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Studies on group A streptococcal M-proteins: purification of type 5 M-protein and comparison of its amino terminal
Abstract:
M-protein was isolated from group A, type 5, streptococci by limited proteolysis with pepsin and purified by chromatography on DEAE-Sephadex followed by gel filtration. The protein thus purified (Pep M5) was homogeneous by SDS-polyacrylamide gradient gel electrophoresis (apparent m.w.: 19,000), retained the capacity to remove opsonic antibodies from type 5 antiserum, and was capable of eliciting opsonic antibodies in rabbits. Its amino acid composition was very similar to that reported for M-proteins from other streptococcal types. The sequence of the first 29 amino terminal residues of Pep M5 was determined and compared with the reported amino terminal sequences of two immunologically unrelated M-proteins, namely, Pep M6 and Pep M24. The results revealed that, although the amino terminal sequences fo these three proteins differed from each other, some amino acid residues appeared to be conserved, suggesting a certain degree of structural relatedness among these M molecules. The possibility that this feature forms the molecular basis for the common antiphagocytic behavior of immunologically unrelated M-proteins is discussed.
Insights
Researchers isolated and purified M-protein (Pep M5) from group A, type 5, streptococci. Structural analysis revealed conserved amino acid residues, suggesting relatedness among M-proteins and explaining their common antiphagocytic function.
Area of Science:
- Microbiology
- Immunology
- Structural Biology
Background:
- M-proteins are surface proteins of group A Streptococcus.
- These proteins are crucial for bacterial virulence, particularly their antiphagocytic properties.
- Understanding M-protein structure is key to developing effective vaccines and treatments.
Purpose of the Study:
- To isolate and purify M-protein from group A, type 5, streptococci (Pep M5).
- To characterize the biochemical and structural properties of Pep M5.
- To compare the amino-terminal sequence of Pep M5 with other M-proteins to identify conserved regions and understand structure-function relationships.
Main Methods:
- Limited proteolysis with pepsin for M-protein isolation.
- Chromatography (DEAE-Sephadex) and gel filtration for purification.
- SDS-polyacrylamide gradient gel electrophoresis for homogeneity assessment.
- Amino-terminal sequencing.
Main Results:
- Homogeneous Pep M5 (apparent m.w.: 19,000) was obtained.
- Pep M5 retained opsonic antibody-removing capacity and elicited opsonic antibodies.
- Amino acid composition was similar to other M-proteins; amino-terminal sequencing revealed conserved residues despite sequence differences among Pep M5, Pep M6, and Pep M24.
Conclusions:
- The study successfully isolated and characterized Pep M5, confirming its functional and structural characteristics.
- Conserved amino acid residues in the amino-terminal sequences suggest an underlying structural relatedness among immunologically distinct M-proteins.
- This structural relatedness may explain the shared antiphagocytic function of various M-proteins, offering insights into Streptococcus pathogenesis.