Bee venom is a rich source of pharmacologically active substances. In this study, we characterized a B. terrestris venom Kunitz-type serine protease inhibitor (Bt-KTI). Bt-KTI consists of two exons encoding 82-amino acids (aa), including a predicted 24-aa signal peptide and a 58-aa mature peptide. Recombinant Bt-KTI was expressed as a 6.5-kDa peptide in baculovirus-infected insect cells. Bt-KTI showed no detectable inhibitory effect on factor Xa, thrombin, or tissue plasminogen activator. In contrast, Bt-KTI strongly inhibited plasmin, indicating that it acts as a plasmin inhibitor. The electrophoretic mobility shift assay showed that Bt-KTI binds to plasmin, indicating the formation of a plasmin-Bt-KTI complex. These results demonstrate that Bt-KTI acts as an antifibrinolytic agent, suggesting a role for Bt-KTI as an anti-bleeding agent.

We cloned venom serine proteases from two bumblebee species, Bombus hypocrita sapporoensis and B. ardens ardens. We compared the predicted mature protein sequences of these serine proteasegenes to those previously reported from other bees. Using B. h. sapporoensis venom serine protease(Bs-VSP), we identify that Bs-VSP acts as a fibrin(ogen)olytic enzyme. Bs-VSP activates prothrombin and directly degrades fibrinogen into fibrin degradation products, as demonstrated for B. ignitus and B. terrestrisvenom serine proteases. Our results further define roles for bumblebee venom serine proteases as fibrin(ogen)olytic enzyme, providing strong evidence that bumblebee venom serine proteases are hemostatically active proteins that are potentially promising therapeutic agents.

We present evidence that the serine protease found in bumblebee (Bombus terrestris) venom exhibits fibrin(ogen)olytic activity. Compared to honeybee (Apis mellifera) venom, bumblebee venom contains a higher content of serine protease, which is one of its major components. Venom serine proteases from bumblebees did not cross-react with antibodies against the honeybee venom serine protease. We provide functional evidence indicating that B. terrestris venom serine protease (Bt-VSP) acts as a fibrin(ogen)olytic enzyme. Bt-VSP activates prothrombin and directly degrades fibrinogen into fibrin degradation products. However, Bt-VSP is not a plasminogen activator, and its fibrinolytic activity is less than that of plasmin. Taken together, our results define roles for Bt-VSP as a prothrombin activator, a thrombin-like protease, and a plasmin-like protease, providing significant support for thepotential use of bumblebee venom serine protease as a clinical agent.

Bee venom contains a variety of protein allergens, including serine proteases. Additionally, bee venom has been used in therapeutic application through immunotherapy for bee venom hypersensitivity and venom therapy as an alternative medicine. Here we present a novel view of the application of bee venom through which bee venom serine protease exhibits fibrin(ogen)olytic activity. Compared to honeybee venom, bumblebee venom contains a larger amount of a serine protease as one of its major components. Immunologically, venom serine proteases from bumblebees did not show cross-reactivity with the honeybee venom serine protease. We provide functional evidence indicating that bumblebee (Bombus terrestris) venom serine protease (Bt-VSP) acts as a fibrin(ogen)olytic enzyme. Bt-VSP activates prothrombin and directly degrades fibrinogen into fibrin degradation products, defining roles for Bt-VSP as a prothrombin activator, a thrombin-like protease, and a plasmin-like protease. However, Bt-VSP did not activate plasminogen and the fibrinolytic activity of Bt-VSP is less than plasmin. These findings offer insight into the allergic reaction sequence of bee venom serine protease and its potential usefulness as a clinical agent in the field of hemostasis and thrombosis.

Glutathione S-transferases (GSTs) are multifunctional enzymes that are mainlyinvolved in the xenobiotic metabolism and protection against oxidative damage. Most studies of GSTs in insects have been focused on their role in detoxifying exogenous compounds in particular insecticides. Here, we show the expression profiles of GSTs of the bumblebee Bombus ignitus in response to oxidative stress. We identified a sigma-class GST from B. ignitus (BiGSTS). The BiGSTSgene consists of 4 exons that encode 201 amino acids. Comparative analysis indicates that the predicted amino acid sequence of BiGSTS shares a high identity with the sigma-class GSTs of hymenopteran insects such as Apis mellifera (70% protein sequence identity) and Solenopsis invicta (59% protein sequence identity). Tissue distribution analyses showed the presence of BiGSTS in all tissues examined, including the fat body, midgut, muscle and epidermis. The oxidative stress responses analyzed by quantitative real-time PCR showed that under H2O2 overload, BiGSTS and BiGSTD (identified in our previous study) were upregulated in all tissues examined, including the fat body and midgut of B. ignitus worker bees. Under uniform conditions of H2O2 overload, the expression profile of GSTs and other antioxidant enzyme genes, such as phospholipid-hydroperoxide glutathione peroxidase (Bi-PHGPx) and peroxiredoxins (BiPrx1 and BiTPx1), showed that other antioxidant enzyme genes are acutely induced at 3 h after H2O2 exposure, whereas BiGSTS and BiGSTD are highly induced at 9 h after H2O2 exposure in the fat body of B. ignitus worker bees. These findings indicate that GSTs and other antioxidant enzyme genes in B. ignitusare differentially expressed in response to oxidative stress. Taken together, our findings indicate that BiGSTS and BiGSTD are oxidative stress-inducible antioxidant enzymes that may play a role in oxidative stress response.

Bee venom contains a variety of peptides and enzymes, including serine proteases. Here we describe the molecular cloning and characterization of a serine protease (Bt-VSP) isolated from the venom of the bumblebee Bombus terrestris. The Bt-VSP gene consists of six exons encoding a 358-amino acid protein. The form of Bt-VSP detected in bee venom was the 34-kDa mature protein, which is created by cleavage of the catalytic domain of Bt-proVSP between Arg111 and Val112. Bt-VSP activates prothrombin and directly degrades fibrinogen into fibrin degradation products, defining roles for Bt-VSP as a prothrombin activator, a thrombin-like protease, and a plasmin-like protease. The finding that Bt-VSP acts as a fibrin(ogen)olytic enzyme is similar to a previous finding that Bi-VSP, a venom serine protease of B. ignitus, exhibits fibrin(ogen)olytic activity. We also compared major venom components in honeybee and bumblebee, and found that bumblebee venom contains a larger amount of serine protease. Furthermore, unlike bumblebee venom, which exhibits fibrin(ogen)olytic activity owing to the presence of a serine protease, it is likely that honeybee venom lacks fibrin(ogen)olytic activity.