SmSP2: A serine protease secreted by the blood fluke pathogen Schistosoma mansoni with anti-hemostatic properties

Abstract

BackgroundSerine proteases are important virulence factors for many pathogens. Recently, we discovered a group of trypsin-like serine proteases with domain organization unique to flatworm parasites and containing a thrombospondin type 1 repeat (TSR-1). These proteases are recognized as antigens during host infection and may prove useful as anthelminthic vaccines, however their molecular characteristics are under-studied. Here, we characterize the structural and proteolytic attributes of serine protease 2 (SmSP2) from Schistosoma mansoni, one of the major species responsible for the tropical infectious disease, schistosomiasis.Methodology/Principal findingsSmSP2 comprises three domains: a histidine stretch, TSR-1 and a serine protease domain. The cleavage specificity of recombinant SmSP2 was determined using positional scanning and multiplex combinatorial libraries and the determinants of specificity were identified with 3D homology models, demonstrating a trypsin-like endopeptidase mode of action. SmSP2 displayed restricted proteolysis on protein substrates. It activated tissue plasminogen activator and plasminogen as key components of the fibrinolytic system, and released the vasoregulatory peptide, kinin, from kininogen. SmSP2 was detected in the surface tegument, esophageal glands and reproductive organs of the adult parasite by immunofluorescence microscopy, and in the excretory/secretory products by immunoblotting.Conclusions/SignificanceThe data suggest that SmSP2 is secreted, functions at the host-parasite interface and contributes to the survival of the parasite by manipulating host vasodilatation and fibrinolysis. SmSP2 may be, therefore, a potential target for anti-schistosomal therapy.

Schistosoma mansoniglyceraldehyde-3-phosphate dehydrogenase enhances formation of the blood-clot lysis protein plasmin

“…By recruiting host PLMG and promoting its conversion to plasmin, surface SmGAPDH could help drive the degradation of any blood clots forming around schistosomes in the vasculature thus allowing them unrestricted movement in vivo. This finding adds to our knowledge concerning the ability of schistosomes to control hemostasis: the worms have previously been reported to possess a series of ectoenzymes that likely impact blood clot formation by degrading host prothrombotic signaling molecules as well as key coagulation proteins (Elzoheiry et al, 2018b;Leontovyčet al, 2018;Mebius et al, 2013;Wang et al, 2018Wang et al, , 2017.…”

Modulation of Host Immunity by Helminths: The Expanding Repertoire of Parasite Effector Molecules

“…Conversely, a serine protease-2 (SmSP-2) has been found to activate tissue plasminogen activator and plasminogen, both key components of the fibrinolytic system ( Leontovyč et al., 2018 ). Similar activities have been described for other parasite secretions, such as the cathepsin L peptidases FhCL-1, -2, and -3 from F. hepatica , which degrade fibrinogen and fibrin ( Mebius et al., 2018 ), and a plasminogen-binding alpha-enolase from O. volvulus (OvENO), which may promote proteolysis and degradation of the host extracellular matrix for migration of larvae through host tissues ( Jolodar et al., 2003 ).…”

Immunomodulation and Immune Escape Strategies of Gastrointestinal Helminths and Schistosomes

“…Despite this, blood coagulation is hardly ever observed around schistosomes residing in the host's blood vessels. Several mechanisms of schistosomes to hinder blood clot formation have been proposed and one of them is the production of serine protease SmSP2 (69). It consists of three domains: a serine protease domain, a thrombospondin type 1 repeat (TSR-1) and a histidine stretch.…”

“…Additionally, it splits tPA into its more active double chain form, causing even more increase of plasmin. Furthermore, SmSP2 degrades fibronectin in blood clots and the TSR-1 domain in SmSP2 is capable of controlling cell adhesion, which basically allows interaction with other proteins, binding of glycosaminoglycans and inhibits angiogenesis near the schistosome (69). SmSP2 is therefore another clear example of how various the effects of one produced immunomodulatory factor can be.…”