Labeling of influenza viruses with synthetic fluorescent and biotin-labeled lipids

Lipid-mediated biosynthetic labeling strategy for in vivo dynamic tracing of avian influenza virus infection

Monitoring the infection behavior of avian influenza viruses is crucial for understanding viral pathogenesis and preventing its epidemics among people. A number of viral labeling methods have been utilized for tracking viral infection process, but most of them are laborious or decreasing viral activity. Herein we explored a lipid biosynthetic labeling strategy for dynamical tracking the infection of H5N1 pseudotype virus (H5N1p) in host. Biotinylated lipids (biotinyl Cap-PE) were successfully incorporated into viral envelope when it underwent budding process by taking advantage of host cell-derived lipid metabolism. Biotin-H5N1p virus was effectively in situ-labeled with streptavidin-modified near-infrared quantum dots (NIR SA-QDs) using streptavidin-biotin conjugation with well-preserved virus activities. Dual-labeled imaging obviously shows that H5N1p viruses are primarily taken up in host cells via clathrin-mediated endocytosis. In animal models, Virus-conjugated NIR QDs displayed extraordinary photoluminescence, superior stability, and tissue penetration in lung, allowing us to long-term monitor respiratory viral infection in a noninvasive manner. Importantly, the co-localization of viral hemagglutinin protein and QDs in infected lung further conformed the dynamic infection process of virus in vivo. Hence, this in situ QD-labeling strategy based on cell natural biosynthesis provides a brand-new and reliable tool for noninvasion visualizing viral infection in body in a real-time manner.

Rapid one-step biotinylation of biological and non-biological surfaces

We describe a rapid one-step method to biotinylate virtually any biological or non-biological surface. Contacting a solution of biotin-spacer-lipid constructs with a surface will form a coating within seconds on non-biological surfaces or within minutes on most biological membranes including membrane viruses. The resultant biotinylated surface can then be used to interact with avidinylated conjugates, beads, vesicles, surfaces or cells.

Elucidating virus entry using a tetracysteine-tagged virus

Fluorescent tags constitute an invaluable tool in facilitating a deeper understanding of the mechanistic processes governing virus-host interactions. However, when selecting a fluorescent tag for in vivo imaging of cells, a number of parameters and aspects must be considered. These include whether the tag may affect and interfere with protein conformation or localization, cell toxicity, spectral overlap, photo-stability and background. Cumulatively, these constitute challenges to be overcome. Bluetongue virus (BTV), a member of the Orbivirus genus in the Reoviridae family, is a non-enveloped virus that is comprised of two architecturally complex capsids. The outer capsid, composed of two proteins, VP2 and VP5, together facilitate BTV attachment, entry and the delivery of the transcriptionally active core in the cell cytoplasm. Previously, the significance of the endocytic pathway for BTV entry was reported, although a detailed analysis of the role of each protein during virus trafficking remained elusive due to the unavailability of a tagged virus. Described here is the successful modification, and validation, of a segmented genome belonging to a complex and large capsid virus to introduce tags for fluorescence visualization. The data generated from this approach highlighted the sequential dissociation of VP2 and VP5, driven by decreasing pH during the transition from early to late endosomes, and their retention therein as the virus particles progress along the endocytic pathway. Furthermore, the described tagging technology and methodology may prove transferable and allow for the labeling of other non-enveloped complex viruses.

In Situ Bioorthogonal Metabolic Labeling for Fluorescence Imaging of Virus Infection In Vivo

Optical fluorescence imaging is an important strategy to explore the mechanism of virus-host interaction. However, current fluorescent tag labeling strategies often dampen viral infectivity. The present study explores an in situ fluorescent labeling strategy in order to preserve viral infectivity and precisely monitor viral infection in vivo. In contrast to pre-labeling strategy, mice are first intranasally infected with azide-modified H5N1 pseudotype virus (N₃ -H5N1p), followed by injection of dibenzocyclooctyl (DBCO)-functionalized fluorescence 6 h later. The results show that DBCO dye directly conjugated to N₃ -H5N1p in lung tissues through in vivo bioorthogonal chemistry with high specificity and efficacy. More remarkably, in situ labeling rather than conventional prelabeling strategy effectively preserves viral infectivity and immunogenicity both in vitro and in vivo. Hence, in situ bioorthogonal viral labeling is a promising and reliable strategy for imaging and tracking viral infection in vivo.

Synthetic Mucus Nanobarriers for Identification of Glycan-Dependent Primary Influenza A Infection Inhibitors

Current drugs against the influenza A virus (IAV) act by inhibiting viral neuraminidase (NA) enzymes responsible for the release of budding virions from sialoglycans on infected cells. Here, we describe an approach focused on a search for inhibitors that reinforce the protective functions of mucosal barriers that trap viruses en route to the target cells. We have generated mimetics of sialo-glycoproteins that insert into the viral envelope to provide a well-defined mucus-like environment encapsulating the virus. By introducing this barrier, which the virus must breach using its NA enzymes to infect a host cell, into a screening platform, we have been able to identify compounds that provide significant protection against IAV infection. This approach may facilitate the discovery of potent new IAV prophylactics among compounds with NA activities too weak to emerge from traditional drug screens.

Ultra-Fast Glyco-Coating of Non-Biological Surfaces

The ability to glycosylate surfaces has medical and diagnostic applications, but there is no technology currently recognized as being able to coat any surface without the need for prior chemical modification of the surface. Recently, a family of constructs called function-spacer-lipids (FSL) has been used to glycosylate cells. Because it is known that lipid-based material can adsorb onto surfaces, we explored the potential and performance of cell-labelling FSL constructs to "glycosylate" non-biological surfaces. Using blood group A antigen as an indicator, the performance of a several variations of FSL constructs to modify a large variety of non-biological surfaces was evaluated. It was found the FSL constructs when optimised could in a few seconds glycosylate almost any non-biological surface including metals, glass, plastics, rubbers and other polymers. Although the FSL glycan coating was non-covalent, and therefore temporary, it was sufficiently robust with appropriate selection of spacer and surface that it could capture anti-glycan antibodies, immobilize cells (via antibody), and withstand incubation in serum and extensive buffer washing, making it suitable for diagnostic and research applications.