Preparation of a fusion protein with pneumococcal surface protein A of two different clades of familyⅠand analysis of immunogenicity of the recombinant protein / 中华微生物学和免疫学杂志

ABSTRACT

Objective To construct a recombinant fusion protein with pneumococcal surface pro-tein A (PspA) of Stretococcus pneumonia (SPN) familyⅠclade 1 and 2, and to analyze the immunogenici-ty of the fusion protein.Methods The gene fragments encoding theα-helix of PspA of the two clades were amplified by PCR and then inserted into the expression vector pET-27b(+) to construct the recombinant ex-pression plasmid.The transformed Escherichia coli BL21 strains carrying expression plasmid were induced by IPTG to express the recombinant protein.The titers and affinity of antibodies against PspA protein were measured by ELISA.An opsonophagocytic assay and an animal experiment were performed to evaluate the immunogenicity of the recombinant protein.Results Double enzyme cutting and gene sequencing confirmed the two purpose gene fragments were correctly expressed in the expression vector pET-27b(+).The titers of anti-PspA antibody in the serum of Kunming ( KM) mice immunized with the fusion protein were 1 ×104 . The affinity of anti-PspA antibody reached to 2×105 .The rates of recombinant PspA6B-PspA05 protein me-diated phagocytosis for SPN6B, SPN05 and SPN01 strains were 20%, 15% and 8.8%, respectively.No SPN23F strain was engulfed by macrophages upon the stimulation with PspA6B-PspA05 protein.The survival rates of mice injected with SPN05, SPN6B, SPN01 and SPN23F strains were respectively 75%, 92%, 75%and 33%upon the immunization of PspA6B-PspA05 protein.Conclusion The recombinant fusion protein PspA6B-PspA05, constructed with the PspA proteins of Stretococcus pneumonia familyⅠclade 1 and 2, was successfully expressed in the E.coli prokaryotic system with the advantage of high immunogenicity.High ti-ters of anti-PspA antibodies with high specificity were induced in KM mice upon the stimulation with Ps-pA6B-PspA05 protein.Moreover, a cross-protective immunity was induced in KM mice upon the immuniza-tion with PspA6B-PspA05 protein.