Purification of recombinant plasminogen activator inhibitor-1 in the active conformation by refolding from inclusion bodies

Reteplase Fc-fusions produced in N. benthamiana are able to dissolve blood clots ex vivo

Thrombolytic and fibrinolytic therapies are effective treatments to dissolve blood clots in stroke therapy. Thrombolytic drugs activate plasminogen to its cleaved form plasmin, a proteolytic enzyme that breaks the crosslinks between fibrin molecules. The FDA-approved human tissue plasminogen activator Reteplase (rPA) is a non-glycosylated protein produced in E. coli. rPA is a deletion mutant of the wild-type Alteplase that benefits from an extended plasma half-life, reduced fibrin specificity and the ability to better penetrate into blood clots. Different methods have been proposed to improve the production of rPA. Here we show for the first time the transient expression in Nicotiana benthamiana of rPA fused to the immunoglobulin fragment crystallizable (Fc) domain on an IgG1, a strategy commonly used to improve the stability of therapeutic proteins. Despite our success on the expression and purification of dimeric rPA-Fc fusions, protein instability results in high amounts of Fc-derived degradation products. We hypothesize that the "Y"- shape of dimeric Fc fusions cause steric hindrance between protein domains and leads to physical instability. Indeed, mutations of critical residues in the Fc dimerization interface allowed the expression of fully stable rPA monomeric Fc-fusions. The ability of rPA-Fc to convert plasminogen into plasmin was demonstrated by plasminogen zymography and clot lysis assay shows that rPA-Fc is able to dissolve blood clots ex vivo. Finally, we addressed concerns with the plant-specific glycosylation by modulating rPA-Fc glycosylation towards serum-like structures including α2,6-sialylated and α1,6-core fucosylated N-glycans completely devoid of plant core fucose and xylose residues.

Plasminogen Activator Inhibitor 1 for Predicting Sepsis Severity and Mortality Outcomes: A Systematic Review and Meta-Analysis

Objectives

Plasminogen activator inhibitor-1 (PAI-1), a crucial regulator of fibrinolysis, is increased in sepsis, but its values in predicting disease severity or mortality outcomes have been controversial. Therefore, we conducted a systematic review and meta-analysis of its predictive values in sepsis.

Methods

PubMed and Embase were searched until August 18, 2017 for studies that evaluated the relationships between PAI-1 levels and disease severity or mortality in sepsis.

Results

A total of 112 and 251 entries were retrieved from the databases, of which 18 studies were included in the final meta-analysis. A total of 4,467 patients (36% male, mean age: 62 years, mean follow-up duration: 36 days) were analyzed. PAI-1 levels were significantly higher in non-survivors than survivors [odds ratios (OR): 3.93, 95% confidence interval (CI): 2.31-6.67, P < 0.0001] and in patients with severe sepsis than in those less severe sepsis (OR: 3.26, 95% CI: 1.37-7.75, P = 0.008).

Conclusion

PAI-1 is a significant predictor of disease severity and all-cause mortality in sepsis. Although the predictive values of PAI-1 reached statistical significance, the clinical utility of PAI-1 in predicting outcomes will require carefully designed prospective trials.

Functional characterization of a new non-Kunitz serine protease inhibitor from the scorpion Lychas mucronatus

Serine protease inhibitors have been widely discovered from different animal venoms, but most of them belong to Kunitz-type toxin subfamily. Here, by screening scorpion venom gland cDNA libraries, we identified four new non-Kunitz serine protease inhibitors with a conserved Ascaris-type structural fold: Ascaris-type toxins Lychas mucronatus Ascaris-type protease inhibitor (LmAPI), Pandinus cavimanus Ascaris-type protease inhibitor (PcAPI), Pandinus cavimanus Ascaris-type protease inhibitor 2 (PcAPI-2), and Hottentotta judaicus Ascaris-type protease inhibitor (HjAPI). The detailed characterization of one Ascaris-type toxin LmAPI was further carried out, which contains 60 residues and possesses a classical Ascaris-type cysteine framework reticulated by five disulfide bridges. Enzyme and inhibitor reaction kinetics experiments showed that recombinant LmAPI inhibits the activity of chymotrypsin potently with a Ki value of 15.5 nM, but has little effect on trypsin and elastase. Bioinformatics analyses suggested that LmAPI contains unique functional residues "TQD" and might be a useful template to produce specific protease inhibitors. Our results indicated that animal venoms are a natural source of new type of protease inhibitors, which will accelerate the development of diagnostic and therapeutic agents for human diseases that target diverse proteases.

SjAPI, the first functionally characterized Ascaris-type protease inhibitor from animal venoms

BACKGROUND

Serine protease inhibitors act as modulators of serine proteases, playing important roles in protecting animal toxin peptides from degradation. However, all known serine protease inhibitors discovered thus far from animal venom belong to the Kunitz-type subfamily, and whether there are other novel types of protease inhibitors in animal venom remains unclear.

PRINCIPAL FINDINGS

Here, by screening scorpion venom gland cDNA libraries, we identified the first Ascaris-type animal toxin family, which contains four members: Scorpiops jendeki Ascaris-type protease inhibitor (SjAPI), Scorpiops jendeki Ascaris-type protease inhibitor 2 (SjAPI-2), Chaerilus tricostatus Ascaris-type protease inhibitor (CtAPI), and Buthus martensii Ascaris-type protease inhibitor (BmAPI). The detailed characterization of Ascaris-type peptide SjAPI from the venom gland of scorpion Scorpiops jendeki was carried out. The mature peptide of SjAPI contains 64 residues and possesses a classical Ascaris-type cysteine framework reticulated by five disulfide bridges, different from all known protease inhibitors from venomous animals. Enzyme and inhibitor reaction kinetics experiments showed that recombinant SjAPI was a dual function peptide with α-chymotrypsin- and elastase-inhibiting properties. Recombinant SjAPI inhibited α-chymotrypsin with a Ki of 97.1 nM and elastase with a Ki of 3.7 μM, respectively. Bioinformatics analyses and chimera experiments indicated that SjAPI contained the unique short side chain functional residues "AAV" and might be a useful template to produce new serine protease inhibitors.

CONCLUSIONS/SIGNIFICANCE

To our knowledge, SjAPI is the first functionally characterized animal toxin peptide with an Ascaris-type fold. The structural and functional diversity of animal toxins with protease-inhibiting properties suggested that bioactive peptides from animal venom glands might be a new source of protease inhibitors, which will accelerate the development of diagnostic and therapeutic agents for human diseases that target diverse proteases.

Plasminogen activator inhibitor type 1 regulates microglial motility and phagocytic activity

Background

Plasminogen activator inhibitor type 1 (PAI-1) is the primary inhibitor of urokinase type plasminogen activators (uPA) and tissue type plasminogen activators (tPA), which mediate fibrinolysis. PAI-1 is also involved in the innate immunity by regulating cell migration and phagocytosis. However, little is known about the role of PAI-1 in the central nervous system.

Methods

In this study, we identified PAI-1 in the culture medium of mouse mixed glial cells by liquid chromatography and tandem mass spectrometry. Secretion of PAI-1 from glial cultures was detected by ELISA and western blotting analysis. Cell migration was evaluated by in vitro scratch-wound healing assay or Boyden chamber assay and an in vivo stab wound injury model. Phagocytic activity was measured by uptake of zymosan particles.

Results

The levels of PAI-1 mRNA and protein expression were increased by lipopolysaccharide and interferon-γ stimulation in both microglia and astrocytes. PAI-1 promoted the migration of microglial cells in culture via the low-density lipoprotein receptor-related protein (LRP) 1/Janus kinase (JAK)/signal transducer and activator of transcription (STAT)1 axis. PAI-1 also increased microglial migration in vivo when injected into mouse brain. PAI-1-mediated microglial migration was independent of protease inhibition, because an R346A mutant of PAI-1 with impaired PA inhibitory activity also promoted microglial migration. Moreover, PAI-1 was able to modulate microglial phagocytic activity. PAI-1 inhibited microglial engulfment of zymosan particles in a vitronectin- and Toll-like receptor 2/6-dependent manner.

Conclusion

Our results indicate that glia-derived PAI-1 may regulate microglial migration and phagocytosis in an autocrine or paracrine manner. This may have important implications in the regulation of brain microglial activities in health and disease.

Specific interactions of serpins in their native forms attenuate their conformational transitions

Plasminogen activator inhibitor-1 (PAI-1) belongs to the serine protease inhibitor (serpin) protein superfamily. Serpins are unique in that their native forms are not the most thermodynamically stable conformation; instead, a more stable, latent conformation exists. During the transition to the latent form, the first strand of beta-sheet C (s1C) in the serpin is peeled away from the beta-sheet, and the reactive center loop (RCL) is inserted into beta-sheet A, rendering the serpin inactive. To elucidate the contribution of specific interactions in the metastable native form to the latency transition, we examined the effect of mutations at the s1C of PAI-1, specifically in positions P4' through P10'. Several mutations strengthened the interactions between these residues and the core protein, and slowed the transition of the protein from the metastable native form to the latent form. In particular, anchoring of the strand to the protein's hydrophobic core at the beginning (P4' site) and center of the strand (P8' site) greatly retarded the latency transition. Mutations that weakened the interactions at the s1C region facilitated the conformational conversion of the protein to the latent form. PAI-1's overall structural stability was largely unchanged by the mutations, as evaluated by urea-induced equilibrium unfolding monitored via fluorescence emission. Therefore, the mutations likely exerted their effects by modulating the height of the energy barrier from the native to the latent form. Our results show that interactions found only in the metastable native form of serpins are important structural features that attenuate folding of the proteins into their latent forms.

Overexpression and purification of single zinc finger peptides of human zinc finger protein ZNF191

ZNF191, a new human zinc finger protein, probably relates to some hereditary diseases and cancers. To obtain structural information of zinc finger domain a convenient method for obtaining milligram quantities of each zinc finger peptide of ZNF191 is necessary. Here, we report an Escherichia coli expression system for rapid and high-level expression of zinc finger 3 and zinc finger 4 of ZNF191. The gene of zinc finger 3 or zinc finger 4 was cloned into pET31b vector to allow expression of single zinc finger peptide as a ketosteroid isomerase (KSI) fusion protein. The KSI-single zinc finger fusion protein was overexpressed in the form of inclusion body, which can be purified by washing several times using buffer solutions, and then be cleaved directly by cyanogen bromide to release single zinc finger peptide. The more than 20mg/L yield of single zinc finger peptide was achieved with more than 95% purity by using YM ultrafiltration membranes. Circular dichroism spectra of these two single zinc finger peptides titrated with Zn(2+) ions demonstrate that they have different secondary structures.

Structural factors affecting the choice between latency transition and polymerization in inhibitory serpins

Plasminogen activator inhibitor-1 (PAI-1), a member of the serine protease inhibitor (serpin) protein family, is unique among the serpins in its conformational lability. This lability allows spontaneous conversion of the active form to a more stable, latent conformation under physiological conditions. In other serpins, polymerization, rather than latency transition, is induced under pathological conditions or upon heat treatment. To identify specific factors promoting latency conversion in PAI-1, we mutated PAI-1 at various positions and compared the effects with those of equivalent mutations in alpha(1)-antitrypsin, the archetypal serpin. Mutations that improved interactions with the turn between helix F and the third strand of beta-sheet A (thFs3A) or the fifth strand of beta-sheet A (s5A), which are near the site of latency transition-associated insertion of the reactive center loop, retarded latency conversion but did not greatly increase structural stability. Mutations that decreased interactions with s2C facilitated conformational conversion, possibly by releasing the reactive center loop from beta-sheet C. Mutations of Thr93 that filled a hydrophobic surface pocket on s2A dramatically increased structural stability but had a negligible effect on the conformational transition. Our results suggest that the structural features controlling latency transition in PAI-1 are highly localized, whereas the conformational strain of the native forms of other inhibitory serpins is distributed throughout the molecule and induces polymerization.

Purification and characterization of a fibrinolytic subtilisin-like protease of Bacillus subtilis TP-6 from an Indonesian fermented soybean, Tempeh

We have isolated a bacterium (TP-6) from the Indonesian fermented soybean, Tempeh, which produces a strong fibrinolytic protease and was identified as Bacillus subtilis. The protease (TPase) was purified to homogeneity by ammonium sulfate fractionation and octyl sepharose and SP sepharose chromatography. The N-terminal amino acid sequence of the 27.5 kDa enzyme was determined, and the encoding gene was cloned and sequenced. The result demonstrates that TPase is a serine protease of the subtilisin family consisting of 275 amino acid residues in its mature form. Its apparent K (m) and V (max) for the synthetic substrate N-succinyl-Ala-Ala-Pro-Phe-pNA were 259 microM and 145 micromol mg(-1) min(-1), respectively. The fibrinogen degradation pattern generated by TPase as a function of time was similar to that obtained with plasmin. In addition, N-terminal amino acid sequence analysis of the fibrinogen degradation products demonstrated that TPase cleaves Glu (or Asp) near hydrophobic acids as a P1 site in the alpha- and beta-chains of fibrinogen to generate fragments D', E', and D' similar to those generated by plasmin. On plasminogen-rich fibrin plates, TPase did not seem to activate fibrin clot lysis. Moreover, the enzyme converted the active plasminogen activator inhibitor-1 to the latent form.

The length of the reactive center loop modulates the latency transition of plasminogen activator inhibitor-1

Plasminogen activator inhibitor-1 (PAI-1) belongs to the serine protease inhibitor (serpin) protein family, which has a common tertiary structure consisting of three beta-sheets and several alpha-helices. Despite the similarity of its structure with those of other serpins, PAI-1 is unique in its conformational lability, which allows the conversion of the metastable active form to a more stable latent conformation under physiological conditions. For the conformational conversion to occur, the reactive center loop (RCL) of PAI-1 must be mobilized and inserted into the major beta-sheet, A sheet. In an effort to understand how the structural conversion is regulated in this conformationally labile serpin, we modulated the length of the RCL of PAI-1. We show that releasing the constraint on the RCL by extension of the loop facilitates a conformational transition of PAI-1 to a stable state. Biochemical data strongly suggest that the stabilization of the transformed conformation is owing to the insertion of the RCL into A beta-sheet, as in the known latent form. In contrast, reducing the loop length drastically retards the conformational change. The results clearly show that the constraint on the RCL is a factor that regulates the conformational transition of PAI-1.

Protein expression and refolding--a practical guide to getting the most out of inclusion bodies

The release of sequence data, particularly from a number of medically and biotechnologically important genomes, is increasing in an exponential fashion. In light of this, elucidating the structure and function of proteins, particularly in a "high throughput" manner, is an important quest. The production of recombinant proteins however is not always straightforward, with a number of proteins falling prey to low expression problems, a high susceptibility to proteolysis and the often despised production of inclusion bodies. Whilst expression as inclusion bodies can often be advantageous, their solubilization and renaturation is often a time consuming and empirical process. In this review, we aim to outline some of the more common approaches that have been applied to a variety of proteins and address issues associated with their handling.