Streptococcus suis serotype 2 (SS2), a major swine pathogen and an emerging zoonotic agent, has greatly challenged global public health. The encoding
proteins with unknown functions the bacterium encodes are an obstruction to studies of the pathogenesis. A novel surface protective
antigen HP0197 is one of these
proteins which have no sequence homology to any known
protein. In the present study, the
protein was determined to be involved in bacterial virulence through an evaluation of the isogenic mutant (Δhp0197) in both mice and pigs. The experimental
infection also indicated that Δhp0197 could be cleared easily during
infection, which could be attributed to the reduced thickness of the capsular
polysaccharides (CPS) and the significantly reduced phagocytotic resistance. Microarrays-based comparative transcriptome analysis suggested that the suppressed expression of the operon responsible for CPS synthesis might be reversed by CcpA activity, which controlled global regulation of
carbon catabolite through the binding of the CcpA and HPr-Ser-46-P to the catabolite-responsive elements (cre) of the target operons. The hypothesis was approved by the fact that the purified FLAG-tagged HPr from WT
stain exhibited a higher binding activity to cre with CcpA compared to the Δhp0197 by the Electrophoretic Mobility Shift Assay, suggesting lower level of phosphorylation of the
phosphocarrier protein HPr at residue Ser-46 (HPr-Ser-46P) in Δhp0197. These indicated that HP0197 could enhance CcpA activity to control the expression of genes involved in
carbohydrate utilization and CPS synthesis, thus contributing to the virulence of S. suis.