Thrombin-activatable Fibrinolysis Inhibitor Binds to Streptococcus pyogenes by Interacting with Collagen-like Proteins A and B

Abstract

Regulation of proteolysis is a critical element of the host immune system and plays an important role in the induction of pro-and anti-inflammatory reactions in response to infection. Some bacterial species take advantage of these processes and recruit host proteinases to their surface in order to counteract the host attack. Here we show that Thrombin-activatable Fibrinolysis Inhibitor (TAFI), a zinc-dependent procarboxypeptidase, binds to the surface of group A streptococci of an M41 serotype. The interaction is mediated by the streptococcal collagen-like surface proteins A and B (SclA and SclB), and the streptococcal-associated TAFI is then processed at the bacterial surface via plasmin and thrombin-thrombomodulin. These findings suggest an important role for TAFI in the modulation of host responses by streptococci.Streptococcus pyogenes is an important human Gram-positive pathogen that mainly causes throat and skin infections. Although these conditions are normally superficial and selflimiting, they can occasionally turn into invasive and lifethreatening diseases such as sepsis and necrotizing fasciitis (1). In order to colonize the human host, S. pyogenes expresses socalled adhesins, which allow the bacterium to attach to the extracellular matrix or to cell surface structures. So far, at least 20 adhesins have been described in S. pyogenes, including for instance M proteins and protein F1 (for a review see Ref.2). The two related streptococcal collagen-like surface proteins SclA and SclB, which were first described in 2000 and 2001, also belong to this family (3-7). Although their extracellular parts differ in size and primary sequence, SclA and SclB are organized into a similar "lollipop"-like structure. The stalk is made up of a collagen-like region with varying numbers of GXY repeats, whereas the globular head consists of a non-collagenous amino-terminal variable region. Both proteins have a conserved signal peptide and a carboxyl-terminal region that is attached to the cell wall via an LPATG anchor. The collagen-like regions of Scls have been shown to mediate adhesion to human lung epithelial cells (5) and fibroblasts (4). It has also been reported that SclA from M type 41 activates the collagen receptor ␣ 2 ␤ 1 integrin on fibroblasts (8) and interacts with the low density lipoprotein in human plasma (9).Proteolysis plays an important role in host parasite interactions. Although some immune defense mechanisms such as complement, coagulation, and fibrinolysis are dependent on their activation by limited proteolysis, bacteria have evolved strategies to benefit from these host systems by assembling host proteinases at their surface. Probably the best studied interaction in this respect is the binding of plasmin(ogen) to the bacterial surface, which is thought to be a mechanism for the bacteria to trigger their dissemination in the human host (10).Thrombin-activable fibrinolysis inhibitor (TAFI), 2 also known as procarboxypeptidase B, procarboxypeptidase R, and procarboxypeptidase U, is an arginine-and lysi...

Noncollagenous region of the streptococcal collagen‐like protein is a trimerization domain that supports refolding of adjacent homologous and heterologous collagenous domains

“…As the temperature drops below 45 C, the CD signal starts to decrease, suggesting the formation of a-helix and refolding of the V sp domain. When the temperature falls below 25 C, there is a small increase in MRE 220nm , but it never reaches a value expected for formation of a significant amount of triple-helix.…”

“…[21][22][23][24] The Scl1 and Scl2 proteins can bind to thrombin-activatable fibrinolysis inhibitor, which may counteract the host response. 25 Both Scl1 and Scl2 related proteins have been expressed in E. coli, and their conformation, stability, and folding have been studied. [6][7][8] The Scl2 protein from GAS serotype M28 contains a signal peptide, an N-terminal globular domain (denoted as V sp ) of 73 residues, a collagen-like domain (CL sp ) (Gly-Xaa-Yaa) 79 , and a cell wall binding domain which contains an LPXTG motif followed by a hydrophobic transmembrane sequence and a short charged tail.…”

The Crystal Structure of the Streptococcal Collagen-like Protein 2 Globular Domain from Invasive M3-type Group A Streptococcus Shows Significant Similarity to Immunomodulatory HIV Protein gp41

“…Scl1 has also been shown to bind the plasma lipoproteins and complement regulators of the immune system (18,27,28). Furthermore, both Scl1 and Scl2 proteins have been shown to bind thrombinactivatable fibrinolysis inhibitor, interfering with the normal fibrinolytic breakdown of blood clots (26), which may resemble a role of staphylococcal coagulases that produce clots as a protective barrier against the immune response (57). These observations suggest that Scl2 is involved in evasion or modulation of the immune response rather than in host colonization.…”

“…Several biologically relevant V region ligands have been identified using experimental approaches. Thus, different Scl variants bind human extracellular matrix proteins cellular fibronectin and laminin (24) as well as plasma components including the low density lipoprotein, thrombin-activatable fibrinolysis inhibitor, and complement-regulatory proteins factor H and factor H-related protein-1 (18,(25)(26)(27)(28). In addition, the CL domain of Scl can bind directly to host cells through the cellular receptors integrins ␣ 2 ␤ 1 and ␣ 11 ␤ 1 (29 -31).…”

Axillary Abscess Complicated by Venous Thrombosis: Identification ofStreptococcus pyogenesby 16S PCR

“…The following S. pyogenes antigens were used for coating: PAM at 0.5 g/ml, GRAB (protein G-related ␣ 2 M-binding protein) at 0.8 g/ml, IdeS (IgG-degrading enzyme of S. pyogenes) at 1.1 g/ml, SpeB (the secreted streptococcal cysteine proteinase) at 0.5 g/ml, and SclA and SclB (streptococcal collagen-like proteins A and B, respectively, both from serotype M41) at 4 g/ml. Antigens were purified as described previously (2,13,19). Serum samples were diluted 1:500 (PAM, GRAB, IdeS, and SpeB) or 1:50 (SclA and SclB).…”