Studies on cell wall-attached proteins of Streptococcus pyogenes

Abstract: Cell wall-attached proteins (CWPs) are important for the virulence of Gram-positive bacteria, but are also targets for the host immune system. CWPs have a conserved COOH-terminal region, responsible for cell wall-sorting. A pattern based on this conserved region was developed. The pattern identifies genes encoding CWPs, with high sensitivity and specificity, in whole genomes of Gram-positive bacteria. In genomes of five Gram-positive bacterial species, 19 previously unknown putative CWPs were identified. Three novel CWPs were identified and characterised in Streptococcus pyogenes, an important Gram-positive human pathogen. One CWP, GRAB, binds the human proteinase inhibitor alpha2-macroglobulin to the S. pyogenes surface, thus protecting other CWPs from proteolysis. Moreover, two novel CWPs (SclA and SclB) with regions similar to collagen were studied. These CWPs have a hypervariable NH2-terminal region and a more conserved COOH-terminal collagen-like region. The genes encoding GRAB and the Scl proteins are present in almost all S. pyogenes strains, indicating that these CWPs have important functions. The sclA gene is regulated by Mga, a transcriptional activator of many S. pyogenes genes related to virulence. In contrast, expression of SclB is regulated by repeated DNA sequences affecting protein translation. The repeated sequences facilitate genetic variation and mediate phase variation of SclB. In addition, insertion sequences could also contribute to genetic variation. One insertion sequence, IS1562, was identified in a region of the S. pyogenes chromosome encoding virulence factors.