Epitope mapping of Streptococcus mutans SR protein and human IgG cross-reactive determinants, by using recombinant proteins and synthetic peptides.
alpha-Hemolytic oral streptococci are known to possess a family of cell surface cross-reactive proteins termed Ag I/II, having a molecular mass of approximately 180 to 210 kDa. These proteins are implicated in bacterial adherence to various oral tissues, and we showed recently that the SR protein, an I/II Ag-related protein, from Streptococcus mutans OMZ 175 serogroup f possesses Ag mimicry with human IgG. In this study, regions of the SR protein encoding the cross-reactive epitope(s) were analyzed by expressing selected restriction fragments from the cloned sr gene. The three SR-derived polypeptides reacted in ELISA with anti-SR rabbit IgG, whereas only the two polypeptides located along the carboxyl-terminal two thirds of the SR protein reacted with anti-human IgG rabbit IgG. In order to locate more precisely the human IgG-cross-reactive region, we synthesized six peptides, on the basis of the recently determined complete nucleotide sequence of the sr gene. Among these peptides, peptide 2, corresponding to the alanine-rich repeating amino-terminal region, peptide 3, located in the three tandem proline-rich regions, and peptide 6, located near the cell wall-spanning region, were the most interesting in term of antigenicity and immunogenicity. Anti-peptide 2, 3, and 6 rabbit IgG reacted with free SR and with cell wall-associated SR. Peptide 1, located near the amino terminus, was poorly immunogenic. Peptides 4 and 5, located in the putative human IgG-cross-reactive region, were immunogenic; however, anti-peptide 4 rabbit IgG reacted only weakly with SR or human IgG, whereas anti-peptide 5 rabbit IgG reacted strongly with SR and human IgG, and peptide 5 was recognized by anti-SR and anti-human IgG rabbit IgG. These results confirm the cell surface accessibility of this epitope and its potential participation in eliciting, in rabbits, anti-SR IgG cross-reactive with human IgG.
Gangloff
S
S
National Institute of Health and Medical Research U157, Faculty of Dentistry, Srasbourg, France.
M'Zoughi
R
R
Lett
E
E
Scholler
M
M
Baer
J
J
Pini
A
A
Ogier
J
J
Klein
J P
JP
D000595:Amino Acid Sequence; D000907:Antibodies, Bacterial / Q000032:analysis; D001426:Bacterial Proteins / Q000276:immunology*; D003429:Cross Reactions; D000939:Epitopes / Q000032:analysis*; D006801:Humans; D007114:Immunization; D007074:Immunoglobulin G / Q000276:immunology*; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000276:immunology*; D011994:Recombinant Proteins / Q000276:immunology; D013295:Streptococcus mutans / Q000276:immunology*
D000907:Antibodies, Bacterial; D001426:Bacterial Proteins; D000939:Epitopes; D007074:Immunoglobulin G; D010446:Peptide Fragments; D011994:Recombinant Proteins; C063999:SR protein, bacteria