Adaptive Flexible Sialylated Nanogels as Highly Potent Influenza A Virus Inhibitors.

Flexible multivalent 3D nanosystems that can deform and adapt onto the virus surface via specific ligand-receptor multivalent interactions can efficiently block virus adhesion onto the cell. We here report on the synthesis of a 250 nm sized flexible sialylated nanogel that adapts onto the influenza A virus (IAV) surface via multivalent binding of its sialic acid (SA) residues with hemagglutinin spike proteins on the virus surface. We could demonstrate that the high flexibility of sialylated nanogel improves IAV inhibition by 400 times as compared to a rigid sialylated nanogel in the hemagglutination inhibition assay. The flexible sialylated nanogel efficiently inhibits the influenza A/X31 (H3N2) infection with IC50 values in low picomolar concentrations and also blocks the virus entry into MDCK-II cells.

Sialyl-LacNAc-PNA⋠DNA Concatamers by Rolling-Circle Amplification as Multivalent Inhibitors of Influenza†A Virus Particles.

The surfaces of influenza A virus (IAV) particles are packed with hundreds of homo-trimeric hemagglutinins (HAs). Monovalent sugars have low affinity for HA, but distance-optimized bivalent sialyl-LacNAc (SLN) conjugates bind it with 103 -fold enhanced potency. Herein, we describe the oligomerization of distance-optimized bivalent binders by branched and linear hybridization on long repetitive DNA templates. The most effective complexes fully inhibited IAVs at a DNA template concentration of 10-9 m. Although a 10-2 m concentration of free trisaccharide ligand is required for full inhibition of the virus, DNA templating enables a 104 -fold reduction in the amount of sugar required. Notably, hybridization-induced rigidification of the DNA templates increased the serospecificity. Cryo-TEM analysis revealed that both spaghetti-type linear forms and cotton-ball-like clusters are able to bridge several adjacent HA molecules on the IAV surface. Programmed self-assembly of ligand-nucleic acid conjugates on long DNA templates might provide generic access to target-specific, high-affinity binders of proteins on globular objects such as cells and viruses.

Synthesis and Characterization of a New Bifunctionalized, Fluorescent, and Amphiphilic Molecule for Recruiting SH-Containing Molecules to Membranes.

This study describes the synthesis and characterization of an amphiphilic construct intended to recruit SH-containing molecules to membranes. The construct consists of 1) an aliphatic chain to enable anchoring within membranes, 2) a maleimide moiety to react with the sulfhydryl group of a soluble (bio)molecule, and 3) a fluorescence moiety to allow the construct to be followed by fluorescence spectroscopy and microscopy. It is shown that the construct can be incorporated into preformed membranes, thus allowing application of the approach with biological membranes. The close proximity between the fluorophore and the maleimide moiety within the construct causes fluorescence quenching. This allows monitoring of the reaction with SH-containing molecules by measurement of increases in fluorescence intensity and lifetime. Notably, the construct distributes into laterally ordered membrane domains of lipid vesicles, which is probably triggered by the length of its membrane anchor. The advantages of the new construct can be employed for several biological, biotechnological, and medicinal applications.

Phosphatidylserine Lateral Organization Influences the Interaction of Influenza Virus Matrix Protein 1 with Lipid Membranes.

Influenza A virus matrix protein 1 (M1) is an essential component involved in the structural stability of the virus and in the budding of new virions from infected cells. A deeper understanding of the molecular basis of virion formation and the budding process is required in order to devise new therapeutic approaches. We performed a detailed investigation of the interaction between M1 and phosphatidylserine (PS) (i.e., its main binding target at the plasma membrane [PM]), as well as the distribution of PS itself, both in model membranes and in living cells. To this end, we used a combination of techniques, including Förster resonance energy transfer (FRET), confocal microscopy imaging, raster image correlation spectroscopy, and number and brightness (N&B) analysis. Our results show that PS can cluster in segregated regions in the plane of the lipid bilayer, both in model bilayers constituted of PS and phosphatidylcholine and in living cells. The viral protein M1 interacts specifically with PS-enriched domains, and such interaction in turn affects its oligomerization process. Furthermore, M1 can stabilize PS domains, as observed in model membranes. For living cells, the presence of PS clusters is suggested by N&B experiments monitoring the clustering of the PS sensor lactadherin. Also, colocalization between M1 and a fluorescent PS probe suggest that, in infected cells, the matrix protein can specifically bind to the regions of PM in which PS is clustered. Taken together, our observations provide novel evidence regarding the role of PS-rich domains in tuning M1-lipid and M1-M1 interactions at the PM of infected cells.IMPORTANCE Influenza virus particles assemble at the plasma membranes (PM) of infected cells. This process is orchestrated by the matrix protein M1, which interacts with membrane lipids while binding to the other proteins and genetic material of the virus. Despite its importance, the initial step in virus assembly (i.e., M1-lipid interaction) is still not well understood. In this work, we show that phosphatidylserine can form lipid domains in physical models of the inner leaflet of the PM. Furthermore, the spatial organization of PS in the plane of the bilayer modulates M1-M1 interactions. Finally, we show that PS domains appear to be present in the PM of living cells and that M1 seems to display a high affinity for them.

Membrane properties of hydroxycholesterols related to the brain cholesterol metabolism.

Compared to cholesterol, hydroxycholesterols contain an additional hydroxy group in the alkyl chain and are able to efficiently cross the brain-blood barrier. Therefore, they are responsible for the sterol transfer between brain and circulation. The current study compares the membrane properties of several hydroxycholesterols with those of cholesterol using 2H NMR spectroscopy, a membrane permeability assay, and fluorescence microscopy experiments. It is shown that hydroxycholesterols do not exert the unique impact on membrane properties characteristic for cholesterol with regard to the influence on lipid chain order, membrane permeability and formation of lateral domains.

Influenza A matrix protein M1 multimerizes upon binding to lipid membranes.

The matrix protein M1 plays a pivotal role in the budding of influenza virus from the plasma membrane (PM) of infected cells. This protein interacts with viral genetic material and envelope proteins while binding to the inner leaflet of the PM. Its oligomerization is therefore closely connected to the assembly of viral components and the formation of new virions. Of interest, the molecular details of M1 interaction with lipids and other viral proteins are far from being understood, and it remains to be determined whether the multimerization of M1 is affected by its binding to the PM and interaction with its components. To clarify the connection between M1 oligomerization and binding to lipid membranes, we applied a combination of several quantitative microscopy approaches. First, we used number and brightness (N&B) microscopy to characterize protein multimerization upon interaction with the PM of living cells. Second, we used controlled biophysical models of the PM (i.e., supported bilayers) to delve into the details of M1-lipid and M1-M1 interactions by employing a combination of raster image correlation spectroscopy (RICS), fluorescence correlation spectroscopy (FCS), and atomic force microscopy (AFM). Our results show that M1 oligomer formation is strongly enhanced by membrane binding and does not necessarily require the presence of other viral proteins. Furthermore, we propose a specific model to explain M1 binding to the lipid bilayer and the formation of multimers.

Evaluation of Multivalent Sialylated Polyglycerols for Resistance Induction in and Broad Antiviral Activity against Influenza A Viruses.

The development of multivalent sialic acid-based inhibitors active against a variety of influenza A virus (IAV) strains has been hampered by high genetic and structural variability of the targeted viral hemagglutinin (HA). Here, we addressed this challenge by employing sialylated polyglycerols (PGs). Efficacy of prototypic PGs was restricted to a narrow spectrum of IAV strains. To understand this restriction, we selected IAV mutants resistant to a prototypic multivalent sialylated PG by serial passaging. Resistance mutations mapped to the receptor binding site of HA, which was accompanied by altered receptor binding profiles of mutant viruses as detected by glycan array analysis. Specifying the inhibitor functionalization to 2,6-α-sialyllactose (SL) and adjusting the linker yielded a rationally designed inhibitor covering an extended spectrum of inhibited IAV strains. These results highlight the importance of integrating virological data with chemical synthesis and structural data for the development of sialylated PGs toward broad anti-influenza compounds.