ABSTRACT
Objective To analyze the enzymatic properties of alkyl hydroperoxide reductase sub-unit C (AhpC) from Leptospira interrogans (L.interrogans) and to elucidate its physiological roles in host-pathogen interactions in macrophages during Leptospira infection. Methods A prokaryotic expression system for ahpC gene of L.interrogans serogroup Icterohaemorrhagiae serovar Lai strain Lai was established to ex-press the recombinant AhpC(rAhpC). After purified by Ni-NTA affinity chromatography,the enzymatic ac-tivity of the rAhpC and its role in protecting DNA from oxidation were analyzed. The importance of each cys-teine in its molecule was evaluated through site-directed mutation. L.interrogans strains were pretreated with or without Conoidin A, a covalent inhibitor of peroxiredoxin, and then were used to infect macrophages. Changes in oxidative status in leptospires and survival rates of L.interrogans strains were analyzed by fluores-cence-activated cell sorting and colony counting method. Results The rAhpC was successfully expressed in the established prokaryotic expression system. It had peroxiredoxin activity that was able to catalyze the re-duction of hydrogen peroxide. Its ability of reducing hydrogen peroxide depended on the thioredoxin/thiore-doxin reductase system. Cys47 (a peroxidatic cysteine) and Cys167 (a resolving cysteine) were critical to maintaining the enzymatic activity of AhpC. AhpC could protect DNA from hydrogen peroxide induced-oxida-tive damage. When L.interrogans strains were pretreated with Conoidin A,the oxidative status in leptospires was elevated and the survival of L.interrogans in macrophages was significantly reduced in a dose-dependent manner. Conclusion The AhpC of L.interrogans is a thioredoxin-dependent peroxiredoxin that plays an im-portant role in protecting L.interrogans against oxidative stress in macrophages.
ABSTRACT
objective To determine the existence of virulence-associated invA gene in different genospeeies of Leptospira interrogans reference strains in China.and to understand the alterations of invA gene transcription and expression of L.interrogans strain Lai before or after infecting cells.Methods PCR was applied to detect the invA gene of four L.interrogans strains belonging to four different genospecies and L.biflexa strain Patoc Ⅰ.The entire invA genes from the L.interrogans strains were cloned and then sequenced.The prokaryotic expression system of invA gene of L.interrogans serogroup Icterohaemorrhagiae serovar Lai strain Lai was constructed.Using Ni-NTA affinity chromatography,the target recombinant protein rInvA was extracted and purified.Rabbits were immunized with rInvA to obtain antiserum and the titer of antiserum was determined by immunodiffusion test.A model of L interrogans strain Lai infecting human embryo kidney cell line HEK293 was established to detect the alterations of invA gene transcription and expression of the leptospiral strain before or after infecting the host cells by real-time fluorescent quantitative RTPCR and western blot assay.Results All the four tested L.interrogans strains had invA gene whereas L.biflexa strain Patoc Ⅰ not.The similarity of nucleotide and putative amino acid sequences of invA genes from the four L.interrogans strains belonging four different genospecies were 99.33%-100%and 98.66%-100%,respectively.The constructed prokaryotic expression system could efficiently express rInvA and the immunodiffusion titer of rabbit anti-rInvA serum was 1:16.After L.interrogans strain Lai infecting HEK293 cells for 30 min or above,the microbe could adhere the surface of the cells.On the 30 min after the infection,the mRNA level of invA gene of L.interrogans strain Lai was remarkably upregulated,and on the 45 min after infection the mRNA level presented a peak value and then graduated decreased.On the 45 min or 60 min after L.interrogans strain Lai infecting HEK293 cells,InvA protein could be detectable but before infection or after infection for over 90 min the InvA protein expression was negative.Conclusion The invA gene is a unique gene for pathogenic L.interrogans.The invA gene of L interrogans has characteristics of cell-touched expression and transient expression,which may have a close correlation with adhering and invading host cells.
ABSTRACT
Objective To screen the efficient antigenic epitopes in genus-specific envelope proteins OmpL1 and LipL21 of Leptospira interrogans for further development of multiple antigenic peptide (MAP)vaccine.Methods Based on bioinformatic technique,the combined epitopes of T and B lymphcytes in OmpL1 and LipL21 molecules were screened.Nucleotide fragments of each epitopes were amplified by PCR and then constructed their phage display systems.Using antisera against rOmpL1,rLipL21,L.interrogans serogroup Icterohaemorrhagiae strain Lai and leptospirosis patients' sera as the first antibodies.respectively,Western blot assays were performed to determine the immunoreaetivity and reactive ability of the epitopes with different antisera.Resuits Four combined epitopes of OmpL1 and two combined epitopes of LipL21 were selected out by the predicting procedure.All the amplified epitope fragments were accurately inserted into the region at N end of phage PⅢ protein and successfully expressed.All of the antisera could recognize each of the epitopes.Based on the results of Western blot,the two LipL21 epitopes at 97-112 and 176-184 showed similar strong hybridization signals with any of the antisera,and the hybridization signals of four OmpL1 epitopes with the three antisera were 173-191,87-98,297-320 and 59-78,from strong to weak.Conclusion The six combined epitopes in this study are efficiently antigenic.And the epitopes at positions 97-112 and 176-184 in LipL21 as well as the epitopes at position 87-98 and 173-191 in OmpL1 have a potential for developing leptospiral MAP vaccine.