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Molecular characterization of the gene sr of the saliva interacting protein from Streptococcus mutans OMZ175
J A Ogier1, D Wachsmann, M Schöller
1Unité INSERM U 157, Faculté de chirurgie dentaire, Strasbourg, France.
Abstract:
The saliva interacting protein (74KSR) from Streptococcus mutans serotype f, which is immunologically related to antigen I/II from serotype c, also termed B, P1, PAc, is probably involved in the adherence process of Strep. mutans to the tooth surface. A solid-phase adherence assay showed that 38% of the binding of salivary glycoproteins to Strep. mutans OMZ175 was due to this protein. We have cloned and sequenced the 74KSR gene (sr), which produces a recombinant protein (rec195K) with a relative molecular mass of 195,000, as estimated by SDS-PAGE. The strong immunological relationship and functional identity of the 74KSR and rec195K indicate that the Mr 195K protein is probably a precursor form, post-translationally processed, of the 74KSR produced in Strep. mutans. The gene sr consists of 4667 bp and codes for a 171,177 Mr protein. Biochemical features of the protein (density in proline residues and hydrophobicity) may explain the difference observed between the SDS-PAGE estimated molecular mass of the immature protein and the one deduced from the nucleotide sequence. Intra-species hybridization experiments using three contiguous restriction fragments isolated from gene sr as probes showed that the sequence is highly similar in strains from serotypes c and e. We have also shown that a fraction of the heart specific antibodies induced in rabbits during immunization with the 74KSR or rec195K reacts predominantly with human IgG and suggest the hypothesis of antigen mimicry as an explanation for the production of anti-IgG autoantibodies. It will be of great importance to identify the cross-reactive epitopes within the molecule before considering its use in protective immunization against oral streptococci.
Insights
The Streptococcus mutans 74KSR protein aids bacterial adherence to teeth. Its gene sequence suggests a precursor form, with implications for understanding oral streptococcal infections and potential immunization strategies.
Area of Science:
- Microbiology
- Molecular Biology
- Immunology
Background:
- Streptococcus mutans adheres to teeth, contributing to oral health issues.
- The saliva interacting protein (74KSR) is implicated in Streptococcus mutans adherence.
- 74KSR is immunologically related to antigen I/II (B, P1, PAc) from other serotypes.
Purpose of the Study:
- To clone and sequence the gene encoding 74KSR.
- To characterize the recombinant protein and its relationship to the native protein.
- To investigate the prevalence of the gene in different serotypes and explore potential immunological cross-reactivity.
Main Methods:
- Solid-phase adherence assay to quantify protein binding.
- Gene cloning and nucleotide sequencing of the 74KSR gene (sr).
- SDS-PAGE for molecular mass estimation.
- Nucleotide sequence analysis and intra-species hybridization.
- Antibody production in rabbits and analysis of cross-reactivity with human IgG.
Main Results:
- 38% of salivary glycoprotein binding to Strep. mutans OMZ175 was attributed to 74KSR.
- The 74KSR gene (sr) was cloned and sequenced, revealing a coding sequence for a 171,177 Mr protein.
- A recombinant protein (rec195K) showed immunological and functional identity with 74KSR, suggesting a precursor relationship.
- The sr gene sequence is highly conserved in serotypes c and e.
- Antibodies against 74KSR/rec195K cross-reacted with human IgG, suggesting antigen mimicry.
Conclusions:
- The Mr 195K protein is likely a precursor to the 74KSR found in Streptococcus mutans.
- Biochemical properties may explain discrepancies in molecular mass estimations.
- The high sequence similarity across serotypes suggests a conserved function.
- Antigen mimicry may explain autoantibody production, necessitating epitope identification for safe immunization strategies against oral streptococci.