Sialidase substrates for Sialdiase assays - activity, specificity, quantification and inhibition

Biochemical characterization of the strict anaerobic Gram-negative bacteria Tannerella forsythia by infrared micro-spectroscopy

Tannerella forsythia is a fastidious S-layer Gram-negative, strict anaerobic, and highly pleomorphic bacterium associated with periodontal inflammatory processes, bone loss, cardiovascular mortality, systemic sequelae, sepsis, and preterm birth. One of the purposes of this study was to characterize, for the first time, Tannerella forsythia (ATCC 43037) using Fourier transform infrared micro-spectroscopy. The analysis aimed to establish a suitable methodology for obtaining reproducible spectra for the characterization of this microorganism, as well as to assign the vibrational bands using techniques such Fourier self-deconvolution analysis (FSD) and second derivative spectral followed by Gaussian band fitting. The study was carried out in triplicate, yielding a total of 25 spectra per culture and 75 spectra across replicates. This methodology can be applied to the biochemical identification and characterization of Tannerella forsythia.

Structural and functional insights into metal coordination and substrate recognition of Akkermansia muciniphila sialidase Amuc_1547

Sialidases in Akkermansia muciniphila are pivotal for mucin degradation, enabling energy acquisition, modulating gut microbiota balance, and influencing host health. However, their structural and functional mechanisms remain poorly characterized. This study resolved the magnesium-bound crystal structure of Amuc_1547, revealing a six-bladed β-propeller fold linked to a carbohydrate-binding module (CBM)-like β-sandwich domain. Structural characterization ​identified a conserved S-x-D-x-G-x-x-W motif, a unique metal-binding pocket coordinated by residues Glu289, Glu299, and Asp300, and a putative carbohydrate substrate-binding pocket within the CBM-like domain. Enzymatic assays confirmed the functional relevance of these structural elements and demonstrated that both metal ions and glycans significantly enhance enzymatic activity. Molecular docking, dynamics simulations, and enzyme kinetics analysis identified critical residue substitutions involved in sialic acid substrate binding and catalysis: Gln367 replaces an arginine in the classical Arg-triplet, while Gln350 and His349 ​replace the nucleophilic tyrosine. These substitutions collectively mediate substrate binding, nucleophilic attack, and transition state stabilization, distinguishing the catalytic mechanism of Amuc_1547 from other six-bladed β-propeller sialidases. Additionally, comparative analysis of the four A. muciniphila sialidases highlights sequence divergence and domain architecture variations, suggesting niche-specific roles in gut microenvironments. Our work not only deciphers the structural basis of metal-dependent substrate recognition in Amuc_1547 but also advances our understanding of the adaptation of A. muciniphila to gut niches, offering a blueprint for leveraging sialidase-driven mucin metabolism in microbiota-targeted therapies.

Rapid Quantification of Neuraminidase Activity by MALDI-TOF MS via On-Target Labeling of Its Substrate and Product

Neuraminidase (NA) is a kind of glycoside hydrolase enzyme, functioning to remove terminal sialic acid (Sia) from glycans which are located on the cell surface. NA plays an essential role in cell interactions with ligands, microbes, and other cells during physiological and pathological processes. Additionally, NA is a major target for developing anti-influenza drugs and influenza vaccines. Herein, a matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) based method to quantify NA activity is demonstrated for the first time. A reactive matrix 2-hydrazinoquinoline (2-HQ) is used to on-target label the natural substrate (3-sialyllactose, 3'-SL) and its enzymatic product (Sia). The derivatization enhances the ionization efficiency of 3'-SL and Sia, especially in negative ion detection mode. Moreover, the lactose ion signals and noise are significantly suppressed. Consequently, NA activity in influenza vaccines has been successfully quantified by comparing the relative intensity of 2-HQ derivatized Sia and 3'-SL in the absence of an additional internal standard. Moreover, the inhibition efficiencies of NA inhibitors have also been measured. Due to its operating simplicity, high-throughput capacity, and quantification accuracy, the proposed method has potential to be applied for the detection of different kinds of NA activity to reveal the role of NA in immunity, vaccine, and infection processes.

Efficient Enzymatic Glycan Engineering of Extracellular Vesicles Using Nanomaterial-Interfaced Microfluidics

Extracellular vesicles (EVs) present a promising modality for numerous biological and medical applications, including therapeutics. Developing facile methods to engineer EVs is essential to meeting the rapidly expanding demand for various functionalized EVs in these applications. Herein, we developed a technology that integrates enzymatic glycoengineering and microfluidics for effective EV functionalization. This method builds on a 3D nanostructured microfluidic device to streamline a multiple-step EV engineering process, which involves a step of enzymatic reaction to install azido-sialic acid residues to glycans on EVs using a sialyltransferase and an azide-tagged sialyl donor followed by the attachment of various functionalities, such as biotin and fluorescent labels, to the resulting azido-glycans on EVs through a biocompatible click reaction. Compared to traditional EV engineering methods, we show that our technology improves the efficiency of EV glycoengineering while simplifying and expediting the workflow. Furthermore, we demonstrated the applicability of this technology to EVs derived from the cell lines of different cancer types, including A549, PC3, and COLO-1 cells. Overall, this EV engineering technology could provide a potentially useful tool for broad applications.

Detection Strategies for Sialic Acid and Sialoglycoconjugates

Glycoconjugates are a vast class of biomolecules implicated in biological processes important for human health and disease. The structural complexity of glycoconjugates remains a challenge to deciphering their precise biological roles and for their development as biomarkers and therapeutics. Human glycoconjugates on the outside of the cell are modified with sialic (neuraminic) acid residues at their termini. The enzymes that install sialic acids are sialyltransferases (SiaTs), a family of 20 different isoenzymes. The removal and degradation of sialic acids is mediated by neuraminidase (NEU; sialidase) enzymes, of which there are four isoenzymes. In this review, we discuss chemical and biochemical approaches for the detection and analysis of sialoglycoconjugate (SGC) structures and their enzymatic products. The most common methods include affinity probes and synthetic substrates. Fluorogenic and radiolabelled substrates are also important tools for many applications, including screening for enzyme inhibitors. Strategies that give insight into the native substrate-specificity of enzymes that regulate SGCs (SiaT & NEU) are necessary to improve our understanding of the role of sialic acid metabolism in health and disease.

Maintaining sidedness and fluidity in cell membrane coatings supported on nano-particulate and planar surfaces

Supported cell membrane coatings meet many requirements set to bioactive nanocarriers and materials, provided sidedness and fluidity of the natural membrane are maintained upon coating. However, the properties of a support-surface responsible for maintaining correct sidedness and fluidity are unknown. Here, we briefly review the properties of natural membranes and membrane-isolation methods, with focus on the asymmetric distribution of functional groups in natural membranes (sidedness) and the ability of molecules to float across a membrane to form functional domains (fluidity). This review concludes that hydrophilic sugar-residues of glycoproteins in the outer-leaflet of cell membranes direct the more hydrophobic inner-leaflet towards a support-surface to create a correctly-sided membrane coating, regardless of electrostatic double-layer interactions. On positively-charged support-surfaces however, strong, electrostatic double-layer attraction of negatively-charged membranes can impede homogeneous coating. In correctly-sided membrane coatings, fluidity is maintained regardless of whether the surface carries a positive or negative charge. However, membranes are frozen on positively-charged, highly-curved, small nanoparticles and localized nanoscopic structures on a support-surface. This leaves an unsupported membrane coating in between nanostructures on planar support-surfaces that is in dual-sided contact with its aqueous environment, yielding enhanced fluidity in membrane coatings on nanostructured, planar support-surfaces as compared with smooth ones.

Evaluation of catalytic activity of human and animal origin viral neuraminidase: Current prospect

With the exception of plants, almost all living organisms synthesize neuraminidase/sialidase. It is a one among the crucial proteins that controls how virulent a microorganism is. An essential enzyme in orthomyxoviruses and paramyxoviruses that destroys receptors is neuraminidase. It plays a number of roles throughout the viral life cycle in addition to one that involves the release of progeny virus particles. This protein is an important target for therapeutic interventions and diagnostic assays. Neuraminidase inhibitors effectively prevent the spread of disease and viral infection. Sensitive, quick, and inexpensive high throughput assays are needed to screen for specific neuraminidase inhibitory chemicals. To characterize the neuraminidase catalytic activity, however, the traditional assays are still the most common in laboratories. This review gives a brief overview of these neuraminidase assays and recent, innovative developments, particularly those involving biosensors.

Molecular approaches for spinal cord injury treatment

Injuries to the spinal cord result in permanent disabilities that limit daily life activities. The main reasons for these poor outcomes are the limited regenerative capacity of central neurons and the inhibitory milieu that is established upon traumatic injuries. Despite decades of research, there is still no efficient treatment for spinal cord injury. Many strategies are tested in preclinical studies that focus on ameliorating the functional outcomes after spinal cord injury. Among these, molecular compounds are currently being used for neurological recovery, with promising results. These molecules target the axon collapsed growth cone, the inhibitory microenvironment, the survival of neurons and glial cells, and the re-establishment of lost connections. In this review we focused on molecules that are being used, either in preclinical or clinical studies, to treat spinal cord injuries, such as drugs, growth and neurotrophic factors, enzymes, and purines. The mechanisms of action of these molecules are discussed, considering traumatic spinal cord injury in rodents and humans.

Ultrasensitive chemiluminescent neuraminidase probe for rapid screening and identification of small-molecules with antiviral activity against influenza A virus in mammalian cells

Influenza A virus is the most virulent influenza subtype and is associated with large-scale global pandemics characterized by high levels of morbidity and mortality. Developing simple and sensitive molecular methods for detecting influenza viruses is critical. Neuraminidase, an exo-glycosidase displayed on the surface of influenza virions, is responsible for the release of the virions and their spread in the infected host. Here, we present a new phenoxy-dioxetane chemiluminescent probe (CLNA) that can directly detect neuraminidase activity. The probe exhibits an effective turn-on response upon reaction with neuraminidase and produces a strong emission signal at 515 nm with an extremely high signal-to-noise ratio. Comparison measurements of our new probe with previously reported analogous neuraminidase optical probes showed superior detection capability in terms of response time and sensitivity. Thus, as far as we know, our probe is the most sensitive neuraminidase probe known to date. The chemiluminescence turn-on response produced by our neuraminidase probe enables rapid screening for small molecules that inhibit viral replication through different mechanisms as validated directly in influenza A-infected mammalian cells using the known inhibitors oseltamivir and amantadine. We expect that our new chemiluminescent neuraminidase probe will prove useful for various applications requiring neuraminidase detection including drug discovery assays against various influenza virus strains in mammalian cells.

A new chemiluminescence neuraminidase probe enables rapid screening of small molecules that inhibit viral replication, directly in influenza A-infected mammalian cells.