INVESTIGATING THE ANTIGENICITY OF A RECOMBINANT PROTEIN FROM STREPTOCOCCUS SUIS

Abstract

Streptococcus suis serotype 2 (S. suis 2) is a zoonotic infectious pathogen associated with a wide range of diseases in humans and pigs. This project aims to study the antigenicity of glutamate dehydrogenase (gdh) recombinant protein as a molecular diagnostic marker for S. suis infection. In order words, the objective is to express fragment of glutamate dehydrogense (gdh) of S. suis 2 and analyze its protein’s immunological activity for its application as antigen candidate. The gdh DNA fragment was amplified from genomic DNA of a pathogenic S. suis 2 (strain 31533) genomic DNA by DNA amplification. The DNA fragment was inserted into both of the cloning vector pET-30a and pET-SUMO and both recombinant plasmids were individually transformed into competent E. coli BL21 (DE3) cells for expression under IPTG induction. The recombinant protein was purified by Ni-NTA affinity chromatography. The immunological activity of the purified recombinant protein was investigated by either immunizing rabbit using ELISA assay or immunoblotting method. The expected 1056bp PCR product was obtained. Following our prediction, the target protein could be approximately expressed up to 80% (GDH-SUMO) and 20% (GDH-pET30a) of total crude protein. The purity of protein reached more than 80% after purification in denaturing condition. The GDH recombinant protein, which was employed to detect S. suis infection, showed to be a non-specific antigen in ELISA test. However, GDH protein could be considered as a potential diagnostic marker due to the distinguishing with Streptococcus pneumoniae which is mainly misdiagnose with S. suis 2. Key words: Streptococcus suis, glutamate dehydrogenase gene, antigenicity, pET30a, pET-SUMO