Construction, expression and refolding of a bifunctional fusion protein consisting of C-terminal 12-residue of hirudin-PA and reteplase

Heterologous expression, purification and single step efficient refolding of recombinant tissue plasminogen activator (Reteplase) from E. coli

Reteplase (recombinant plasminogen activator, rPA) is a mutant non-glycosylated tissue-type plasminogen activator (tPA) containing 355 amino acids with longer half-life and promising thrombolytic activity than its original counterpart, full length tPA. In this study, we aimed to produce and optimize the purification process of recombinant tissue-type plasminogen activator (tPA) known as Reteplase (rPA). Reteplase cDNA synthesized from total mRNA isolated from human placenta was PCR amplified, cloned into a pET-28a(+) E. coli expression vector and expressed in Rosetta-gami 2 E. coli (NovagenⓇ) host. rPA was expressed as an inclusion body in E. coli and its biological activity was achieved after single step solubilization, purification and refolding. We exploited the strategy of Slow Refolding using Gradual Dialysis (SRGD) in which a refolding buffer containing glutathione oxidized (1 mM GSSG) and glutathione reduced (3 mM GSH) and pH 9.0 was used. Using the SRGD method, we were able to successfully obtain the protein in its active form. We obtained 4.26 mg of active refolded protein from a 50 mL culture that was scaled up in a bioreactor. The purity and homogeneity of rPA was evaluated by SDS-PAGE, Western blotting and mass spectrometry. Circular dichroism spectroscopy was conducted to evaluate the refolding and stability of the refolded rPA in comparison to reference standard rPA. The thrombolytic potential of rPA was assessed by fibrin plate assay and In Vitro clot lysis assay. The presented protocol offers a viable approach for enhancing both the yield and refolding efficiency of reteplase, potentially resulting in an increase in yield.

Insights Into The Effects of Amino Acid Substitutions on The Stability of Reteplase Structure: A Molecular Dynamics Simulation Study

Background

Reteplase (recombinant plasminogen activator, r-PA) is a recombinant protein designed to imitate the endogenous tissue plasminogen activator and catalyze the plasmin production. It is known that the application of reteplase is limited by the complex production processes and protein's stability challenges. Computational redesign of proteins has gained momentum in recent years, particularly as a powerful tool for improving protein stability and consequently its production efficiency. Hence, in the current study, we implemented computational approaches to improve r-PA conformational stability, which fairly correlates with protein's resistance to proteolysis.

Objectives

The current study was developed in order to evaluate the effect of amino acid substitutions on the stability of reteplase structure using molecular dynamic simulations and computational predictions.

Materials and Methods

Several web servers designed for mutation analysis were utilized to select appropriate mutations. Additionally, the experimentally reported mutation, R103S, converting wild type r-PA into non-cleavable form, was also employed. Firstly, mutant collection, consisting of 15 structures, was constructed based on the combinations of four designated mutations. Then, 3D structures were generated using MODELLER. Finally, 17 independent 20-ns molecular dynamics (MD) simulations were conducted and different analysis were performed like root-mean-square deviation (RMSD), root-mean-square fluctuations (RMSF), secondary structure analysis, number of hydrogen bonds, principal components analysis (PCA), eigenvector projection, and density analysis.

Results

Predicted mutations successfully compensated the more flexible conformation caused by R103S substitution, so, improved conformational stability was analyzed from MD simulations. In particular, R103S/A286I/G322I indicated the best results and remarkably enhanced the protein stability.

Conclusion

The conformational stability conferred by these mutations will probably lead to more protection of r-PA in protease-rich environments in various recombinant systems and potentially enhance its production and expression level.

Engineering a "three-in-one" hirudin prodrug to reduce bleeding risk: A proof-of-concept study

An ideal anticoagulant should have at least three properties including targeted delivery to the thrombosis site, local activation or releasing to centralize the anti-thrombosis effects and thus reduce the bleeding risks, and long persistence in circulation to avoid repeated administration. In the present study, we sought to test a "three-in-one" strategy to design new protein anticoagulants. Based on these criteria, we constructed two hirudin prodrugs, R824-HV-ABD and ABD-HV-R824. The R824 peptide can bind phosphatidylserine on the surface of the procoagulant platelets and thus guide the prodrug to the thrombosis sites; albumin-binding domain (ABDs) can bind the prodrug to albumin, and thereby increase its persistence in circulation; the hirudin (HV) core in the prodrug is flanked by factor Xa recognition sites, thus factor Xa at the thrombosis site can cleave the fusion proteins and release the activated hirudin locally. Hirudin prodrugs were able to bind with procoagulant platelets and human serum albumin in vitro with high affinity, targeted concentrated and prevented the formation of occlusive thrombi in rat carotid artery injury model. Their effective time was significantly extended compared to native hirudin, and R824-HV-ABD showed a significantly improved half-life of about 24 h in rats. The bleeding time of prodrug-treated mice was much shorter than that of hirudin-treated mice. The results from the proof-of-concept studies, for the first time, demonstrate that "three-in-one" prodrug strategy may be a good solution for protein or peptide anticoagulants to reduce their bleeding risks.

Pharmacological Activities and Mechanisms of Hirudin and Its Derivatives - A Review

Hirudin, an acidic polypeptide secreted by the salivary glands of Hirudo medicinalis (also known as "Shuizhi" in traditional Chinese medicine), is the strongest natural specific inhibitor of thrombin found so far. Hirudin has been demonstrated to possess potent anti-thrombotic effect in previous studies. Recently, increasing researches have focused on the anti-thrombotic activity of the derivatives of hirudin, mainly because these derivatives have stronger antithrombotic activity and lower bleeding risk. Additionally, various bioactivities of hirudin have been reported as well, including wound repair effect, anti-fibrosis effect, effect on diabetic complications, anti-tumor effect, anti-hyperuricemia effect, effect on cerebral hemorrhage, and others. Therefore, by collecting and summarizing publications from the recent two decades, the pharmacological activities, pharmacokinetics, novel preparations and derivatives, as well as toxicity of hirudin were systematically reviewed in this paper. In addition, the clinical application, the underlying mechanisms of pharmacological effects, the dose-effect relationship, and the development potential in new drug research of hirudin were discussed on the purpose of providing new ideas for application of hirudin in treating related diseases.

Improving long circulation and procoagulant platelet targeting by engineering of hirudin prodrug

To reduce systemic bleeding risks during anticoagulant treatment, a new concept named "precise anticoagulation" was proposed to localize the effects of anticoagulants via the targeted delivery of prodrugs to the coagulation site. In this study, the fusion protein Annexin V-hirudin 3-ABD (hAvHA) was constructed to achieve the prolonged circulation and targeted delivery of hirudin to coagulation sites. hAvHA was inactive as a prodrug, and it could bind to albumin during circulation. The drug was quickly activated via factor Xa-mediated cleavage once coagulation occurred, and hirudin was efficiently released to exert antithrombin activity in vitro. The hAvHA protein could be activated in mouse blood and exert significant anticoagulation effects. The results of FITC labeling illustrated that hAvHA bound to procoagulant platelets, suggesting the Annexin V modification permits targeted delivery to sites of thrombosis. hAvHA bound to albumin in vitro with an equilibrium dissociation constant of 8 pM, suggesting the ABD modification permitted prolonged circulation in vivo. Moreover, the bleeding time was much shorter in hAvHA-treated mice than in hirudin-treated mice. Therefore, our results suggested that that hAvHA is a potential and promising anticoagulant in vivo.

Reteplase: Structure, Function, and Production

Thrombolytic drugs activate plasminogen which creates a cleaved form called plasmin, a proteolytic enzyme that breaks the crosslinks between fibrin molecules. The crosslinks create blood clots, so reteplase dissolves blood clots. Tissue plasminogen activator (tPA) is a well-known thrombolytic drug and is fibrin specific. Reteplase is a modified nonglycosylated recombinant form of tPA used to dissolve intracoronary emboli, lysis of acute pulmonary emboli, and handling of myocardial infarction. This protein contains kringle-2 and serine protease domains. The lack of glycosylation means that a prokaryotic system can be used to express reteplase. Therefore, the production of reteplase is more affordable than that of tPA. Different methods have been proposed to improve the production of reteplase. This article reviews the structure and function of reteplase as well as the methods used to produce it.

Computational design, functional analysis and antigenic epitope estimation of a novel hybrid of 12 peptides of hirudin and reteplase

Cardiovascular and cerebrovascular diseases are leading causes of morbidity and mortality for human beings, and thrombosis is the major risk factor. Thrombolytic therapy has been testified to be the most effective approach to cure thrombosis-related diseases. In clinical treatment, we often adopt a combination therapeutic regimen of both thrombolytic and anticoagulant agents to prevent the recurrence of thrombosis. Thus, a novel hybrid (HV12p-rPA) comprised of the C-terminal 12 residues of hirudin-PA (HV12p) and reteplase (rPA) was designed. The three-dimensional structure of this hybrid was mimicked based on homology modeling and refined with dynamics simulation by utilizing Amber12.0 software. The function of the hybrid was analyzed by structure comparison and the root mean square deviation (RMSD) of Cα atoms between the hybrid and native rPA was calculated. The results showed that HV12p, which was located in the N-terminus of the hybrid, was far from the rPA segment of the hybrid and had no influence on the conformational stability of the rPA domain. The RMSD of Cα atoms of these superimposed proteins was about 40Å, implying that the hybrid had a similar spatial conformation to that of native rPA. Additionally, the antigenic epitopes of the hybrid were predicted by estimations of Hopp-Wood hydrophilicity, Janin accessibility, Zimmermane-Simha polarity, Bhaskaran-Ponnuswamy flexibility, as well as secondary structure analysis and Kolaskar-Tongaonkar antigenicity prediction. The results showed that the most likely antigenic determinants were located at or near regions 148-152, 257-262 and 321-330.