IMMUNOCHEMICAL CHARACTERIZATION OF AN IGG-BINDING PROTEIN OF STREPTOCOCCUS-SUIS

Several bacterial species express surface proteins with affinity for t he constant region (F-c) of immunoglobulin (Ig) of different animal sp ecies. Previous studies from our group have reported the presence of a n IgG-binding protein in various serotypes of Streptococcus suis. This molecule was also shown to bind in a non-immune fashion chicken IgY a nd to our knowledge this characteristic is unique. In the present stud y, by dot-blotting, we showed that the native protein, obtained by aff inity chromatography, reacted more strongly with IgG from various anim al species than the denatured material. Using a competitive enzyme-lin ked immunosorbent assay the affinity of the native 60-kDa protein (pre viously identified as a 52-kDa protein) towards IgG of various animal species was compared to pig IgG. Bovine, goat and human IgG were able to compete effectively with pig Ige whereas chicken IgY constituted a poor competitor. Peptide mapping analysis using denatured protein indi cated that pig and bovine IgG recognized the same proteolytic fragment whereas chicken IgY did not. The smallest proteolytic fragment that r etained the binding activity towards the IgG of the different animal s pecies tested had a molecular mass of approximately 40 kDa. Fragments with M-r < 40 kDa showed specific binding activities. That is, the sma llest fragment binding pig and bovine IgG had a M-r of 30 kDa whereas for goat and human IgG a fragment of less than 16 kDa still showed bin ding activity. Finally, we observed that antisera raised against a hea t-shock protein of Pseudomonas aeruginosa reacted with the 60-kDa S. s uis protein indicating that the S. suis 60-kDa protein is a member of the 60-kDa hsp Family that possesses the characteristic of binding in a non-immune way mammalian IgG and chicken IgY. (C) 1998 Federation of European Microbiological Societies. Published by Elsevier Science B.V .