Acute coagulopathy is a serious complication of traumatic brain injury (TBI) and is of uncertain etiology because of the complex nature of TBI. However, recent work has shown a correlation between mortality and abnormal hemostasis resulting from early platelet dysfunction. The aim of the current study was to develop and characterize a rodent model of TBI that mimics the human coagulopathic condition so that mechanisms of the early acute coagulopathy in TBI can be more readily assessed. Studies utilizing a highly reproducible constrained blunt-force brain injury in rats demonstrate a strong correlation with important postinjury pathological changes that are observed in human TBI patients, namely, diminished platelet responses to agonists, especially adenosine diphosphate (ADP), and subarachnoid bleeding. Additionally, administration of a direct thrombin inhibitor, preinjury, recovers platelet functionality to ADP stimulation, indicating a direct role for excess thrombin production in TBI-induced early platelet dysfunction.

Dimeric M-proteins (M-Prt) in group A (GAS) are surface-expressed virulence factors implicated in processes that contribute to the pathogenicity of infection. Sequence analyses of various GAS M-Prts have shown that they contain a highly conserved sortase A-dependent cell wall-anchored C terminus, whereas the surface-exposed N terminus is highly variable, a feature used for identification and serotyping of various GAS strains. This variability also allows for strain-specific responses that suppress host defenses. Previous studies have indeed identified the N-terminal M-Prt B-domain as the site interacting with antiphagocytotic human-host fibrinogen (hFg). Herein, we show that hFg strongly interacts with M-Prts containing highly variable B-domains. We further demonstrate that specific GAS clinical isolates display high affinity for the D-domain of hFg, and this interaction allowed for subsequent surface binding of human-host plasminogen (hPg) to the E-domain of hFg. This GAS surface-bound hPg is then activated by GAS-secreted streptokinase, leading to the generation of an invasive proteolytic bacterial surface. Our results underscore the importance of the human fibrinolytic system in host-pathogen interactions in invasive GAS infections.

Background:The angiogenesis inhibitor, angiostatin, is an internal fragment of the blood zymogen, plasminogen. Results: A fraction of plasminogen contains a reduced Cys 462 -Cys-541 disulfide bond. Conclusion: Reduced plasminogen is the precursor for angiostatin. Significance: The plasminogen disulfide bonds reduced during angiostatin formation are examples of allosteric disulfides, and their structures help define new allosteric disulfide bond configurations.

Virulent strains of Streptococcus pyogenes (GAS) recruit host single-chain human plasminogen (hPg) to the cell surface - where in the case of Pattern D strains of GAS - hPg binds directly to the cells through a surface receptor, plasminogen-binding group A streptococcal M-protein (PAM).  The coinherited Pattern D GAS-secreted streptokinase (SK2b) then accelerates cleavage of hPg at the R561-V562 peptide bond, resulting in the disulfide-linked two-chain protease, plasmin (hPm).  hPm localizes on the bacterial surface, assisting bacterial dissemination via proteolysis of host defense proteins.  Studies using isolated domains from PAM and hPg revealed that the A-domain of PAM binds to the hPg kringle-2 module (K2hPg), but how this relates to the function of the full-length proteins is unclear.  Herein, we use intact proteins to show that the lysine binding site (LBS) of K2hPg is a major determinant of the activation-resistant T-conformation of hPg.  The binding of PAM to the LBS of K2hPg relaxes the conformation of hPg, leading to a greatly enhanced activation rate of hPg by SK2b.  Domain swapping between hPg and mPg emphasizes the importance of the Pg latent heavy chain (residues 1-561) in PAM binding and shows that while SK2b binds to both hPg and mPg, the activation properties of SK are strictly attributed to the serine protease domain (residues 562-791) of hPg.  Overall, these data show that native hPg is locked in an activation-resistant conformation that is relaxed upon its direct binding to PAM, allowing hPm to form and provide GAS cells with a proteolytic surface.