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Complete amino acid sequence of streptococcal PepM49 protein, a nephritis-associated serotype. Conserved
K M Khandke1, T Fairwell, A S Acharya
1Rockefeller University, New York, New York 10021.
Abstract:
The complete amino acid sequence of PepM49, a peptic fragment of the group A streptococcal type 49 M protein, the antiphagocytic cell surface molecule of the bacteria, is described. This fragment retains the opsonic antibody epitope of the native molecule. The sequence of PepM49, as determined by automated Edman degradations of the uncleaved molecule, and its tryptic and chymotryptic peptides, consists of a total of 143 residues (Mr = 17,187). PepM49, a nephritis-associated M protein serotype, exhibits significant internal homology in its sequence. However, identical sequence repeats of the kind seen in the rheumatic fever-associated serotypes M5, M6, and M24, are absent in PepM49. PepM49 exhibits varying degrees of homology with the M5, M6, and M24 proteins, which is consistent with the existence of variable and conserved regions in the M protein molecule. Predictive analysis as well as CD measurements revealed a high propensity of the PepM49 molecule to assume an alpha-helical conformation. Furthermore, a heptad periodicity of the nonpolar residues, a characteristic of alpha-helical coiled-coil proteins, extends over the entire length of the PepM49 protein. The differences in the nonpolar residue distribution divide the PepM49 sequence into three distinct domains, similar to those seen earlier in the M5 and M6 proteins. Together, these studies establish a conserved conformational design for the sequentially diverse M protein serotypes. However, the pattern of heptad periodicity in the PepM49 protein is quite distinct from that present in the PepM5 and M6 proteins, suggesting distinct differences in structural features among conformationally similar M protein serotypes. This may have relevance to the pathological differences associated with these M protein serotypes.
Insights
The amino acid sequence of PepM49, a group A streptococcal M protein fragment, reveals conserved structural designs but distinct patterns compared to other M protein types. This structural variation may explain pathological differences.
Area of Science:
- Microbiology
- Structural Biology
- Immunology
Background:
- Group A Streptococcus (GAS) M proteins are antiphagocytic virulence factors.
- M proteins are highly diverse serotypes, with some linked to rheumatic fever and others to nephritis.
- Understanding M protein structure is crucial for vaccine development and understanding pathogenesis.
Purpose of the Study:
- To determine the complete amino acid sequence of PepM49, a fragment of the nephritis-associated M protein type 49.
- To analyze the structural features and homology of PepM49 with other M protein serotypes.
- To investigate the potential relationship between M protein structure and associated pathologies.
Main Methods:
- Automated Edman degradation was used to sequence PepM49 and its tryptic/chymotryptic peptides.
- Predictive analysis and Circular Dichroism (CD) measurements were employed to assess conformational properties.
- Sequence homology and heptad periodicity analysis were performed to compare PepM49 with other M proteins.
Main Results:
- The complete amino acid sequence of PepM49 (143 residues) was determined.
- PepM49 exhibits significant internal homology and an alpha-helical coiled-coil conformation with heptad periodicity.
- Unlike rheumatic fever-associated M proteins, PepM49 lacks identical sequence repeats but shows homology, indicating conserved and variable regions.
- Distinct nonpolar residue distribution divides PepM49 into three domains, and its heptad periodicity pattern differs from M5 and M6 proteins.
Conclusions:
- Group A Streptococcus M proteins share a conserved conformational design, primarily an alpha-helical coiled-coil structure.
- Despite conformational similarities, distinct patterns in heptad periodicity among M protein serotypes suggest structural variations.
- These structural differences in M proteins may underlie the varying pathological manifestations, such as nephritis versus rheumatic fever.