Construction of the pore-forming toxin gene exlA knock-out mutant of Pseudomonas aeruginosa and its basic characteristics / 军事医学

Objective To construct a non-trace deletion mutant of exlA in Pseudomonas aeruginosa strain NY8755(NY8755ΔexlA)and investigate the basic characteristics of pore-forming toxin ExlA.Methods The NY8755ΔexlA was constructed using the secondary homologous recombination method.C57BL/6J female mice ages 6 to 8 weeks were infected with NY8755 and NY8755 ΔexlA via aerosolized intratraheal inoculation respectively.Within 7 days of infection,the survival and weight changes of the mice were observed and recorded before the proinflammatory cytokines in the bronchoal-veolar lavage fluid(BALF)of the infected mice in the two groups were detected.Results The sequencing results showed that NY8755 ΔexlA was constructed.After 1×107 CFU NY8755 and NY8755 ΔexlA were infected,all the mice in the wild-type strain group died within 48 hours,while those in the mutant strain group began to die after 48 hours,and 40%of them remained alive 7 days later.The weight of surviving mice in the mutant strain group decreased but recovered gradually.After 12 hours of infection,there were more bloody exudates(redder in color)in the BALF of the wild-type strain group than in the mutant strain group,and the contents of proinflammatory cytokines interleukin-1β(IL-1β)and interleukin-17A (IL-17A)were significantly different. Conclusion Pseudomonas aeruginosa pore-forming toxin ExlA is the key pathogenic virulence factor of the exlA-positive Pseudomonas aeruginosa,which can significantly affect the survival status of mice and cause obvious inflammation in mice. Very little information is available on the action mechanisms of ExlA. In this study, The NY8755ΔexlA and the C57BL/6J mouse models infected with NY8755 and NY8755ΔexlA have been constructed that may be used for the investigation of pathogenesis of exlA-positive Pseudomonas aeruginosa.

Generation of dimeric single-chain antibodies neutralizing the cytolytic activity of vaginolysin

Background: Gardnerella vaginalis is a bacterial vaginosis (BV)-associated vaginal bacterium that produces the toxin vaginolysin (VLY). VLY is a pore-forming toxin that is suggested to be the main virulence factor of G. vaginalis. The high recurrence rate of BV and the emergence of antibiotic-resistant bacterial species demonstrate the need for the development of recombinant antibodies as novel therapeutic agents for disease treatment. Single-chain variable fragments (scFvs) generated against VLY exhibited reduced efficacy to neutralize VLY activity compared to the respective full-length antibodies. To improve the properties of scFvs, monospecific dimeric scFvs were generated by the genetic fusion of two anti-VLY scFv molecules connected by an alpha-helix-forming peptide linker. Results: N-terminal hexahistidine-tagged dimeric scFvs were constructed and produced in Escherichia coli and purified using metal chelate affinity chromatography. Inhibition of VLY-mediated human erythrocyte lysis by dimeric and monomeric scFvs was detected by in vitro hemolytic assay. The circulating half-life of purified scFvs in the blood plasma of mice was determined by ELISA. Dimeric anti-VLY scFvs showed higher neutralizing potency and extended circulating half-life than parental monomeric scFv. Conclusions: The protein obtained by the genetic fusion of two anti-VLY scFvs into a dimeric molecule exhibited improved properties in comparison with monomeric scFv. This new recombinant antibody might implement new possibilities for the prophylaxis and treatment of the diseases caused by the bacteria G. vaginalis.

The membranotropic activity of N-terminal peptides from the pore-forming proteins sticholysin I and II is modulated by hydrophobic and electrostatic interactions as well as lipid composition.

The sea anemone Stichodactyla helianthus produces two pore-forming proteins, sticholysins I and II (St I and St II). Despite their high identity (93%), these toxins exhibit differences in hemolytic activity that can be related to those found in their N-terminal. To clarify the contribution of the N-terminal amino acid residues to the activity of the toxins, we synthesized peptides spanning residues 1–31 of St I (StI1-31) or 1–30 of St II (StII1-30) and demonstrated that StII1-30 promotes erythrocyte lysis to a higher extent than StI1-31. For a better understanding of the molecular mechanism underlying the peptide activity, here we studied their binding to lipid monolayers and pemeabilizing activity in liposomes. For this, we examined the effect on peptide membranotropic activity of including phospatidic acid and cholesterol in a lipid mixture of phosphatidylcholine and sphingomyelin. The results suggest the importance of continuity of the 1–10 hydrophobic sequence in StII1-30 for displaying higher binding and activity, in spite of both peptides’ abilities to form pores in giant unilamellar vesicles. Thus, the different peptide membranotropic action is explained in terms of the differences in hydrophobic and electrostatic peptide properties as well as the enhancing role of membrane inhomogeneities.

Purification of a 19-kDa pore-forming cytolysin from the sea anemone Heteractis magnifica

Pore-forming cytolysins of 19 kDa from sea anemones present a remarkable cytolytic property. In the present work, a purified 19-kDa cytolysin was obtained from the sea anemone Heteractis magnifica. The purification steps involved ammonium sulfate precipitation and subsequently desalting by dialysis against 10 mM sodium phosphate buffer (pH 7.4), followed by anion exchange chromatography in DEAE-Sepharose® column (GE Healthcare, Sweden) and gel filtration chromatography using Sephadex® G-50 matrix (GE Healthcare, Sweden). The active fractions from the gel filtration chromatography were pooled and rechromatographed in the same column. The final active fraction showed a prominent protein band of molecular mass of 19 kDa when analyzed by SDS-PAGE.(AU)