Synthesis and stability studies of bicyclo[6.1.0]nonyne scaffolds for automated solid-phase oligonucleotide synthesis

Two novel bicyclo[6.1.0]nonyne (BCN) linker derivatives, which can be directly incorporated into oligonucleotide sequences during standard automated solid-phase synthesis, are reported. Stabilities of BCN-carbinol and two BCN-oligonucleotides are evaluated under acidic conditions. In addition, derivatized BCN linkers (non-acidic and acid treated) are evaluated for strain-promoted alkyne-azide cycloaddition (SPAAC).

Development of an Effective Functional Lipid Anchor for Membranes (FLAME) for the Bioorthogonal Modification of the Lipid Bilayer of Mesenchymal Stromal Cells

The glycosylation of cellular membranes is crucial for the survival and communication of cells. As our target is the engineering of the glycocalyx, we designed a functionalized lipid anchor for the introduction into cellular membranes called Functional Lipid Anchor for MEmbranes (FLAME). Since cholesterol incorporates very effectively into membranes, we developed a twice cholesterol-substituted anchor in a total synthesis by applying protecting group chemistry. We labeled the compound with a fluorescent dye, which allows cell visualization. FLAME was successfully incorporated in the membranes of living human mesenchymal stromal cells (hMSC), acting as a temporary, nontoxic marker. The availability of an azido function─a bioorthogonal reacting group within the compound─enables the convenient coupling of alkyne-functionalized molecules, such as fluorophores or saccharides. After the incorporation of FLAME into the plasma membrane of living hMSC, we were able to successfully couple our molecule with an alkyne-tagged fluorophore via click reaction. This suggests that FLAME is useful for the modification of the membrane surface. Coupling FLAME with a galactosamine derivative yielded FLAME-GalNAc, which was incorporated into U2OS cells as well as in giant unilamellar vesicles (GUVs) and cell-derived giant plasma membrane vesicles (GPMVs). With this, we have shown that FLAME-GalNAc is a useful tool for studying the partitioning in the liquid-ordered (Lo) and the liquid-disordered (Ld) phases. The molecular tool can also be used to analyze the diffusion behavior in the model and the cell membranes by fluorescence correlation spectroscopy (FCS).

Principles of glycocalyx engineering with hydrophobic-anchored synthetic mucins

The cellular glycocalyx is involved in diverse biological phenomena in health and disease. Yet, molecular level studies have been challenged by a lack of tools to precisely manipulate this heterogeneous structure. Engineering of the cell surface using insertion of hydrophobic-terminal materials has emerged as a simple and efficient method with great promise for glycocalyx studies. However, there is a dearth of information about how the structure of the material affects membrane insertion efficiency and resulting density, the residence time of the material, or what types of cells can be utilized. Here, we examine a panel of synthetic mucin structures terminated in highly efficient cholesterylamide membrane anchors for their ability to engineer the glycocalyx of five different cell lines. We examined surface density, residence time and half-life, cytotoxicity, and the ability be passed to daughter cells. We report that this method is robust for a variety of polymeric structures, long-lasting, and well-tolerated by a variety of cell lines.

Tunable, biodegradable grafting-from glycopolypeptide bottlebrush polymers

The cellular glycocalyx and extracellular matrix are rich in glycoproteins and proteoglycans that play essential physical and biochemical roles in all life. Synthetic mimics of these natural bottlebrush polymers have wide applications in biomedicine, yet preparation has been challenged by their high grafting and glycosylation densities. Using one-pot dual-catalysis polymerization of glycan-bearing α-amino acid N-carboxyanhydrides, we report grafting-from glycopolypeptide brushes. The materials are chemically and conformationally tunable where backbone and sidechain lengths were precisely altered, grafting density modulated up to 100%, and glycan density and identity tuned by monomer feed ratios. The glycobrushes are composed entirely of sugars and amino acids, are non-toxic to cells, and are degradable by natural proteases. Inspired by native lipid-anchored proteoglycans, cholesterol-modified glycobrushes were displayed on the surface of live human cells. Our materials overcome long-standing challenges in glycobrush polymer synthesis and offer new opportunities to examine glycan presentation and multivalency from chemically defined scaffolds.

Synthetic mimics of glycoproteins and proteoglycans have wide applications in biomedicine, yet preparation has been challenged by their high grafting and glycosylation densities. Here the authors show one-pot dual-catalysis polymerization of glycan-bearing α-amino acid N-carboxyanhydrides to form glycopolypeptide brushes.

Bicyclo[6.1.0]nonyne carboxylic acid for the production of stable molecular probes

Bicyclo[6.1.0]non-4-yn-9-ylmethanol (BCN alcohol) is the most prominent strained-alkyne scaffold in chemical biology. Described herein is the synthesis of an oxidized analogue – BCN acid – whose facile functionalization via amide bond formation yields more stable derivatives than the classically encountered carbamates.

We report a novel strained alkyne, coined BCN acid. This compound participates efficiently in diverse bioorthogonal reactions and allows the facile production of amide probes, which showed superior in vitro stability compared to carbamate analogues.

Synthetic glycoscapes: addressing the structural and functional complexity of the glycocalyx

The glycocalyx is an information-dense network of biomacromolecules extensively modified through glycosylation that populates the cellular boundary. The glycocalyx regulates biological events ranging from cellular protection and adhesion to signalling and differentiation. Owing to the characteristically weak interactions between individual glycans and their protein binding partners, multivalency of glycan presentation is required for the high-avidity interactions needed to trigger cellular responses. As such, biological recognition at the glycocalyx interface is determined by both the structure of glycans that are present as well as their spatial distribution. While genetic and biochemical approaches have proven powerful in controlling glycan composition, modulating the three-dimensional complexity of the cell-surface 'glycoscape' at the sub-micrometre scale remains a considerable challenge in the field. This focused review highlights recent advances in glycocalyx engineering using synthetic nanoscale glycomaterials, which allows for controlled de novo assembly of complexity with precision not accessible with traditional molecular biology tools. We discuss several exciting new studies in the field that demonstrate the power of precision glycocalyx editing in living cells in revealing and controlling the complex mechanisms by which the glycocalyx regulates biological processes.

ABO Blood Group Antigen Decorated Giant Unilamellar Vesicles Exhibit Distinct Interactions with Plasmodium falciparum Infected Red Blood Cells

Severe malaria is considered to be the deadliest disease of this century, primarily among children in sub-Saharan Africa. It stems from infection by the virulent parasite Plasmodium falciparum. The pathogenesis of the disease is based on the rosetting phenomenon, which occurs during the life cycle of the parasite in red blood cells (RBCs) and promotes the binding of parasitized RBCs to healthy ones. The role of the ABO blood group antigens in relation to the phenomenon has previously only been investigated in clinical isolates obtained from malaria patients. Here, we aim to clarify their role using synthetic ABO-decorated giant unilamellar vesicles (GUVs), which serve as simple biomimetic models of RBC-size cell membranes. Our results suggest clearly and for the first time that the blood group A and O antigens have a direct impact on receptor-specific rosetting phenomena when compared to the B antigen, which only participates in rosetting to an insignificant degree. Thus, glycodecorated GUVs represent a practical tool for studying cell-surface interactions.

Tailor-made Janus lectin with dual avidity assembles glycoconjugate multilayers and crosslinks protocells

The double-faced Janus lectin, designed by assembling sialic acid and fucose-specific lectin, organize multivalent heteroglyco compounds in mulitlayered material, and glycosylated protocells in prototissues.

We engineered the first chimeric, bispecific lectin, with two rationally oriented and distinct recognition surfaces. This lectin, coined Janus lectin in allusion to the two-faced roman god, is able to bind independently to both fucosylated and sialylated glycoconjugates. The multivalent presentation of binding sites on each face of the Janus lectin is very efficient, resulting in avidities in the low nanomolar range for both fucosylated and sialylated surfaces. Moreover, novel heterovalent, bifunctional glycoclusters were synthetized that match the topology of the Janus lectin. Based on these tools, we constructed organized and controlled supramolecular architectures by assembling Janus lectin and glycocompound layer-by-layer. Furthermore, the Janus lectin was employed as biomolecular linker to organize protocells made from giant unilamellar vesicles of different nature, to more complex prototissues. In summary, tailor-made Janus lectins open wide possibilities for creating biomimetic matrices or artificial tissues.