Chemoenzymatic Preparation of a Campylobacter jejuni Lipid-Linked Heptasaccharide on an Azide-Linked Polyisoprenoid

Complex poly- and oligosaccharides on the surface of bacteria provide a unique fingerprint to different strains of pathogenic and symbiotic microbes that could be exploited for therapeutics or sensors selective for specific glycans. To discover reagents that can selectively interact with specific bacterial glycans, a system for both the chemoenzymatic preparation and immobilization of these materials would be ideal. Bacterial glycans are typically synthesized in nature on the C55 polyisoprenoid bactoprenyl (or undecaprenyl) phosphate. However, this long-chain isoprenoid can be difficult to work with in vitro. Here, we describe the addition of a chemically functional benzylazide tag to polyisoprenoids. We have found that both the organic-soluble and water-soluble benzylazide isoprenoid can serve as a substrate for the well-characterized system responsible for Campylobacter jejuni N-linked heptasaccharide assembly. Using the organic-soluble analogue, we demonstrate the use of an N-acetyl-glucosamine epimerase that can be used to lower the cost of glycan assembly, and using the water-soluble analogue, we demonstrate the immobilization of the C. jejuni heptasaccharide on magnetic beads. These conjugated beads are then shown to interact with soybean agglutinin, a lectin known to interact with N-acetyl-galactosamine in the C. jejuni heptasaccharide. The methods provided could be used for a wide variety of applications including the discovery of new glycan-interacting partners.

Click Chemistry with Cyclopentadiene

Cyclopentadiene is one of the most reactive dienes in normal electron-demand Diels-Alder reactions. The high reactivities and yields of cyclopentadiene cycloadditions make them ideal as click reactions. In this review, we discuss the history of the cyclopentadiene cycloaddition as well as applications of cyclopentadiene click reactions. Our emphasis is on experimental and theoretical studies on the reactivity and stability of cyclopentadiene and cyclopentadiene derivatives.

Glycoprotein- and Lectin-Based Approaches for Detection of Pathogens

Infectious diseases alone are estimated to result in approximately 40% of the 50 million total annual deaths globally. The importance of basic research in the control of emerging and re-emerging diseases cannot be overemphasized. However, new nanotechnology-based methodologies exploiting unique surface-located glycoproteins or their patterns can be exploited to detect pathogens at the point of use or on-site with high specificity and sensitivity. These technologies will, therefore, affect our ability in the future to more accurately assess risk. The critical challenge is making these new methodologies cost-effective, as well as simple to use, for the diagnostics industry and public healthcare providers. Miniaturization of biochemical assays in lab-on-a-chip devices has emerged as a promising tool. Miniaturization has the potential to shape modern biotechnology and how point-of-care testing of infectious diseases will be performed by developing smart microdevices that require minute amounts of sample and reagents and are cost-effective, robust, and sensitive and specific. The current review provides a short overview of some of the futuristic approaches using simple molecular interactions between glycoproteins and glycoprotein-binding molecules for the efficient and rapid detection of various pathogens at the point of use, advancing the emerging field of glyconanodiagnostics.

Immobilization of glycans on solid surfaces for application in glycomics

Carbohydrates are an important class of biomolecules which are involved in a multitude of cellular functions. In the field of glycomics, the structure and function of various carbohydrates, oligosaccharides, glycans and their conjugates are constantly under investigation. In the continuing quest to understand the roles of carbohydrates in their interactions with proteins, immunogens, and other cell-surface carbohydrates, scientists have developed methods for observing the effects of specific saccharide sequences on various cellular components. Carbohydrate immobilization has allowed researchers to study the impact of specific sequences, leading to a deeper understanding of many cellular processes. The goal of this review is to highlight the chemical reactions and interactions that have been used for glycan immobilization.

Real-time, label-free characterization of oligosaccharide-binding proteins using carbohydrate microarrays and an ellipsometry-based biosensor

Carbohydrates present on cell surfaces mediate cell behavior through interactions with other biomolecules. Due to their structural complexity, diversity, and heterogeneity, it is difficult to fully characterize a variety of carbohydrates and their binding partners. As a result, novel technologies for glycomics applications have been developed, including carbohydrate microarrays and label-free detection methods. In this paper, we report using the combination of oligosaccharide microarrays and the label-free oblique-incidence reflectivity difference (OI-RD) microscopy for real-time characterization of oligosaccharide binding proteins. Aminated human milk oligosaccharides were immobilized on epoxy-coated glass substrates as microarrays for reactions with Family 1 of solute binding proteins from Bifidobacterium longum subsp. infantis (B. infantis). Binding affinities of these protein-oligosaccharide interactions showed preferences of Family 1 of solute binding proteins to host glycans, which helps in characterizing the complex process of human milk oligosaccharides foraging by B. infantis.

Carbohydrate microarrays by microcontact printing

This Article describes the preparation of carbohydrate microarrays by the immobilization of carbohydrates via microcontact printing (microCP) on glass and silicon substrates. To this end, diene-modified carbohydrates (galactose, glucose, mannose, lactose, and maltose) were printed on maleimide-terminated self-assembled monolayers (SAMs). A Diels-Alder reaction occurred exclusively in the contact area between stamp and substrate and resulted in a carbohydrate pattern on the substrate. It was found that cyclopentadiene-functionalized carbohydrates could be printed within minutes at room temperature, whereas furan-functionalized carbohydrates required long printing times and high temperatures. By successive printing, microstructured arrays of up to three different carbohydrates could be produced. Immobilization and patterning of the carbohydrates on the surfaces was investigated with contact angle measurements, X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (TOF-SIMS), and fluorescence microscopy. Furthermore, the lectins concanavalin A (ConA) and peanut agglutinin (PNA) bind to the microarrays, and the printed carbohydrates retain their characteristic selectivity toward these proteins.

Carbohydrate cluster microarrays fabricated on three-dimensional dendrimeric platforms for functional glycomics exploration

We reported here a novel, ready-to-use bioarray platform and methodology for construction of sensitive carbohydrate cluster microarrays. This technology utilizes a three-dimensional (3-D) poly(amidoamine) starburst dendrimer monolayer assembled on glass surface, which is functionalized with terminal aminooxy and hydrazide groups for site-specific coupling of carbohydrates. A wide range of saccharides, including monosaccharides, oligosaccharides and polysaccharides of diverse structures, are applicable for the 3-D bioarray platform without prior chemical derivatization. The process of carbohydrate coupling is effectively accelerated by microwave radiation energy. The carbohydrate concentration required for microarray fabrication is substantially reduced using this technology. Importantly, this bioarray platform presents sugar chains in defined orientation and cluster configurations. It is, thus, uniquely useful for exploration of the structural and conformational diversities of glyco-epitope and their functional properties.

Silica Colloidal Crystals for Enhanced Fluorescence Detection in Microarrays

Silica colloidal crystals were investigated for their potential as high surface area materials to enhance sensitivity over planar surfaces for microarrays using fluorescence detection. A relation was derived showing how crystal thickness and transmission, as well as colloid size, combine to determine the optically accessible surface area for enhancing sensitivity. Experimentally, crystals of 250-nm colloids were prepared with thicknesses determined by SEM to be 1.6, 4.2, and 11.0 microm. The material was sintered at 1000 degrees C to make it durable without affecting the crystalline structure, as confirmed by SEM. UV/visible spectrometry showed the depth of penetration (1/e) to be 8.4 microm at 488 nm for these materials. Fluorescein-labeled streptavidin and biotin were used as a model ligand-receptor pair. For the fluorescence measurements, biotin was covalently bonded to the silica surfaces, and the fluorescence was detected from the captured streptavidin-fluorescein. The observed fluorescence enhancement agreed well with the theory developed here. Compared to a planar surface, the colloidal crystal of 11.0 microm in thickness enhanced the fluorescence by nearly a factor of 80, with only a 0.3% increase in fluorescence background.