A Pore Forming Toxin-like Protein Derived from Chinese Red Belly Toad Bombina maxima Triggers the Pyroptosis of Hippomal Neural Cells and Impairs the Cognitive Ability of Mice

Toxin-like proteins and peptides of skin secretions from amphibians play important physiological and pathological roles in amphibians. βγ-CAT is a Chinese red-belly toad-derived pore-forming toxin-like protein complex that consists of aerolysin domain, crystalline domain, and trefoil factor domain and induces various toxic effects via its membrane perforation process, including membrane binding, oligomerization, and endocytosis. Here, we observed the death of mouse hippocampal neuronal cells induced by βγ-CAT at a concentration of 5 nM. Subsequent studies showed that the death of hippocampal neuronal cells was accompanied by the activation of Gasdermin E and caspase-1, suggesting that βγ-CAT induces the pyroptosis of hippocampal neuronal cells. Further molecular mechanism studies revealed that the pyroptosis induced by βγ-CAT is dependent on the oligomerization and endocytosis of βγ-CAT. It is well known that the damage of hippocampal neuronal cells leads to the cognitive attenuation of animals. The impaired cognitive ability of mice was observed after intraperitoneal injection with 10 μg/kg βγ-CAT in a water maze assay. Taken together, these findings reveal a previously unknown toxicological function of a vertebrate-derived pore-forming toxin-like protein in the nerve system, which triggers the pyroptosis of hippocampal neuronal cells, ultimately leading to hippocampal cognitive attenuation.

Targeted delivery of oligonucleotides using multivalent protein-carbohydrate interactions

Cell surface protein-carbohydrate interactions are essential for tissue-specific recognition and endocytosis of viruses, some bacteria and their toxins, and many glycoproteins. Often protein-carbohydrate interactions are multivalent - multiple copies of glycans bind simultaneously to multimeric receptors. Multivalency enhances both affinity and binding specificity, and is of interest for targeted delivery of drugs to specific cell types. The first such example of carbohydrate-mediated drug delivery to reach the clinic is Givosiran, a small interfering ribonucleic acid (siRNA) that is conjugated to a trivalent N-acetylgalactosamine (GalNAc) ligand. This ligand enables efficient uptake of the nucleic acid by the asialoglycoprotein receptor (ASGP-R) on hepatocytes. Synthetic multivalent ligands for ASGP-R were among the first 'cluster glycosides' developed at the birth of multivalent glycoscience around 40 years ago. In this review we trace the history of 'GalNAc targeting' from early academic studies to current pharmaceuticals and consider what other opportunities could follow the success of this delivery technology.

Recombinant protein-based injectable materials for biomedical applications

Injectable nanocarriers and hydrogels have found widespread use in a variety of biomedical applications such as local and sustained biotherapeutic cargo delivery, and as cell-instructive matrices for tissue engineering. Recent advances in the development and application of recombinant protein-based materials as injectable platforms under physiological conditions have made them useful platforms for the development of nanoparticles and tissue engineering matrices, which are reviewed in this work. Protein-engineered biomaterials are highly customizable, and they provide distinctly tunable rheological properties, encapsulation efficiencies, and delivery profiles. In particular, the key advantages of emerging technologies which harness the stimuli-responsive properties of recombinant polypeptide-based materials are highlighted in this review.

Bioorthogonal, Bifunctional Linker for Engineering Synthetic Glycoproteins

Post-translational glycosylation of proteins results in complex mixtures of heterogeneous protein glycoforms. Glycoproteins have many potential applications from fundamental studies of glycobiology to potential therapeutics, but generating homogeneous recombinant glycoproteins using chemical or chemoenzymatic reactions to mimic natural glycoproteins or creating homogeneous synthetic neoglycoproteins is a challenging synthetic task. In this work, we use a site-specific bioorthogonal approach to produce synthetic homogeneous glycoproteins. We develop a bifunctional, bioorthogonal linker that combines oxime ligation and strain-promoted azide-alkyne cycloaddition chemistry to functionalize reducing sugars and glycan derivatives for attachment to proteins. We demonstrate the utility of this minimal length linker by producing neoglycoprotein inhibitors of cholera toxin in which derivatives of the disaccharide lactose and GM1os pentasaccharide are attached to a nonbinding variant of the cholera toxin B-subunit that acts as a size- and valency-matched multivalent scaffold. The resulting neoglycoproteins decorated with GM1 ligands inhibit cholera toxin B-subunit adhesion with a picomolar IC50.

Synthesis of cholera toxin B subunit glycoconjugates using site-specific orthogonal oxime and sortase ligation reactions

The chemoenzymatic synthesis of a series of dual N- and C-terminal-functionalized cholera toxin B subunit (CTB) glycoconjugates is described. Mucin 1 peptides bearing different levels of Tn antigen glycosylation [MUC1(Tn)] were prepared via solid-phase peptide synthesis. Using sortase-mediated ligation, the MUC1(Tn) epitopes were conjugated to the C-terminus of CTB in a well-defined manner allowing for high-density display of the MUC1(Tn) epitopes. This work explores the challenges of using sortase-mediated ligation in combination with glycopeptides and the practical considerations to obtain high levels of conjugation. Furthermore, we describe methods to combine two orthogonal labeling methodologies, oxime- and sortase-mediated ligation, to expand the biochemical toolkit and produce dual N- and C-terminal-labeled conjugates.

One, two, many: Strategies to alter the number of carbohydrate binding sites of lectins

Carbohydrates are more than an energy-storage. They are ubiquitously found on cells and most proteins, where they encode biological information. Lectins bind these carbohydrates and are essential for translating the encoded information into biological functions and processes. Hundreds of lectins are known, and they are found in all domains of life. For half a century, researchers have been preparing variants of lectins in which the binding sites are varied. In this way, the traits of the lectins such as the affinity, avidity and specificity towards their ligands as well as their biological efficacy were changed. These efforts helped to unravel the biological importance of lectins and resulted in improved variants for biotechnological exploitation and potential medical applications. This review gives an overview on the methods for the preparation of artificial lectins and complexes thereof and how reducing or increasing the number of binding sites affects their function.

In-Depth Characterization of a Re-Engineered Cholera Toxin Manufacturing Process Using Growth-Decoupled Production in Escherichia coli

Non-toxic derivatives of the cholera toxin are extensively used in neuroscience, as neuronal tracers to reveal the location of cells in the central nervous system. They are, also, being developed as vaccine components and drug-delivery vehicles. Production of cholera-toxin derivatives is often non-reproducible; the quality and quantity require extensive fine-tuning to produce them in lab-scale settings. In our studies, we seek a resolution to this problem, by expanding the molecular toolbox of the Escherichia coli expression system with suitable production, purification, and offline analytics, to critically assess the quality of a probe or drug delivery, based on a non-toxic derivative of the cholera toxin. We present a re-engineered Cholera Toxin Complex (rCTC), wherein its toxic A1 domain was replaced with Maltose Binding Protein (MBP), as a model for an rCTC-based targeted-delivery vehicle. Here, we were able to improve the rCTC production by 11-fold (168 mg/L vs. 15 mg/L), in comparison to a host/vector combination that has been previously used (BL21(DE3) pTRBAB5-G1S). This 11-fold increase in the rCTC production capability was achieved by (1) substantial vector backbone modifications, (2) using Escherichia coli strains capable of growth-decoupling (V strains), (3) implementing a well-tuned fed-batch production protocol at a 1 L scale, and (4) testing the stability of the purified product. By an in-depth characterization of the production process, we revealed that secretion of rCTC across the E. coli Outer Membrane (OM) is processed by the Type II secretion-system general secretory pathway (gsp-operon) and that cholera toxin B-pentamerization is, likely, the rate-limiting step in complex formation. Upon successful manufacturing, we have validated the biological activity of rCTC, by measuring its binding affinity to its carbohydrate receptor GM1 oligosaccharide (Kd = 40 nM), or binding to Jurkat cells (93 pM) and delivering the cargo (MBP) in a retrograde fashion to the cell.

Luminescent terpyridine appended geminal bisazide and bistriazoles: multinuclear Pt(II) complexes and AIPE-based DNA detection with the naked eye

We report square planar Pt(ii) complexes as luminescent biosensors for DNA detection in solution. The sensing is attributed to the aggregation induced bright red photoluminescence (AIPE) of the complexes in the presence of DNA that can be seen with the naked eye using only a 360 nm light source. Terpyridine appended luminescent geminal bistriazoles (L1-L4, from geminal bisazide A through azide-alkyne 'click' cycloaddition) with versatile chelating sites were explored for metal coordination and reaction with Pt(dmso)2Cl2 yielding tetranuclear and dinuclear complexes of Pt(ii) with different N∩N ligand environments. Thermally stable gem-bisazide and bistriazoles are hardly reported in the literature and this is the first report of terpyridine appended geminal bisazide and bistriazoles.