Streptococcal M protein extracted by nonionic detergent. III. Correlation between immunological cross-reactions and
Abstract:
Three immunologically cross-reactive and non-cross-reactive streptococcal M proteins were analyzed by a chromatographic tryptic peptide mapping system. The results indicate that cross-reactions correlate with the extent of structural similarity among the M protein molecules analyzed. The data also reveal that free lysine is released by the action of trypsin from these three M proteins, suggesting a common lys-lys or arg-lys sequence. In addition, only one peptide has been found to be common within all three M types. This limited structural relatedness among the three M proteins examined indicates that sequence variation plays a major role in the immunological specificity of the M antigens. However, despite sequence variation, all M protein molecules have a common antiphagocytic activity. The fact that no common opsonic antibody has yet been found, even against limited M types, argues against this biological activity being solely the result of a common sequence. Based on these data, it is suggested that the antiphagocytic effect of M protein may be due to a conformationally created environment on the surface of the molecule which is selected by both immunological and biological pressure.
Insights
Streptococcal M protein cross-reactivity is linked to structural similarity. Despite sequence variations, M proteins share antiphagocytic activity, likely due to molecular surface conformation, not just common sequences.
Area of Science:
- Microbiology
- Immunology
- Protein Chemistry
Background:
- Streptococcal M proteins are key virulence factors.
- Immunological cross-reactivity between M proteins suggests structural similarities.
- Understanding M protein structure-function relationships is crucial for vaccine development.
Purpose of the Study:
- To analyze the structural basis of immunological cross-reactivity among streptococcal M proteins.
- To investigate the relationship between M protein structure and antiphagocytic activity.
- To identify common structural features contributing to M protein function.
Main Methods:
- Chromatographic tryptic peptide mapping was employed to analyze three M proteins.
- Analysis focused on identifying shared peptides and structural similarities.
- Enzymatic digestion with trypsin was used to probe protein sequences.
Main Results:
- Cross-reactions between M proteins correlated with structural similarity.
- A common lys-lys or arg-lys sequence was suggested by released free lysine.
- Limited shared peptides (one common peptide) were found among the three M types.
- Sequence variation was identified as a major factor in immunological specificity.
- All M proteins exhibited common antiphagocytic activity despite sequence differences.
Conclusions:
- Limited structural relatedness suggests sequence variation drives M antigen specificity.
- The common antiphagocytic activity may stem from a conformationally created surface environment.
- This conformational effect is likely shaped by both immunological and biological pressures.
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