Recently, we generated two bacterial recombinant proteins expressing 89 amino acids of the C-terminal domain of the Plasmodium vivax merozoite surface protein-1 and the hexa-histidine tag (His6MSP1(19)). One of these recombinant proteins contained also the amino acid sequence of the universal pan allelic T-cell epitope (His6MSP1(19)-PADRE). In the present study, we evaluated the immunogenic properties of these antigens when administered via the intra-nasal route in the presence of distinct adjuvant formulations. We found that C57BL/6 mice immunized with either recombinant proteins in the presence of the adjuvants cholera toxin (CT) or the Escherichia coli heat labile toxin (LT) developed high and long lasting titers of specific serum antibodies. The induced immune responses reached maximum levels after three immunizing doses with a prevailing IgG1 subclass response. In contrast, mice immunized by intranasal route with His6MSP1(19)-PADRE in the presence of the synthetic oligonucleotides adjuvant CpG ODN 1826 developed lower antibody titers but when combined to CT, CpG addition resulted in enhanced IgG responses characterized by lower IgG1 levels. Considering the limitations of antigens formulations that can be used in humans, mucosal adjuvants can be a reliable alternative for the development of new strategies of immunization using recombinant proteins of P. vivax.

Attempts to obtain a recombinant protein using prokaryotic expression systems can go from a rewarding and rather fast procedure to a frustrating time-consuming experience. In most cases production of heterologous proteins in Escherichia coli K12 strains has remained an empirical exercise in which different systems are tested without a careful insight into the various factors affecting adequate expression of the encoded protein. The present review will deal with E. coli as protein factory and will cover some of the aspects related to transcriptional and translational expression signals, factors affecting protein stability and solubility and targeting of proteins to different cell compartments. Based on the knowledge accumulated over the last decade, we believe that the rate of success for those dedicated to expression of recombinant proteins based on the use E. coli strains can still be significantly improved.

Mutantes de Escherichia coli resistentes aos aminoglicosídios por seleção in vitro em meio de cultivo de alta osmolaridade contendo canamicina podem apresentar ausência da proteína periplásmica oligopeptídio permease (OppA). O comportamento desse mutante em presença de canamicina ou do peptídio tóxico triornitina sugere que a proteína OppA e um outro componente do envoltório bacteriano contribuem para a resistência osmodependente em E. coli.

The oligopeptide permease (OppA) protein was found to be missing in the periplasmic fractions of Escherichia coli kanamycin-resistant mutants selected under high osmotic conditions. The growth behavior of one mutant in media containing kanamycin or the toxic peptide triornithine suggests that OppA and another cell envelope component contribute to the osmolarity-dependent aminoglycoside resistance of E. Coli.