Decreased Amounts of Cell Wall-Associated Protein A and Fibronectin-Binding Proteins in Staphylococcus aureus sarA Mutants due to Up-Regulation of Extracellular Proteases

Abstract

Data have been presented indicating thatStaphylococcus aureus produces several cell surface proteins which bind specifically to different host extracellular matrix proteins and plasma proteins (12,13,32). For many of the cell surface proteins a role in colonization and virulence has been demonstrated in animal models of infection (17,23,27,33). Two highly homologous fibronectin-binding proteins (FnBPA and FnBPB), encoded by fnbA and fnbB, have been characterized (14, 21, 25, 41) and shown to be involved in adherence to damaged heart valves (23) and to promote internalization of S. aureus by epithelial cells (9). Although S. aureus is primarily considered to be an extracellular pathogen, the intracellular niche could promote long-term colonization and maintenance of chronic infections.Protein A (Spa), which binds immunoglobulin G (IgG) by the Fc segment, is a major surface protein present in virtually all strains of S. aureus (10, 11). Strains of S. aureus with a high content of Spa are more resistant to phagocytosis by human neutrophils in vitro than strains with less Spa (34). Reduced virulence of a spa mutant compared to that of the corresponding wild type was demonstrated in a mouse intraperitoneal infection (31).We have recently shown that transcription of the fnbA and fnbB genes is negatively regulated by agr and by an agr-independent mechanism that restricts fnb mRNA synthesis to the early exponential phase of growth (38). A similar temporal control of fnb transcription was also found in another strain of S. aureus (Newman) (43). However, only fnbA appeared to be regulated by agr in this strain. It was also found that fnbA, but not fnbB, was positively regulated by sarA. As for fnbA and fnbB, transcription of spa is negatively regulated by agr (20). However, unlike for fnbA, transcription of spa is negatively controlled by sarA (3,42).Data from recent studies indicate that both FnBPs and protein A may be degraded by extracellular proteases (3, 26, 42). Four major extracellular proteases are produced by S. aureus (1): staphylococcal serine protease (V8 protease) (SspA), a metalloprotease named aureolysin (Aur), a cysteine protease (Scp) named staphopain (18), and a second cysteine protease (SspB) encoded within the same operon as SspA (2, 36).

Identification of a Novel Maturation Mechanism and Restricted Substrate Specificity for the SspB Cysteine Protease ofStaphylococcus aureus

“…SspA exhibits a potent activity in degrading cell surface fibronectin-binding protein adhesins of S. aureus (7,8), and our present data also support a role for SspB in controlling adhesive functions. The fibronectin-binding protein adhesins of S. aureus bind the N-terminal fragment of fibronectin with high affinity and specificity (29,33).…”

“…This followed a report from our laboratory that the cell surface fibronectin-binding protein adhesin of S. aureus was sensitive to degradation by SspA, and its stability was enhanced by supplementing cultures with ␣ 2 -macroglobulin, a protease inhibitor present in plasma (7). Inactivation of SspA promotes enhanced stability of the cell surface fibronectin-binding protein and protein A adhesins (8), and the metalloprotease aureolysin has also been shown to inactivate cell surface clumping factor ClfB by cleaving at a single site (9). These studies have implicated a role for metalloprotease and serine protease activity in controlling S. aureus adhesion functions.…”

An introduction to staphylococcus aureus, and techniques for identifying and quantifying s. aureus adhesins in relation to adhesion to biomaterials: review

“…White arrows indicate presence of background labelling. proteases, specifically V8 protease (SspA) (Figure 4iii), which is repressed by sarA (Karlsson et al, 2001). sarA can also down-regulate the production of protein A at the transcriptional level by binding to the spa promoter 2001).…”

“…Some of these components are involved in attaching the bacteria to surfaces and are virulence determinants. Finally, over 90% of S. aureus clinical strains have been shown to possess capsular polysaccharides (Karakawa and Vann, 1982;Thakker et al, 1998). Capsule production is reported to decrease phagocytosis in vitro, and to enhance S. aureus virulence in a mouse bacteraemia model (Wilkinson and Holmes, 1979;Thakker et al, 1998), therefore acting as a form of biofilm.…”

An Escherichia coli expression system for glutamyl endopeptidases optimized by complete suppression of autodegradation

“…An S. aureus GluV8-deficient mutant was severely attenuated in virulence in mouse abscess, bacteremia, and wound infection models [2]. S. aureus proteases modulate bacterial adhesive molecules, changing the phenotype from adhesive to invasive, and degrade fibronectin-binding proteins and protein A [2], which are adhesion molecules on the staphylococcal surface [3].…”