What precisely is going on?
As I interpret this, the protease Pla enzyme inhibits the body's response to infection by inhibiting the "coagulation and fibrinolytic cascades" which I assume means blood clotting but not sure. So possibly, the leucine substitution enhances the efficacy of the enzyme thereby even further inhibiting the body's response to the infection.The plasminogen activator protease (Pla) of Yersinia pestis is a critical virulence determinant in the progression of both bubonic and pneumonic plague. A member of the omptin family of Gram-negative transmembrane proteases, Pla forms a conserved β-barrel fold in the bacterial outer membrane which permits the interaction of the protease with target substrates for cleavage. In vitro studies have identified numerous mammalian host targets, many of which comprise components of the coagulation and fibrinolytic cascades. Through the cleavage of host plasminogen, α2-antiplasmin, plasminogen activator inhibitor-1 (PAI-1), thrombin-activatable fibrinolysis inhibitor (TAFI), and tissue factor pathway inhibitor (TFPI), Pla is hypothesized to disrupt coagulation pathways that are initiated as a natural host response to infection and inflammation. The clearance of fibrin clots, enhanced by the activities of Pla, may alleviate physical barriers to bacterial dissemination and inhibit the recruitment of immune cells