The role and regulation of the extracellular proteases of Staphylococcus aureus

Abstract

Staphylococcus aureus has several extracellular proteases with proposed roles in virulence. SspA (serine protease), SspB (cysteine protease) and Aur (metalloprotease) have been characterized previously and SspA and SspB were found to be cotranscribed. The coding region for the cysteine protease ScpA has been identified and characterized. It is in a probable bi-cistronic operon with scpA located immediately upstream of a coding region for a 108 aa protein that is a specific inhibitor of ScpA. Using primer extension analysis promoters have been mapped and it was found that s A is the only sigma factor involved in the transcription of scpA, sspABC and aur. The transcription of all the genes occurs maximally at post-exponential phase, being positively regulated by agr (accessory gene regulator) and negatively regulated by sarA (staphylococcal accessory regulator). Although the metalloprotease, Aur, does catalyse activation of the SspA zymogen, it is not the sole agent capable of conducting this process. Site-directed mutagenesis revealed that Aur is not capable of undergoing auto-proteolysis to achieve activation. The cysteine protease, ScpA, appears to reside outside this cascade of activation, as mature ScpA was observed in the aur, sspA and sspB mutant strains. Using a mouse abscess model, it has been shown that insertional inactivation of sspA or sspB results in significant attenuation of virulence, whilst mutations in aur or scpA do not. It is likely the attenuation observed in the sspA strain is due to polarity on the sspB gene.

Staphylococcus aureus-Derived Staphopain B, a Potent Cysteine Protease Activator of Plasma Chemerin

“…The effect of clinical isolates on the generation of active chemerin was compared with the effects of the widely used laboratory strains 8325-4 and COL. As demonstrated in Fig. 6B, chemerin activity was triggered by all three clinical isolates tested, as well as by strain 8325-4, but not by the laboratory strain COL. Strain 8325-4 was the most potent in inducing prochemerin activation, which is consistent with its high-level of proteolytic activity (18). Likewise, the lack of prochemerin activation by the COL strain can be explained by the negligible SspB proteolytic Comparison of cell-activating potential of chemerin cleavage products.…”

“…Although SspB activity at S. aureus-infected sites has yet to be quantified, functional SspB is likely to be present within these lesions. Notably, inactivation of SspB and its processing enzyme, the V8 protease, results in attenuation of S. aureus virulence (18,33). Thus while chemerin processing by SspB may provide a host distress "SOS signal" to initiate pDC and/or macrophagemediated immunologic reactions, it is more likely to be an ongoing contributing factor to the pathological outcome of staphylococcal infections.…”

“…Staphopain A (⌬ScpA), SspB (⌬SspB), SspB and V8 protease (⌬SspB⌬V8), and aureolysin (⌬Aur) deficient strains (18) were obtained from Dr. L. Shaw (Department of Biochemistry and Molecular Biology, University of Georgia, Athens, GA) while the Spl proteases (⌬Spl) mutant (19) was a gift from Dr. K. Bayles (Department of Microbiology, Molecular Biology, and Biochemistry, University of Idaho, Moscow, ID). Collection of clinical isolates of S. aureus sampled from joint, blood, and lesional skin of patients suffering from bone infection, sepsis, or atopic dermatitis were donated by Dr. S. Eick (Institute of Medical Microbiology, University Hospital, Jena, Germany) and Dr. M. Kapinska-Mrowiecka (Zeromski General Hospital, Krakow, Poland).…”

Role of Extracellular Proteases in Biofilm Disruption of Gram Positive Bacteria with Special Emphasis on Staphylococcus aureus Biofilms

“…Due to its ability to elaborate a range of virulence factors S. aureus can establish itself in various tissues and surfaces of the human body. Infections caused by this organism can range from superficial lesions, such as wound infections and abscesses, to the more serious life-threatening conditions such as bacteraemia, endocarditis, meningitis and osteomyelitis [12]. Gene transcription and subsequent expression of virulence factors in Staphylococcus aureus is under strict control of two global regulatory elements, agr (accessory gene regulator) and sarA (Staphylococcal accessory regulator A) [13,14].…”

“…The Aur, ScpA, SspA, and SspB proteases are produced as zymogens or pro-enzymes [12,21] (Figure 2). The Aur and ScpA zymogens undergo auto-proteolytic cleavage outside the cell [12] and SspA and SspB are activated in a subsequent proteolytic cascade which is initiated with cleavage of SspA by Aur which then activates SspB [21]. The secreted extracellular proteases have a broad substrate specificity hence can degrade both "self" and "non-self" proteins.…”