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Streptococcus pyogenes sclB encodes a putative hypervariable surface protein with a collagen-like repetitive
1Infectious Disease Research Group, Department of Biological Sciences, University of Warwick, Coventry CV4 7AL, UK1.
Abstract:
Streptococcus pyogenes is the causative agent in a wide range of diseases of humans of varying severity. During a study scanning the genome sequence of a serotype M1 invasive isolate SF370 for novel surface proteins, an ORF, designated sclB, was identified. The putative protein encoded by sclB contains both a signal peptide and classic Gram-positive wall-associated sequences. Comparison of the sequences of this ORF with those from a number of unrelated isolates demonstrated that sclB encodes a putative surface protein with a variable N-terminal sequence followed by a variable length tract of collagen-like GXY(n) repeats. A further feature of sclB is the presence of CAAAA repeat tracts immediately downstream of the putative start codon. The number of these pentameric repeats varies from 4 to 15 between strains and variation in repeat number results in the predicted SclB protein being either in or out of frame relative to the start codon. These observations suggest that expression of this protein may be regulated at the translational level as a result of gain or loss of CAAAA repeats. While the function of SclB remains to be elucidated, an sclB-specific transcript was detected by RT-PCR during in vitro culture. Finally, it is shown that a second gene, sclA, potentially encoding a protein with a similar extensive collagen-like structure and variable N-terminal sequence, is present in all isolates of S. pyogenes tested to date. Thus S. pyogenes harbours a novel family of structurally related and surface-exposed proteins of potential importance in the pathogenic process.
Insights
Streptococcus pyogenes possesses novel surface proteins, SclA and SclB, featuring collagen-like repeats. SclB expression may be translationally regulated by variable CAAAA repeats, suggesting a role in pathogenesis.
Area of Science:
- Microbiology
- Molecular Biology
- Genomics
Background:
- Streptococcus pyogenes causes diverse human diseases.
- Novel surface proteins are crucial for understanding S. pyogenes pathogenesis.
- Genomic scanning is a method for identifying new virulence factors.
Purpose of the Study:
- To identify and characterize novel surface proteins in Streptococcus pyogenes.
- To investigate the genetic variability and potential regulation of newly identified genes.
- To explore the presence of a novel protein family in S. pyogenes.
Main Methods:
- Genome sequence scanning of an invasive S. pyogenes isolate (SF370).
- Sequence analysis of the identified ORF (sclB) and comparison across multiple isolates.
- RT-PCR to detect sclB-specific transcripts.
- Analysis of gene sclA presence in various S. pyogenes isolates.
Main Results:
- Identification of sclB, encoding a putative surface protein with collagen-like repeats and a variable N-terminal sequence.
- Discovery of variable CAAAA repeat tracts downstream of the sclB start codon, potentially regulating translation.
- Detection of an sclB-specific transcript.
- Identification of sclA, encoding a similar protein, present in all tested S. pyogenes isolates.
Conclusions:
- Streptococcus pyogenes harbors a novel family of structurally related, surface-exposed proteins (SclA and SclB).
- The SclB protein exhibits potential translational regulation via CAAAA repeat variation.
- These proteins may play a significant role in the pathogenic mechanisms of S. pyogenes.