Immunological characterization and verification of recombinant streptococcal protein G

Streptococcal protein G (SPG), which is an antigen of the Streptococcus sp. cell wall, is important due to its high specificity to immunoglobulin (Ig), as compared with staphylococcal protein A. However, the cost of commercial recombinant (r)SPG has so far hindered further research into the application of rSPG. Efficient high cell density fermentation of genetically modified Escherichia coli and purification technology have previously been studied as a means to obtain rSPG. In the present study, the immunological characterization of purified rSPG was compared with commercial SPG via western blot analysis. The results of the present study demonstrated that the IgG‑binding capacity of purified rSPG was markedly higher, as compared with commercial SPG. Furthermore, purified rSPG cross‑linked with Q Sepharose® Fast Flow exhibited excellent affinity with IgG in murine serum. In order to obtain relatively pure and accurate rSPG, the purified rSPG was identified by Nanoflow Liquid Chromatography‑Mass Spectrometry (MS)/MS spectrum. The results indicated that the two peptide fragments of purified rSPG corresponded to the Streptococcus sp. GX7805 protein G as listed in the National Center for Biotechnology Information database. The method described in the present study offers a novel practical method for the verification of rSPG in relatively pure form, in order to purify IgG or carry out immunolabeling processes.