Degradation of fibrinogen and collagen by staphopains, cysteine proteases released from Staphylococcus aureus

Abstract

Staphylococcus aureus is the most frequently isolated pathogen in Gram-positive sepsis often complicated by a blood clotting disorder, and is the leading cause of infective endocarditis induced by bacterial destruction of endocardial tissues. The bacterium secretes cysteine proteases referred to as staphopain A (ScpA) and staphopain B (SspB). To investigate virulence activities of staphopains pertinent to clotting disorders and tissue destruction, we examined their effects on collagen, one of the major tissue components, and on plasma clotting. Both staphopains prolonged the partial thromboplastin time of plasma in a dose-and activitydependent manner, with SspB being threefold more potent than ScpA. Staphopains also prolonged the thrombin time of both plasma and fibrinogen, indicating that these enzymes can cause impaired plasma clotting through fibrinogen degradation. Whereas SspB cleaved the fibrinogen Aa-chain at the C-terminal region very efficiently, ScpA degraded it rather slowly. This explains the superior ability of the former enzyme to impair fibrinogen clottability. Enzymically active staphopains, at concentrations as low as 10 nM, degraded collagen with comparable efficiency. These results show novel virulence activities of staphopains in degrading fibrinogen and collagen, and suggest an involvement of staphopains in the clotting impairment and tissue destruction caused by staphylococcal infection. INTRODUCTIONSepsis is a serious medical condition, in which living bacteria are present in the bloodstream. Shock and disseminated intravascular coagulation (DIC) are common and potentially fatal consequences of sepsis. DIC occurs in as many as 40 % of sepsis patients, often leading to multiple organ failure (Levi & ten Cate, 1999), and is directly linked to a high mortality rate. Clinical studies have shown that Gram-positive micro-organisms are as common as Gram-negative bacteria in causing sepsis (Ahmed et al., 1991;Kieft et al., 1993).Staphylococcus aureus is the most frequently isolated pathogen in Gram-positive sepsis (Ahmed et al., 1991;Bone, 1993). In addition, this bacterium is the leading cause of infective endocarditis in many regions of the world (Fowler et al., 2005). The development of endocarditis increases the mortality rate of patients with bacteraemia (Chang et al., 2003) et al., 2005). These findings suggest that staphopains contribute to S. aureus septic shock, one of the major fatal complications of sepsis.Clotting induction and a subsequent tendency to bleeding are prominent clinical features of DIC, another lethal outcome of sepsis. Staphopains may participate in the onset of the clotting disorder through activation or inactivation of clotting factors in plasma by proteolytic cleavage. However, the ability of staphopains to affect plasma clotting has not been studied. Invasion of S. aureus into the endocardium to cause infective endocarditis requires the degradation of connective tissue including extracellular matrix proteins, and is facilitated by proteases. In this context, staphy...

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Inhibition of Staphylococcus aureus cysteine proteases by human serpin potentially limits staphylococcal virulence

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