Semi- and fully synthetic carbohydrate vaccines against pathogenic bacteria: recent developments.

The importance of vaccine-induced protection was repeatedly demonstrated over the last three decades and emphasized during the recent COVID-19 pandemic as the safest and most effective way of preventing infectious diseases. Vaccines have controlled, and in some cases, eradicated global viral and bacterial infections with high efficiency and at a relatively low cost. Carbohydrates form the capsular sugar coat that surrounds the outer surface of human pathogenic bacteria. Specific surface-exposed bacterial carbohydrates serve as potent vaccine targets that broadened our toolbox against bacterial infections. Since first approved for commercial use, antibacterial carbohydrate-based vaccines mostly rely on inherently complex and heterogenous naturally derived polysaccharides, challenging to obtain in a pure, safe, and cost-effective manner. The introduction of synthetic fragments identical with bacterial capsular polysaccharides provided well-defined and homogenous structures that resolved many challenges of purified polysaccharides. The success of semisynthetic glycoconjugate vaccines against bacterial infections, now in different phases of clinical trials, opened up new possibilities and encouraged further development towards fully synthetic antibacterial vaccine solutions. In this mini-review, we describe the recent achievements in semi- and fully synthetic carbohydrate vaccines against a range of human pathogenic bacteria, focusing on preclinical and clinical studies.

Lectin-Mediated Bacterial Modulation by the Intestinal Nematode Ascaris suum.

Ascariasis is a global health problem for humans and animals. Adult Ascaris nematodes are long-lived in the host intestine where they interact with host cells as well as members of the microbiota resulting in chronic infections. Nematode interactions with host cells and the microbial environment are prominently mediated by parasite-secreted proteins and peptides possessing immunomodulatory and antimicrobial activities. Previously, we discovered the C-type lectin protein AsCTL-42 in the secreted products of adult Ascaris worms. Here we tested recombinant AsCTL-42 for its ability to interact with bacterial and host cells. We found that AsCTL-42 lacks bactericidal activity but neutralized bacterial cells without killing them. Treatment of bacterial cells with AsCTL-42 reduced invasion of intestinal epithelial cells by Salmonella. Furthermore, AsCTL-42 interacted with host myeloid C-type lectin receptors. Thus, AsCTL-42 is a parasite protein involved in the triad relationship between Ascaris, host cells, and the microbiota.

A mutually inhibitory feedback loop between the 20S proteasome and its regulator, NQO1.

NAD(P)H:quinone-oxidoreductase-1 (NQO1) is a cytosolic enzyme that catalyzes the reduction of various quinones using flavin adenine dinucleotide (FAD) as a cofactor. NQO1 has been also shown to rescue proteins containing intrinsically unstructured domains, such as p53 and p73, from degradation by the 20S proteasome through an unknown mechanism. Here, we studied the nature of interaction between NQO1 and the 20S proteasome. Our study revealed a double negative feedback loop between NQO1 and the 20S proteasome, whereby NQO1 prevents the proteolytic activity of the 20S proteasome and the 20S proteasome degrades the apo form of NQO1. Furthermore, we demonstrate, both in vivo and in vitro, that NQO1 levels are highly dependent on FAD concentration. These observations suggest a link between 20S proteolysis and the metabolic cellular state. More generally, the results may represent a regulatory mechanism by which associated cofactors dictate the stability of proteins, thus coordinating protein levels with the metabolic status.

Picking up the pieces: a generic porous Si biosensor for probing the proteolytic products of enzymes.

A multifunctional porous Si biosensor that can both monitor the enzymatic activity of minute samples and allow subsequent retrieval of the entrapped proteolytic products for mass spectrometry analysis is described. The biosensor is constructed by DNA-directed/reversible immobilization of enzymes onto a Fabry-Pérot thin film. We demonstrate high enzymatic activity levels of the immobilized enzymes (more than 80%), while maintaining their specificity. Mild dehybridization conditions allow enzyme recycling and facile surface regeneration for consecutive biosensing analysis. The catalytic activity of the immobilized enzymes is monitored in real time by reflective interferometric Fourier transform spectroscopy. The real-time analysis of minute quantities of enzymes (concentrations at least 1 order of magnitude lower, 0.1 mg mL(-1), in comparison to previous reports, 1 mg mL(-1)), in particular proteases, paves the way for substrate profiling and the identification of cleavage sites. The biosensor configuration is compatible with common proteomic methods and allows for a successful downstream mass spectrometry analysis of the reaction products.

Smaller size packs a stronger punch - Recent advances in small antibody fragments targeting tumour-associated carbohydrate antigens.

Attached to proteins, lipids, or forming long, complex chains, glycans represent the most versatile post-translational modification in nature and surround all human cells. Unique glycan structures are monitored by the immune system and differentiate self from non-self and healthy from malignant cells. Aberrant glycosylations, termed tumour-associated carbohydrate antigens (TACAs), are a hallmark of cancer and are correlated with all aspects of cancer biology. Therefore, TACAs represent attractive targets for monoclonal antibodies for cancer diagnosis and therapy. However, due to the thick and dense glycocalyx as well as the tumour micro-environment, conventional antibodies often suffer from restricted access and limited effectiveness in vivo. To overcome this issue, many small antibody fragments have come forth, showing similar affinity with better efficiency than their full-length counterparts. Here we review small antibody fragments against specific glycans on tumour cells and highlight their advantages over conventional antibodies.

Thiol-Mediated Uptake of a Cysteine-Containing Nanobody for Anticancer Drug Delivery.

The identification of tumor-specific biomarkers is one of the bottlenecks in the development of cancer therapies. Previous work revealed altered surface levels of reduced/oxidized cysteines in many cancers due to overexpression of redox-controlling proteins such as protein disulfide isomerases on the cell surface. Alterations in surface thiols can promote cell adhesion and metastasis, making thiols attractive targets for treatment. Few tools are available to study surface thiols on cancer cells and exploit them for theranostics. Here, we describe a nanobody (CB2) that specifically recognizes B cell lymphoma and breast cancer in a thiol-dependent manner. CB2 binding strictly requires the presence of a nonconserved cysteine in the antigen-binding region and correlates with elevated surface levels of free thiols on B cell lymphoma compared to healthy lymphocytes. Nanobody CB2 can induce complement-dependent cytotoxicity against lymphoma cells when functionalized with synthetic rhamnose trimers. Lymphoma cells internalize CB2 via thiol-mediated endocytosis which can be exploited to deliver cytotoxic agents. CB2 internalization combined with functionalization forms the basis for a wide range of diagnostic and therapeutic applications, rendering thiol-reactive nanobodies promising tools for targeting cancer.

A Penicillium expansum glucose oxidase-encoding gene, GOX2, is essential for gluconic acid production and acidification during colonization of deciduous fruit.

Penicillium expansum, the causal agent of blue mold rot, causes severe postharvest maceration of fruit through secretion of total, d-gluconic acid (GLA). Two P. expansum glucose oxidase (GOX)-encoding genes, GOX1 and GOX2, were analyzed. GOX activity and GLA accumulation were strongly related to GOX2 expression, which increased with pH to a maximum at pH 7.0, whereas GOX1 was expressed at pH 4.0, where no GOX activity or extracellular GLA were detected. This differential expression was also observed at the leading edge of the decaying tissue, where GOX2 expression was dominant. The roles of the GOX genes in pathogenicity were further studied through i) development of P. expansum goxRNAi mutants exhibiting differential downregulation of GOX2, ii) heterologous expression of the P. expansum GOX2 gene in the nondeciduous fruit-pathogen P. chrysogenum, and iii) modulation of GLA production by FeSO(4) chelation. Interestingly, in P. expansum, pH and GLA production elicited opposite effects on germination and biomass accumulation: 26% of spores germinated at pH 7.0 when GOX activity and GLA were highest whereas, in P. chrysogenum at the same pH, when GLA did not accumulate, 72% of spores germinated. Moreover, heterologous expression of P. expansum GOX2 in P. chrysogenum resulted in enhanced GLA production and reduced germination, suggesting negative regulation of spore germination and GLA production. These results demonstrate that pH modulation, mediated by GLA accumulation, is an important factor in generating the initial signal or signals for fungal development leading to host-tissue colonization by P. expansum.

Imaging Keratan Sulfate in Ocular Tissue Sections by Immunofluorescence Microscopy and LA-ICP-MS.

Carbohydrate-specific antibodies can serve as valuable tools to monitor alterations in the extracellular matrix resulting from pathologies. Here, the keratan sulfate-specific monoclonal antibody MZ15 was characterized in more detail by immunofluorescence microscopy as well as laser ablation ICP-MS using tissue cryosections and paraffin-embedded samples. Pretreatment with keratanase II prevented staining of samples and therefore demonstrated efficient enzymatic keratan sulfate degradation. Random fluorescent labeling and site-directed introduction of a metal cage into MZ15 were successful and allowed for a highly sensitive detection of the keratan sulfate landscape in the corneal stroma from rats and human tissue.

Generation of glycan-specific nanobodies.

The development of antibodies that target specific glycan structures on cancer cells or human pathogens poses a significant challenge due to the immense complexity of naturally occurring glycans. Automated glycan assembly enables the production of structurally homogeneous glycans in amounts that are difficult to derive from natural sources. Nanobodies (Nbs) are the smallest antigen-binding domains of heavy-chain-only antibodies (hcAbs) found in camelids. To date, the development of glycan-specific Nbs using synthetic glycans has not been reported. Here, we use defined synthetic glycans for alpaca immunization to elicit glycan-specific hcAbs, and describe the identification, isolation, and production of a Nb specific for the tumor-associated carbohydrate antigen Globo-H. The Nb binds the terminal fucose of Globo-H and recognizes synthetic Globo-H in solution and native Globo-H on breast cancer cells with high specificity. These results demonstrate the potential of our approach for generating glycan-targeting Nbs to be used in biomedical and biotechnological applications.

Sialylated N-glycans mediate monocyte uptake of extracellular vesicles secreted from Plasmodium falciparum-infected red blood cells.

Glycoconjugates on extracellular vesicles (EVs) play a vital role in internalization and mediate interaction as well as regulation of the host immune system by viruses, bacteria, and parasites. During their intraerythrocytic life-cycle stages, malaria parasites, Plasmodium falciparum (Pf) mediate the secretion of EVs by infected red blood cells (RBCs) that carry a diverse range of parasitic and host-derived molecules. These molecules facilitate parasite-parasite and parasite-host interactions to ensure parasite survival. To date, the number of identified Pf genes associated with glycan synthesis and the repertoire of expressed glycoconjugates is relatively low. Moreover, the role of Pf glycans in pathogenesis is mostly unclear and poorly understood. As a result, the expression of glycoconjugates on Pf-derived EVs or their involvement in the parasite life-cycle has yet to be reported. Herein, we show that EVs secreted by Pf-infected RBCs carry significantly higher sialylated complex N-glycans than EVs derived from healthy RBCs. Furthermore, we reveal that EV uptake by host monocytes depends on N-glycoproteins and demonstrate that terminal sialic acid on the N-glycans is essential for uptake by human monocytes. Our results provide the first evidence that Pf exploits host sialylated N-glycans to mediate EV uptake by the human immune system cells.

Unveiling the Sugary Secrets of Plasmodium Parasites.

Plasmodium parasites cause malaria disease, one of the leading global health burdens for humanity, infecting hundreds of millions of people each year. Different glycans on the parasite and the host cell surface play significant roles in both malaria pathogenesis and host defense mechanisms. So far, only small, truncated N- and O-glycans have been identified in Plasmodium species. In contrast, complex glycosylphosphatidylinositol (GPI) glycolipids are highly abundant on the parasite's cell membrane and are essential for its survival. Moreover, the parasites express lectins that bind and exploit the host cell surface glycans for different aspects of the parasite life cycle, such as adherence, invasion, and evasion of the host immune system. In parallel, the host cell glycocalyx and lectin expression serve as the first line of defense against Plasmodium parasites and directly dictate susceptibility to Plasmodium infection. This review provides an overview of the glycobiology involved in Plasmodium-host interactions and its contribution to malaria pathogenesis. Recent findings are presented and evaluated in the context of potential therapeutic exploitation.

Targeting and Inhibiting Plasmodium falciparum Using Ultra-small Gold Nanoparticles.

Malaria, a mosquito-borne disease caused by Plasmodium species, claims more than 400,000 lives globally each year. The increasing drug resistance of the parasite renders the development of new anti-malaria drugs necessary. Alternatively, better delivery systems for already marketed drugs could help to solve the resistance problem. Herein, we report glucose-based ultra-small gold nanoparticles (Glc-NCs) that bind to cysteine-rich domains of Plasmodium falciparum surface proteins. Microscopy shows that Glc-NCs bind specifically to extracellular and all intra-erythrocytic stages of P. falciparum. Glc-NCs may be used as drug delivery agents as illustrated for ciprofloxacin, a poorly soluble antibiotic with low antimalarial activity. Ciprofloxacin conjugated to Glc-NCs is more water-soluble than the free drug and is more potent. Glyco-gold nanoparticles that target cysteine-rich domains on parasites may be helpful for the prevention and treatment of malaria.

Total synthesis of D-glycero-D-mannno-heptose 1ß, 7-bisphosphate with 3-O-amyl amine linker and its monophosphate derivative.

D-Glycero-D-mannno-heptose 1ß, 7-bisphosphate (HBPß) is an important intermediate for constructing the core structure of Gram-negative bacterial lipopolysaccharides and was reported as a pathogen-associated molecular pattern (PAMP) that regulates immune responses. HBPß with 3-O-amyl amine linker and its monophosphate derivative D-glycero-D-mannno-heptose 7-phosphate (HP) with 1α-amyl amine linker have been synthesized as candidates for immunity study of HBPß. The O3-amyl amine linker of heptose was installed by dibutyltin oxide-mediated regioselective alkylation under fine-tuned protecting condition. The stereoselective installation of 1ß-phosphate ester was achieved by NIS-mediated phosphorylation at low temperature. The strategy for installation of 3-O-amyl amine linker onto HBP derivative can be expanded to the syntheses of other conjugation-ready carbohydrates bearing anomeric phosphoester.

Post-translational regulation of p53 function through 20S proteasome-mediated cleavage.

The tumor suppressor p53 is a transcription factor that regulates the expression of a range of target genes in response to cellular stress. Adding to the complexity of understanding its cellular function is that in addition to the full-length protein, several p53 isoforms are produced in humans, harboring diverse expression patterns and functionalities. One isoform, Δ40p53, which lacks the first transactivation domain including the binding region for the negative regulator MDM2, was shown to be a product of alternative translation initiation. Here we report the discovery of an alternative cellular mechanism for Δ40p53 formation. We show that the 20S proteasome specifically cleaves the full-length protein (FLp53) to generate the Δ40p53 isoform. Moreover, we demonstrate that a dimer of FLp53 interacts with a Δ40p53 dimer, creating a functional hetero-tetramer. Consequently, the co-expression of both isoforms attenuates the transcriptional activity of FLp53 in a dominant negative manner. Finally, we demonstrate that following oxidative stress, at the time when the 20S proteasome becomes the major degradation machinery and FLp53 is activated, the formation of Δ40p53 is enhanced, creating a negative feedback loop that balances FLp53 activation. Overall, our results suggest that Δ40p53 can be generated by a 20S proteasome-mediated post-translational mechanism so as to control p53 function. More generally, the discovery of a specific cleavage function for the 20S proteasome may represent a more general cellular regulatory mechanism to produce proteins with distinct functional properties.

The Parkinson's-associated protein DJ-1 regulates the 20S proteasome.

The Parkinson's-associated protein, DJ-1, is a highly conserved homodimer, ubiquitously expressed in cells. Here we demonstrate that DJ-1 is a 20S proteasome regulator. We show that DJ-1 physically binds the 20S proteasome and inhibits its activity, rescuing partially unfolded proteins from degradation. Consequently, DJ-1 stabilizes the cellular levels of 20S proteasome substrates, as we show for α-synuclein and p53. Furthermore, we demonstrate that following oxidative stress, DJ-1 is involved in the Nrf2-dependent oxidative stress response that leads to the upregulation of both the 20S proteasome and its regulator, NQO1. Overall, our results suggest a regulatory circuit in which DJ-1, under conditions of oxidative stress, both upregulates and inhibits the 20S proteasome, providing a rigorous control mechanism at a time when the 20S proteasome becomes the major proteolytic machinery. Such a tight regulation of the 20S proteasome may sustain the balance between the need to rapidly eliminate oxidatively damaged proteins and maintain the abundance of native, intrinsically unstructured proteins, which coordinate regulatory and signalling events.

Regulation of focal adhesion formation by a vinculin-Arp2/3 hybrid complex.

Focal adhesions (FAs) are large multi-protein complexes that act as transmembrane links between the extracellular matrix and the actin cytoskeleton. Recently, FAs were extensively characterized, yet the molecular mechanisms underlying their mechanical and signalling functions remain unresolved. To address this question, we isolated protein complexes containing different FA components, from chicken smooth muscle, and characterized their properties. Here we identified 'hybrid complexes' consisting of the actin-nucleating subunits of Arp2/3 and either vinculin or vinculin and α-actinin. We further show that suppression of p41-ARC, a central component of native Arp2/3, which is absent from the hybrid complexes, increases the levels of the Arp2/3-nucleating core in FA sites and stimulates FA growth and dynamics. In contrast, overexpression of p41-ARC adversely affects FAs. These results support the view that Arp2/3 can form modular 'hybrid complexes' containing an actin-nucleating 'functional core', and 'anchoring domains' (vinculin/p41-ARC) that regulate its subcellular localization.

Thermo-resistant intrinsically disordered proteins are efficient 20S proteasome substrates.

Based on software prediction, intrinsically disordered proteins (IDPs) are widely represented in animal cells where they play important instructive roles. Despite the predictive power of the available software programs we nevertheless need simple experimental tools to validate the predictions. IDPs were reported to be preferentially thermo-resistant and also are susceptible to degradation by the 20S proteasome. Analysis of a set of proteins revealed that thermo-resistant proteins are preferred 20S proteasome substrates. Positive correlations are evident between the percent of protein disorder and the level of thermal stability and 20S proteasomal susceptibility. The data obtained from these two assays do not fully overlap but in combination provide a more reliable experimental IDP definition. The correlation was more significant when the IUPred was used as the IDPs predicting software. We demonstrate in this work a simple experimental strategy to improve IDPs identification.