trans-Sialylation: a strategy used to incorporate sialic acid into oligosaccharides

The Amaryllidaceae alkaloid, montanine, is a potential inhibitor of the Trypanosoma cruzi trans-sialidase enzyme

Trypanosoma cruzi is the parasite that causes the chronic malady known as Chagas disease (CD). Only nifurtimox and benznidazole are currently approved to treat CD in acute and chronic phases. To minimize the danger of disease transmission and as a therapy, new compounds that are safer and more effective are required. It has been demonstrated that Amaryllidaceae plants suppress the growth of T. cruzi - the causative agent of CD. However, little research has been done on their potential protein targets in the parasite. In this study, an in-silico approach was used to investigate the interactions of the Amaryllidaceae alkaloids with trans-sialidase, a confirmed protein target of T. cruzi. The nature and efficiency of the main binding modes of the alkaloids were investigated by molecular docking. Trans-sialidase active site residues were bound by the alkaloids with binding energies varying from -8.9 to -6.9 kcal/mol. From the molecular docking investigation, all the alkaloids had strong interactions with the crucial amino acid residues (Glu230, Tyr342, and Asp59) required for trans-sialidase catalysis. Montanine was the most stable compound throughout the molecular dynamics simulation and had a favorable docking binding energy (-8.9 kcal/mol). The binding free energy (MM-GBSA) of the montanine complex was -14.6 kcal/mol. The pharmacokinetic properties investigated demonstrated that all the evaluated compounds exhibit suitable oral administration requirements. Overall, this in silico study suggests that the Amaryllidaceae alkaloids could potentially act as inhibitors of trans-sialidase.Communicated by Ramaswamy H. Sarma.

Structural and functional characterization of cold-active sialidase isolated from Antarctic fungus Penicillium griseofulvum P29

The fungal strain, Penicillium griseofulvum P29, isolated from a soil sample taken from Terra Nova Bay, Antarctica, was found to be a good producer of sialidase (P29). The present study was focused on the purification and structural characterization of the enzyme. P29 enzyme was purified using a Q-Sepharose column and fast performance liquid chromatography separation on a Mono Q column. The determined molecular mass of the purified enzyme of 40 kDa by SDS-PAGE and 39924.40 Da by matrix desorption/ionization mass spectrometry (MALDI-TOF/MS) analysis correlated well with the calculated mass (39903.75 kDa) from the amino acid sequence of the enzyme. P29 sialidase shows a temperature optimum of 37 °C and low-temperature stability, confirming its cold-active nature. The enzyme is more active towards α(2 → 3) sialyl linkages than those containing α(2 → 6) linkages. Based on the determined amino acid sequence and 3D structural modeling, a 3D model of P29 sialidase was presented, and the properties of the enzyme were explained. The conformational stability of the enzyme was followed by fluorescence spectroscopy, and the new enzyme was found to be conformationally stable in the neutral pH range of pH 6 to pH 9. In addition, the enzyme was more stable in an alkaline environment than in an acidic environment. The purified cold-active enzyme is the only sialidase produced and characterized from Antarctic fungi to date.

Synthesis of Neuraminidase-Resistant Sialyllactose Mimetics from N-Acyl Mannosamines using Metabolically Engineered Escherichia coli

Herein, we describe the efficient gram-scale synthesis of α2,3- and α2,6-sialyllactose oligosaccharides as well as mimetics from N-acyl mannosamines and lactose in metabolically engineered bacterial cells grown at high cell density. We designed new Escherichia coli strains co-expressing sialic acid synthase and N-acylneuraminate cytidylyltransferase from Campylobacter jejuni together with the α2,3-sialyltransferase from Neisseria meningitidis or the α2,6-sialyltransferase from Photobacterium sp. JT-ISH-224. Using their mannose transporter, these new strains actively internalized N-acetylmannosamine (ManNAc) and its N-propanoyl (N-Prop), N-butanoyl (N-But) and N-phenylacetyl (N-PhAc) analogs and converted them into the corresponding sialylated oligosaccharides, with overall yields between 10 % and 39 % (200-700 mg.L-1 of culture). The three α2,6-sialyllactose analogs showed similar binding affinity for Sambucus nigra SNA-I lectin as for the natural oligosaccharide. They also proved to be stable competitive inhibitors of Vibrio cholerae neuraminidase. These N-acyl sialosides therefore hold promise for the development of anti-adhesion therapy against influenza viral infections.

Molecular Dynamics Simulations Reveal the Conformational Transition of GH33 Sialidases

Sialidases are increasingly used in the production of sialyloligosaccharides, a significant component of human milk oligosaccharides. Elucidating the catalytic mechanism of sialidases is critical for the rational design of better biocatalysts, thereby facilitating the industrial production of sialyloligosaccharides. Through comparative all-atom molecular dynamics simulations, we investigated the structural dynamics of sialidases in Glycoside Hydrolase family 33 (GH33). Interestingly, several sialidases displayed significant conformational transition and formed a new cleft in the simulations. The new cleft was adjacent to the innate active site of the enzyme, which serves to accommodate the glycosyl acceptor. Furthermore, the residues involved in the specific interactions with the substrate were evolutionarily conserved in the whole GH33 family, highlighting their key roles in the catalysis of GH33 sialidases. Our results enriched the catalytic mechanism of GH33 sialidases, with potential implications in the rational design of sialidases.

Growing impact of sialic acid-containing glycans in future drug discovery

In nature, almost all cells are covered with a complex array of glycan chain namely sialic acids or nuraminic acids, a negatively charged nine carbon sugars which is considered for their great therapeutic importance since long back. Owing to its presence at the terminal end of lipid bilayer (commonly known as terminal sugars), the well-defined sialosides or sialoconjugates have served pivotal role on the cell surfaces and thus, the sialic acid-containing glycans can modulate and mediate a number of imperative cellular interactions. Understanding of the sialo-protein interaction and their roles in vertebrates in regard of normal physiology, pathological variance, and evolution has indeed a noteworthy journey in medicine. In this tutorial review, we present a concise overview about the structure, linkages in chemical diversity, biological significance followed by chemical and enzymatic modification/synthesis of sialic acid containing glycans. A more focus is attempted about the recent advances, opportunity, and more over growing impact of sialosides and sialoconjugates in future drug discovery and development.

Recent progress on health effects and biosynthesis of two key sialylated human milk oligosaccharides, 3'-sialyllactose and 6'-sialyllactose

Human milk oligosaccharides (HMOs), the third major solid component in breast milk, are recognized as the first prebiotics for health benefits in infants. Sialylated HMOs are an important type of HMOs, accounting for approximately 13% of total HMOs. 3'-Sialyllactose (3'-SL) and 6'-sialyllactose (6'-SL) are two simplest sialylated HMOs. Both SLs display promising prebiotic effects, especially in promoting the proliferation of bifidobacteria and shaping the gut microbiota. SLs exhibit several health effects, including antiadhesive antimicrobial ability, antiviral activity, prevention of necrotizing enterocolitis, immunomodulatory activity, regulation of intestinal epithelial cell response, promotion of brain development, and cognition improvement. Both SLs have been approved as "Generally Recognized as Safe" by the American Food and Drug Administration and are commercially added to infant formula. The biosynthesis of SLs using enzymatic or microbial approaches has been widely studied. The enzymatic synthesis of SLs can be realized by two types of enzymes, sialidases with trans-sialidase activity and sialyltransferases. Microbial synthesis can be achieved by the multiple recombinant bacteria in one-pot reaction, which express the enzymes involved in SL synthesis pathways separately or in combination, or by metabolically engineered strains in a fermentation process. In this article, the physiological properties of 3'-SL and 6'-SL are summarized in detail and the biosynthesis of these SLs via enzymatic and microbial synthesis is comprehensively reviewed.

Molecular Recognition of Surface Trans-Sialidases in Extracellular Vesicles of the Parasite Trypanosoma cruzi Using Atomic Force Microscopy (AFM)

Trans-sialidases (TS) are important constitutive macromolecules of the secretome present on the surface of Trypanosoma cruzi (T. cruzi) that play a central role as a virulence factor in Chagas disease. These enzymes have been related to infectivity, escape from immune surveillance and pathogenesis exhibited by this protozoan parasite. In this work, atomic force microscopy (AFM)-based single molecule-force spectroscopy is implemented as a suitable technique for the detection and location of functional TS on the surface of extracellular vesicles (EVs) released by tissue-culture cell-derived trypomastigotes (Ex-TcT). For that purpose, AFM cantilevers with functionalized tips bearing the anti-TS monoclonal antibody mAb 39 as a sense biomolecule are engineered using a covalent chemical ligation based on vinyl sulfonate click chemistry; a reliable, simple and efficient methodology for the molecular recognition of TS using the antibody-antigen interaction. Measurements of the breakdown forces between anti-TS mAb 39 antibodies and EVs performed to elucidate adhesion and forces involved in the recognition events demonstrate that EVs isolated from tissue-culture cell-derived trypomastigotes of T. cruzi are enriched in TS. Additionally, a mapping of the TS binding sites with submicrometer-scale resolution is provided. This work represents the first AFM-based molecular recognition study of Ex-TcT using an antibody-tethered AFM probe.