High-level secretion of the four salivary plasminogen activators from the vampire bat Desmodus rotundus by stably transfected baby hamster kidney cells

Comparison of Activity and Safety of DSPAα1 and Its N-Glycosylation Mutants

DSPAα1 is a potent rude thrombolytic protein with high medicative value. DSPAα1 has two natural N-glycan sites (N153Q-S154-S155, N398Q-K399-T400) that may lead to immune responses when administered in vivo. We aimed to study the effect of its N-glycosylation sites on DSPAα1 in vitro and in vivo by mutating these N-glycosylation sites. In this experiment, four single mutants and one double mutant were predicted and expressed in Pichia pastoris. When the N398Q-K399-T400 site was mutated, the fibrinolytic activity of the mutant was reduced by 75%. When the N153Q-S154-S155 sites were inactivated as described above, the plasminogen activating activity of its mutant was reduced by 40%, and fibrin selectivity was significantly reduced by 21-fold. The introduction of N-glycosylation on N184-G185-A186T and K368N-S369-S370 also considerably reduced the activity and fibrin selectivity of DSPAα1. The pH tolerance and thermotolerance of all mutants did not change significantly. In vivo experiments also confirmed that N-glycosylation mutations can reduce the safety of DSPAα1, lead to prolonged bleeding time, non-physiological reduction of coagulation factor (α2-AP, PAI) concentration, and increase the risk of irregular bleeding. This study ultimately demonstrated the effect of N-glycosylation mutations on the activity and safety of DSPAα1.

Identification, purification, and pharmacological activity analysis of Desmodus rotundus salivary plasminogen activator alpha1 (DSPAα1) expressed in transgenic rabbit mammary glands

Desmodus rotundus plasminogen activator alpha 1(DSPAα1) is a thrombolytic protein with advantages, such as a long half-life, high accuracy and specificity for thrombolysis, wide therapeutic window, and no neurotoxicity. To date, DSPAα1 has only been expressed in the Chinese hamster ovary, insect cells, transgenic tobacco plants, and Pichia pastoris. To the best of our knowledge, we are the first to report the expression of DSPAα1 in transgenic rabbit mammary glands, extract the product, and analyze its pharmacology activity. An efficient mammary gland-specific expression vector pCL25/DSPAα1 was transferred to prokaryotic zygotes in rabbits by microinjection to generate six DSPAα1 transgenic rabbits. The recombinant DSPAα1 (rDSPAα1) expression in transgenic rabbit milk was 1.19 ± 0.26 mg/mL. The rDSPAα1 purification protocol included pretreatment, ammonium sulfate precipitation, benzamidine affinity chromatography, cation exchange chromatography, and Cibacron blue affinity chromatography; approximately 98% purity was achieved using gel electrophoresis. According to sequencing results, the primary structure of rDSPAα1 was consistent with the theoretical design sequence, and its molecular weight was consistent with that of the natural protein. N-terminal sequencing results indicated rDSPAα1 to be a mature protein, as the goat signal peptide sequence of the expression vector was no longer detected. The fibrinolytic activity of rDSPAα1 was estimated to be 773,333 IU/mg. Fibrin-agarose plate assay and in vitro rat blood clot degradation assay showed that rDSPAα1 had strong thrombolytic activity. In conclusion, we report recombinant DSPAα1 with high thrombolytic activity expressed in transgenic rabbit mammary glands.

Towards Development of an Anti-Vampire Bat Vaccine for Rabies Management: Inoculation of Vampire Bat Saliva Induces Immune-Mediated Resistance

The common vampire bat (Desmodus rotundus) is a hematophagous species responsible for paralytic rabies and bite damage that affects livestock, humans and wildlife from Mexico to Argentina. Current measures to control vampires, based upon coumarin-derived poisons, are not used extensively due in part to the high cost of application, risks for bats that share roosts with vampires and residual environmental contamination. Observations that vampire bat bites may induce resistance in livestock against vampire bat salivary anticoagulants encourage research into novel vaccine-based alternatives particularly focused upon increasing livestock resistance to vampire salivary components. We evaluated the action of vampire bat saliva-Freund's incomplete adjuvant administered to sheep with anticoagulant responses induced by repeated vampire bites in a control group and examined characteristics of vampire bat salivary secretion. We observed that injections induced a response against vampire bat salivary anticoagulants stronger than by repeated vampire bat bites. Based upon these preliminary findings, we hypothesize the utility of developing a control technique based on induction of an immunologically mediated resistance against vampire bat anticoagulants and rabies virus via dual delivery of appropriate host and pathogen antigens. Fundamental characteristics of host biology favor alternative strategies than simple culling by poisons for practical, economical, and ecologically relevant management of vampire populations within a One Health context.

Optimized gene synthesis, expression and purification of active salivary plasminogen activator alpha2 (DSPAalpha2) of Desmodus rotundus in Pichia pastoris

Vampire bat salivary plasminogen activators (DSPAs) are thrombolytic agents that are under clinical investigation for the treatment of acute ischemic stroke. In this study, the synthetic active salivary plasminogen activator alpha2 (DSPAalpha2) gene optimized for the preferred codons of Pichia pastoris was assembled from 48 oligonucleotides, and cloned into the yeast expression vector pPIC9 with a strong enhancer from human cytomegalovirus (HCMV). This system achieved high expression of an active DSPAalpha2 in P. pastoris yeast GS115. Secreted active DSPAalpha2 recombinant protein was purified from broth supernatant by a simple one-step procedure on Sephadex chromatography and was confirmed by SDS-PAGE and Western blot analysis. ELISA showed that 2.5mg of recombinant protein could be obtained from 100-ml culture broth supernatant. The fibrinolytic activity of the recombinant DSPAalpha2 was 1.28 x 10(5)IU/mg.

Affinity binding of a vampire bat plasminogen activator to SEC resins

DSPAalpha1 is a recombinant form of the vampire bat plasminogen activator which we have produced in mammalian cell culture. During the development of a recovery process for DSPAalpha1 we observed an unexpected binding interaction between this protein and several types of gel filtration chromatography resins. Under typical operating conditions using neutral pH buffers, we found that DSPA flows through the sizing resin and is fractionated, as expected, according to its molecular size. However, DSPA applied under certain acidic conditions (<pH 3) binds tightly to the Sephacryl series of resins. The protein is not released until solvent conditions are changed, specifically the pH is raised above 3. From the results presented we conclude that this unexpected interaction with the gel filtration media is not simply an ion exchange nor a hydrophobic interaction, but rather a more complex, mixed mode "affinity" like binding. Several structural features of the DSPA protein which may be involved in this unique binding have been examined, including binding after inactivation of its active site, chemical deglycosylation, chemical denaturation, or limited proteolysis. The "affinity" interactions persist despite these treatments and lead us to conclude that there may be a unique peptide sequence(s) within the protein which is responsible for the binding interaction to Sephacryl resins.

O-linked L-fucose is present in Desmodus rotundus salivary plasminogen activator

DSPAalpha1 (Desmodus rotundus salivary plasminogen activator), a plasminogen activator from the saliva of the vampire bat Desmodus rotundus, is an effective thrombolytic agent. An unusual type of posttranslational modification, in which L-fucose is O-glycosidically linked to threonine 61 in the epidermal growth factor domain was found for natural DSPAalpha1 and its recombinant form isolated from Chinese hamster ovary cells. In the present study a combination of carbohydrate and amino acid composition analysis, amino acid sequencing, and mass spectrometry revealed that the L-fucose is bound to residues 56-68 of DSPAalpha1. The amino acid sequence of this glycosylation site agreed with the suggested consensus sequence Cys-Xaa-Xaa-Gly-Gly-Ser/Thr-Cys described for other proteins. Anew strategy for the identification of the modified amino acid was established. Direct evidence for the occurrence of fucosyl-threonine was obtained by mass spectrometry after digestion of the glycopeptide with a mixture of peptidases. On the basis of these results, DSPAalpha1 is a suitable model for studying the influence of O-fucosylation on clearance rates, particularly in comparative studies with the identically fucosylated and structurally related tissue plasminogen activator.

Structural features mediating fibrin selectivity of vampire bat plasminogen activators

The distinguishing characteristic of vampire bat (Desmodus rotundus) salivary plasminogen activators (DSPAs) is their strict requirement for fibrin as a cofactor. DSPAs consist of structural modules known from urokinase (u-PA) and tissue-type plasminogen activator (t-PA) such as finger (F), epidermal growth factor (E), kringle (K), and protease (P), combining to four genetically and biochemically distinct isoenzymes, exhibiting the formulas FEKP (DSPA alpha 1 and alpha 2) and EKP and KP (DSPA beta and DSPA gamma). Only DSPA alpha 1 and alpha 2 bind to fibrin. All DSPAs are single-chain molecules, displaying substantial amidolytic activity. In a plasminogen activation assay, all four DSPAs are almost inactive in the absence of fibrin but strongly stimulated by fibrin addition. The catalytic efficiency (kcat/Km) of DSPA alpha 1 increases 10(5)-fold, whereas the corresponding value of t-PA is only 550. The ratio of the bimolecular rate constants of plasminogen activation in the presence of fibrin versus fibrinogen (fibrin selectivity) of DSPA alpha 1, alpha 2, beta, gamma, and t-PA was found to be 13,000, 6500, 250, 90, and 72, respectively. Whereas all DSPAs are therefore more fibrin dependent and fibrin selective than t-PA, the extent depends on the respective presence of the various domains. The introduction of a plasmin-sensitive cleavage site in a position akin to the one in t-PA partially obliterates fibrin cofactor requirement. Fibrin dependence and fibrin selectivity of DSPAs are accordingly mediated by fibrin binding, which involves the F domain, as yet undefined determinants within the K and P domains, and by the absence of a plasmin-sensitive activation site. These findings transcend the current understanding of fibrin-mediated stimulation of plasminogen activation: in addition to fibrin binding, specific protein-protein interactions come into play, which stabilize the enzyme in its active conformation.

Mouse androgen-dependent epididymal glycoprotein CRISP-1 (DE/AEG): isolation, biochemical characterization, and expression in recombinant form

In the rat, the secretory glycoprotein DE/AEG is one of the main constituents of the epididymal fluid. We have recently reported the cloning of the cDNA for the related cysteine-rich secretory protein-1 (CRISP-1) from murine epididymis (Haendler et al., 1993; Endocrinology 133:192-198). The protein has now been isolated from the same organ and its N-terminal amino acid sequence has been determined. CRISP-1 exhibited an isoelectric point of approximately 6.8. High levels of CRISP-1 antigen were detected in the corpus and cauda of the epididymis, vas deferens, seminal vesicle, prostate, and in the salivary gland by immunohistochemistry. A quantitative analysis of the cauda epididymal fluid by sandwich ELISA revealed that CRISP-1 represented approximately 15% of the total protein. For heterologous expression, the CRISP-1 coding sequence was introduced into the pMPSV/CMV vector before transfection of baby hamster kidney (BHK) cells and selection with puromycin and neomycin. Expression in insect cells was achieved by co-transfection of Sf9 cells with a transfer vector and baculovirus DNA. Recombinant CRISP-1 was isolated in quantities sufficient for structural analysis. Ethyl maleimide treatment showed that all 16 cysteines were engaged in disulfide bonds. Proteolytic digestion demonstrated that the six cysteines localized in the N-terminal moiety formed three bonds with each other, suggesting the existence of two discrete domains in the protein.

Comparison of the bleeding potential of vampire bat salivary plasminogen activator versus tissue plasminogen activator in an experimental rabbit model

BACKGROUND

Vampire bat salivary plasminogen activator (Bat-PA) has significantly greater fibrin specificity than any of the fibrinolytic agents currently in clinical use. This study tests the hypothesis that avoiding fibrinogen depletion may protect against the hemorrhage induced by plasminogen activator treatment.

METHODS AND RESULTS

Bat-PA was compared with tissue-type plasminogen activator (TPA) in a randomized, prospective, and blinded study using a rabbit ear puncture model of fibrinolytic bleeding. The two agents were used at equimolar dosages (42 nmol/kg) that yielded similar thrombolytic efficacies in a rabbit femoral artery thrombosis model. Both Bat-PA and TPA prolong primary bleeding to double the baseline values, from between 2.1 and 2.3 minutes to between 4.8 and 5.2 minutes. Rebleeding from hemostatically stable sites during the 3-hour observation period occurred equally often with Bat-PA and TPA, 31% from preinjection sites and 23% to 25% from postinjection sites. The lag time between the time of plasminogen activator injection and the onset of rebleeding was likewise the same for both agents, most occurring at 41 to 57 minutes. However, a greater number of prolonged primary or rebleeding occurrences continued for longer than 10 minutes (63% versus 36%) or longer than 30 minutes (30% versus 10%) after Bat-PA than TPA injection. Animals treated with TPA showed a dramatic decrease in plasma fibrinogen and factor VIII concentrations, but those in the Bat-PA treatment group showed only a slight decrease from control values.

CONCLUSIONS

The results indicate that fibrinolytic bleeding after plasminogen activator infusion into rabbits did not correlate with the intensity of the plasma proteolytic state. If anything, Bat-PA usage was associated with a higher proportion of more protracted fibrinolytic bleeding episodes, despite the relatively mild lytic state in comparison with that induced by TPA.

Production of vampire bat plasminogen activator DSPA alpha 1 in CHO and insect cells

Salivary plasminogen activator from the vampire bat Desmodus rotundus (DSPA alpha 1) is a promising new thrombolytic agent. Continuous growth of a stably transfected, methotrexate amplified, dhfr- CHO cell line yields up to 60 mg l-1 of DSPA alpha 1. Utilizing an engineered baculovirus 10 mg l-1 were produced in batches of Sf9 insect cells. Recombinant DSPA alpha 1 is purified from both sources using a one-step purification protocol. Although differences in glycosylation were detected, enzymatic activity and fibrin cofactor dependency are unaffected when DSPA alpha 1 derived from the two expression systems is compared.