In vitro refolding of triosephosphate isomerase from L. donovani

Mixture of Macromolecular Crowding Agents Has a Non-additive Effect on the Stability of Proteins

The folding and unfolding of proteins inside a cell take place in the presence of macromolecules of various shapes and sizes. Such crowded conditions can significantly affect folding, stability, and biophysical properties of proteins. Thus, to logically mimic the intracellular environment, the thermodynamic stability of two different proteins (lysozyme and α-lactalbumin) was investigated in the presence of mixtures of three crowding agents (ficoll 70, dextran 70, and dextran 40) at different pH values. These crowders possess different shapes and sizes. It was observed that the stabilizing effect of mixtures of crowders is more than the sum effects of the individual crowder, i.e., the stabilizing effect is non-additive in nature. Moreover, dextran 40 (in the mixture) has been found to exhibit the greatest stabilization when compared with other crowders in the mixture. In other words, the small size of the crowder has been observed to be a dominant factor in stabilization of the proteins. Graphical Abstract.

Comparison of effects of anti-angiogenic agents in the zebrafish efficacy-toxicity model for translational anti-angiogenic drug discovery

Background

Anti-angiogenic therapy in certain cancers has been associated with improved control of tumor growth and metastasis. Development of anti-angiogenic agents has, however, been saddled with higher attrition rate due to suboptimal efficacy, narrow therapeutic windows, or development of organ-specific toxicities. The aim of this study was to evaluate the translational ability of the zebrafish efficacy–toxicity model to stratify anti-angiogenic agents based on efficacy, therapeutic windows, and off-target effects to streamline the compound selection process in anti-angiogenic discovery.

Methods

The embryonic model of zebrafish was employed for studying angiogenesis and toxicity. The zebrafish were treated with anti-angiogenic compounds to evaluate their effects on angiogenesis and zebrafish-toxicity parameters. Angiogenesis was measured by scoring the development of subintestinal vessels. Toxicity was evaluated by calculating the median lethal concentration, the lowest observed effect concentration, and gross morphological changes. Results of efficacy and toxicity were used to predict the therapeutic window.

Results

In alignment with the clinical outcomes, the zebrafish assays demonstrated that vascular endothelial growth factor receptor (VEGFR) inhibitors are the most potent anti-angiogenic agents, followed by multikinase inhibitors and inhibitors of endothelial cell proliferation. The toxicity assays reported cardiac phenotype in zebrafish treated with VEGFR inhibitors and multikinase inhibitors with VEGFR activity suggestive of cardiotoxic potential of these compounds. Several other pathological features were reported for multikinase inhibitors suggestive of off-target effects. The predicted therapeutic window was translational with the clinical trial outcomes of the anti-angiogenic agents. The zebrafish efficacy–toxicity approach could stratify anti-angiogenic agents based on the mechanism of action and delineate chemical structure-driven biological activity of anti-angiogenic compounds.

Conclusion

The zebrafish efficacy–toxicity approach can be used as a predictive model for translational anti-angiogenic drug discovery to streamline compound selection, resulting in safer and efficacious anti-angiogenic agents entering the clinics.

A novel hyaluronidase from brown spider (Loxosceles intermedia) venom (Dietrich's Hyaluronidase): from cloning to functional characterization

Loxoscelism is the designation given to clinical symptoms evoked by Loxosceles spider's bites. Clinical manifestations include skin necrosis with gravitational spreading and systemic disturbs. The venom contains several enzymatic toxins. Herein, we describe the cloning, expression, refolding and biological evaluation of a novel brown spider protein characterized as a hyaluronidase. Employing a venom gland cDNA library, we cloned a hyaluronidase (1200 bp cDNA) that encodes for a signal peptide and a mature protein. Amino acid alignment revealed a structural relationship with members of hyaluronidase family, such as scorpion and snake species. Recombinant hyaluronidase was expressed as N-terminal His-tag fusion protein (∼45 kDa) in inclusion bodies and activity was achieved using refolding. Immunoblot analysis showed that antibodies that recognize the recombinant protein cross-reacted with hyaluronidase from whole venom as well as an anti-venom serum reacted with recombinant protein. Recombinant hyaluronidase was able to degrade purified hyaluronic acid (HA) and chondroitin sulfate (CS), while dermatan sulfate (DS) and heparan sulfate (HS) were not affected. Zymograph experiments resulted in ∼45 kDa lytic zones in hyaluronic acid (HA) and chondroitin sulfate (CS) substrates. Through in vivo experiments of dermonecrosis using rabbit skin, the recombinant hyaluronidase was shown to increase the dermonecrotic effect produced by recombinant dermonecrotic toxin from L. intermedia venom (LiRecDT1). These data support the hypothesis that hyaluronidase is a “spreading factor”. Recombinant hyaluronidase provides a useful tool for biotechnological ends. We propose the name Dietrich's Hyaluronidase for this enzyme, in honor of Professor Carl Peter von Dietrich, who dedicated his life to studying proteoglycans and glycosaminoglycans.

Accidents involving brown spiders (Loxosceles genus) are reported throughout the world. South and Southeast of Brazil are endemic areas for this spider. Loxosceles bites commonly trigger local signs as swelling, erythema, hemorrhage and the hallmark symptom: a dermonecrotic lesion with gravitational spreading. Systemic effects are less common; however, are implicated in more severe cases. Hyaluronidases are referred in several venoms as “spreading factors” due to their enzymatic activity upon extracellular components. This activity facilitates the permeation of other toxins through the victim's body. In fact, a previous study identified the activity of L. intermedia venom upon glycosaminoglycans which are abundant components in the extracellular matrix of many tissues. Disclosing a little more about the role of hyaluronidases within this venom, we investigated the activities of a recombinant hyaluronidase from L. intermedia venom. Dietrich's hyaluronidase, as it was designated, was produced as a recombinant protein. By performing a rabbit skin dermonecrosis assay using Dietrich's Hyaluronidase and a dermonecrotic toxin, we showed that Dietrich's Hyaluronidase increased the dermonecrotic area induced by the dermonecrotic toxin. Our results confirm that hyaluronidases are a “spreading factor” of L. intermedia venom.

Enhanced in vitro refolding of soluble human glucocorticoid-induced TNF receptor-related ligand

The glucocorticoid-induced tumor necrosis factor receptor (GITR) is a member of the tumor necrosis factor receptor superfamily. Attachment of GITR to its ligand (GITRL) regulates diverse biological functions, including cell proliferation, differentiation, and survival. In this study, the extracellular region of human GITRL (hGITRL) was cloned, expressed, and purified. The coding sequence of the extracellular region of hGITRL was isolated from human brain cDNA and inserted in pET20b vector. The hGITRL was expressed in Escherichia coli BL21 (DE3) Star at 37 and 25 °C. The majority of the protein was found in inclusion bodies. We identified three important factors for efficient refolding of hGITRL: a ratio of GSH/GSSG, pH, and addition of polyethylene glycol. The renaturated protein was purified by Ni-NTA chromatography. The overall yield of the expression and refolding was higher than 50 mg/l E. coli culture grown at 37 °C. Size exclusion chromatography showed that hGITRL exists as mixture of various multimeric forms in solution. We tested the association of recombinant hGITRL with THP-1 and U937 cell lines and its activity to promote extracellular signal-regulated protein kinase phosphorylation. The results showed that the recombinant protein was biologically active.

Cloning, overexpression and characterization of Leishmania donovani triosephosphate isomerase

Triosephosphate isomerase (TIM) is a major enzyme in the glycolytic pathway, which catalyzes the interconversion of glyceraldehyde 3-phosphate to dihydroxyacetone phosphate. Here, we report cloning, expression and purification of a catalytically active recombinant TIM of Leishmania donovani (LdTIM). The recombinant LdTIM had a pH optimum in the range of 7.2-9.0, found stable at 25°C for 30 min and K(m) and V(max) for the substrate glyceraldehyde 3-phosphate was 0.328±0.02mM and 10.05mM/min/mg, respectively. The cysteine-reactive agent methylmethane thiosulphonate (MMTS) was used as probe, in order to test its effect on enzyme activity. The MMTS induced 75% enzyme inactivation within 15 min at 250 μM concentration. The biochemical characterization of LdTIM described in this work is the essential step towards deeper understanding of its role in parasite survival. The purification of LdTIM in bioactive form provides important tools for further functional and structural studies.