Identification of a conserved B-cell epitope on the GapC protein of Streptococcus dysgalactiae

• The mAb1F2 against Streptococcus dysgalactiae GapC was successfully generated.
• The motif 30TRINDLT36 is an epitope of the S. dysgalactiae GapC.
• Our findings are available for further study of epitope-based vaccines.

Streptococcus dysgalactiae (S. dysgalactia) GapC is a highly conserved surface dehydrogenase among the streptococcus spp., which is responsible for inducing protective antibody immune responses in animals. However, the B-cell epitope of S. dysgalactia GapC have not been well characterized. In this study, a monoclonal antibody 1F2 (mAb1F2) against S. dysgalactiae GapC was generated by the hybridoma technique and used to screen a phage-displayed 12-mer random peptide library (Ph.D.-12) for mapping the linear B-cell epitope. The mAb1F2 recognized phages displaying peptides with the consensus motif TRINDLT. Amino acid sequence of the motif exactly matched 30TRINDLT36 of the S. dysgalactia GapC. Subsequently, site-directed mutagenic analysis further demonstrated that residues R31, I32, N33, D34 and L35 formed the core of 30TRINDLT36, and this core motif was the minimal determinant of the B-cell epitope recognized by the mAb1F2. The epitope 30TRINDLT36 showed high homology among different streptococcus species. Overall, our findings characterized a conserved B-cell epitope, which will be useful for the further study of epitope-based vaccines.