treatments to determine their influence on leukotoxin (cytotoxin) activity contained in the supernatant. Each treated sample contained approximately 8 chemiluminescence inhibitory units of leukotoxin. Treatment effects were evaluated for their ability to inactivate leukotoxin activity. Leukotoxin activity in treated samples was determined by inhibition of the luminol-dependent chemiluminescence response of bovine neutrophils. Optimal leukotoxin synthesis by P haemolytica occurred when the bacteria were at the logarithmic growth phase, whereas stationary phase cultures contained minimal amounts of leukotoxin activity in their culture supernatant. Leukotoxin activity was heat labile; activity was substantially decreased when concentrated culture supernatant samples containing leukotoxin activity were incubated at 37 C for several hours. When concentrated culture supernatant was incubated at progressively decreasing temperatures, there was a progressive increase in the length of time that the leukotoxin retained its biologic activity. Samples stored at -70 C retained activity for at least 2 months. Leukotoxin activity was nondialyzable and was able to withstand considerable extremes in hydrogen ion concentration. Leukotoxin activity could not be pelleted when subjected to forces of 100,000 X g for 1 hour. Chemical and enzymatic studies suggested that P haemolytica leukotoxin contained carbohydrate and protein moieties. Chemical treatment with 0.2% sodium lauryl sulfate, 0.5% sodium deoxycholate, 7.5 mM EDTA and 8M urea with 8 mM 2-mercaptoethanol and enzymatic treatment with lipase, ribonuclease, and deoxyribonuclease had no discernible effect on leukotoxin activity.(ABSTRACT TRUNCATED AT 250 WORDS)