Identification and Characterization of the scl Gene Encoding a Group A Streptococcus Extracellular Protein Virulence Factor with Similarity to Human Collagen

Abstract

Group A Streptococcus (GAS) expresses cell surface proteins that mediate important biological functions such as resistance to phagocytosis, adherence to plasma and extracellular matrix proteins, and degradation of host proteins. An open reading frame encoding a protein of 348 amino acid residues was identified by analysis of the genome sequence available for a serotype M1 strain. The protein has an LPATGE sequence located near the carboxy terminus that matches the consensus sequence (LPXTGX) present in many gram-positive cell wall-anchored molecules. Importantly, the central region of this protein contains 50 contiguous Gly-X-X triplet amino acid motifs characteristic of the structure of human collagen. The structural gene (designated scl for streptococcal collagen-like) was present in all 50 GAS isolates tested, which together express 21 different M protein types and represent the breadth of genomic diversity in the species. DNA sequence analysis of the gene in these 50 isolates found that the number of contiguous Gly-X-X motifs ranged from 14 in serotype M6 isolates to 62 in a serotype M41 organism. M1 and M18 organisms had the identical allele, which indicates very recent horizontal gene transfer. The gene was transcribed abundantly in the logarithmic but not stationary phase of growth, a result consistent with the occurrence of a DNA sequence with substantial homology with a consensus Mga binding site immediately upstream of the scl open reading frame. Two isogenic mutant M1 strains created by nonpolar mutagenesis of the scl structural gene were not attenuated for mouse virulence as assessed by intraperitoneal inoculation. In contrast, the isogenic mutant derivative made from the M1 strain representative of the subclone most frequently causing human infections was significantly less virulent when inoculated subcutaneously into mice. In addition, both isogenic mutant strains had significantly reduced adherence to human A549 epithelial cells grown in culture. These studies identify a new extracellular GAS virulence factor that is widely distributed in the species and participates in adherence to host cells and soft tissue pathology.

Multilocus analysis of extracellular putative virulence proteins made by group A Streptococcus: Population genetics, human serologic response, and gene transcription

“…All of these proteins are expressed on the GAS cell surface. With the exception of the streptococcal collagen-like protein-2, which was described very recently but not yet characterized in pathogenesis studies, all of these GAS proteins are virulence determinants in one or more model systems (13,43,(47)(48)(49). Involvement in pathogenesis was not studied, but two lines of evidence suggest that some of the 12 proteins we characterized participate in host-pathogen interactions, broadly defined.…”

“…More than 50 extracellular proteins with this motif have been described in Gram-positive bacteria, and many of them are virulence factors (38). For example, in GAS this motif is present in M protein, M-like proteins, C5a peptidase, GRAB protein, serum opacity factor, a fibronectin-binding protein, streptococcal protective antigen, and two collagen-like proteins (13,43,(47)(48)(49). All of these proteins are expressed on the GAS cell surface.…”

Toward a Genome-Wide Systems Biology Analysis of Host-Pathogen Interactions in Group A Streptococcus

“…22 Inasmuch as strain SF370 is genetically distinct from the great majority of strains responsible for contemporary infections caused by M1 strains, and is less virulent, we hypothesized that acquisition of novel genetic elements had created an unusually successful clone of serotype M1. 47,48 To test this hypothesis, we sequenced the genome of a strain that is genetically representative of organisms responsible for contemporary episodes of M1 infections. Genome sequencing, DNA-DNA microarray analysis, and high-throughput single nucleotide polymorphism analysis revealed that this clone evolved from an ancestral strain through a complex series of LGT episodes.…”

Evaluation of sclB gene variation in Streptococcus pyogenes (Lancefield group A Streptococcus) and potential for subtyping

“…Amongst the surface-exposed proteins more recently proposed as virulence factors in GAS are the collagen-like proteins Scl1 and Scl2, also known as SclA and SclB (Lukomski et al, 2000(Lukomski et al, , 2001Rasmussen et al, 2000;Whatmore, 2001). Both streptococcal and human collagens form triple helices (Mohs et al, 2007), leading to the hypothesis that streptococcal collagens could be involved in the production of antibodies that cross-react with host collagens and may play a role in streptococcal autoimmune disease (Xu et al, 2002).…”