assessing n-terminal region of pneumococcal choline-binding protein d as a vaccine candidate targeting streptococcus pneumoniae

Background: streptococcus pneumoniae is a major cause of pneumonia and meningitis, particularly in children under five years of age. the limited serotype coverage and high cost of pneumococcal conjugate vaccines highlight the need for affordable, serotype-independent vaccine candidates. choline-binding protein d (cbpd), a surface protein involved in pneumococcal virulence, represents a promising antigenic target. this study aimed to evaluate the immunogenic potential of the n-terminal fragment of cbpd (fcbpd) from s. pneumoniae serotype 19f as a candidate for protein-based pneumococcal vaccines.materials and methods: the fcbpd gene encoding amino acids 51–353 was cloned into the pet28a vector and expressed in escherichia coli bl21 (de3). bioinformatics analyses were performed to assess protein stability, antigenicity, and epitope prediction. the recombinant protein was purified under denaturing conditions and refolded. balb/c mice were immunized with fcbpd in combination with flagellin as an adjuvant, and specific igg responses were measured by elisa.results: sequence analysis demonstrated high conservation (>94%) of fcbpd among major invasive pneumococcal serotypes. bioinformatics tools confirmed its stability and antigenicity, with three conformational b-cell epitopes identified. the recombinant protein was successfully expressed (~34 kda) and purified. immunization with fcbpd plus flagellin induced a significant increase in specific igg levels compared to control groups (p<0.05), indicating strong immunogenicity.conclusion: fcbpd is a conserved and immunogenic antigen capable of inducing a specific antibody response, supporting its potential as a serotype-independent candidate for pneumococcal vaccine development.