Synthesis of Gold Glyconanoparticles: Possible Probes for the Exploration of Carbohydrate-Mediated Self-Recognition of Marine Sponge Cells

A brief insight to the role of glyconanotechnology in modern day diagnostics and therapeutics

Carbohydrate-protein and carbohydrate-carbohydrate interactions are very important for various biological processes. Although the magnitude of these interactions is low compared to that of protein-protein interaction, the magnitude can be boosted by multivalent approach known as glycocluster effect. Nanoparticle platform is one of the best ways to present diverse glycoforms in multivalent manner and thus, the field of glyconanotechnology has emerged as an important field of research considering their potential applications in diagnostics and therapeutics. Considerable advances in the field have been achieved through development of novel techniques, use of diverse metallic and non-metallic cores for better efficacy and application of ever-increasing number of carbohydrate ligands for site-specific interaction. The present review encompasses the recent developments in the area of glyconanotechnology and their future promise as diagnostic and therapeutic tools.

Recent Advances in the Application of Glycan-Modified Self-Assembled Monolayers

Glycans have many important roles in human health and disease in processes such as infection, fertilization, cellular development, cellular adhesion, cancer metastasis and immune system response. The presentation of glycan structures on surfaces for screening of their interaction with protein binding partners, interactions with individual cells, and development of bioassays is an actively developing field. Self-assembled monolayers (SAMs) of glycan terminated alkanethiols on gold have found application in many of these areas. Additionally, more complex structures such as glycan modified polymers on gold surfaces have provided new routes for multivalent glycan presentation. Glycans have also been conjugated to monolayers formed on other useful substrates such as glass or silicon wafers. SAMs have been formed both by direct immobilization of glycan terminated alkanethiols and by conjugation of glycans to pre-formed SAMs with reactive terminal groups. The structure of the SAMs has been characterized using a range of methods including surface spectroscopy, scanning probe microscopy, and electrochemical methods. The binding of proteins to these SAMs has been followed using methods including surface plasmon resonance and electrochemical techniques such as impedance spectroscopy. In this chapter, we will seek to review the recent literature concerning SAMs containing terminal glycans, with a focus on their biomolecular interactions. The applications of these glycan-modified SAMs to the screening and study of protein and cellular binding and to biosensor and assay development will be reviewed.

Recent applications of click chemistry for the functionalization of gold nanoparticles and their conversion to glyco-gold nanoparticles

Glycoscience, despite its myriad of challenges, promises to unravel the causes of, potential new detection methods for, and novel therapeutic strategies against, many disease states. In the last two decades, glyco-gold nanoparticles have emerged as one of several potential new tools for glycoscientists. Glyco-gold nanoparticles consist of the unique structural combination of a gold nanoparticle core and an outer-shell comprising multivalent presentation of carbohydrates. The combination of the distinctive physicochemical properties of the gold core and the biological function/activity of the carbohydrates makes glyco-gold nanoparticles a valuable tool in glycoscience. In this review we present recent advances made in the use of one type of click chemistry, namely the azide-alkyne Huisgen cycloaddition, for the functionalization of gold nanoparticles and their conversion to glyco-gold nanoparticles.

Glyconanomaterials: Emerging applications in biomedical research

Carbohydrates constitute the most abundant organic matter in nature, serving as structural components and energy sources, and mediating a wide range of cellular activities. The emergence of nanomaterials with distinct optical, magnetic, and electronic properties has witnessed a rapid adoption of these materials for biomedical research and applications. Nanomaterials of various shapes and sizes having large specific surface areas can be used as multivalent scaffolds to present carbohydrate ligands. The resulting glyconanomaterials effectively amplify the glycan-mediated interactions, making it possible to use these materials for sensing, imaging, diagnosis, and therapy. In this review, we summarize the synthetic strategies for the preparation of various glyconanomaterials. Examples are given where these glyconanomaterials have been used in sensing and differentiation of proteins and cells, as well as in imaging glycan-medicated cellular responses.

Model system for cell adhesion mediated by weak carbohydrate-carbohydrate interactions

The multivalent carbohydrate-carbohydrate interaction between membrane-anchored epitopes derived from the marine sponge Microciona prolifera has been explored by colloidal probe microscopy. An in situ coupling of sulfated and non-sulfated disaccharides to membrane-coated surfaces was employed to mimic native cell-cell contacts.The dynamic strength of the homomeric self-association was measured as a function of calcium ions and loading rate. A deterministic model was used to estimate the basic energy landscape and number of participating bonds in the contact zone.

Synthesis of Neoglycoconjugates Containing 4-Amino-4-deoxy-l-arabinose Epitopes Corresponding to the Inner Core of Burkholderia and Proteus Lipopolysaccharides

Disaccharides that contain 3-deoxy-d-manno-oct-2-ulosonic acid (Kdo) and d-glycero-d-talo-oct-2-ulosonic acid (Ko) substituted at the 8-position by 4-amino-4-deoxy-β-l-arabinopyranosyl (Ara4N) residues have been prepared. Coupling an N-phenyltrifluoroacetimidate-4-azido-4-deoxy-l-arabinosylglycosyl donor to acetyl-protected allyl glycosides of Kdo and Ko afforded anomeric mixtures of disaccharide products in 74 and 90 % yield, respectively, which were separated by chromatography. Further extension of an intermediate Ara4N-(1→8)-Kdo disaccharide acceptor, which capitalized on a regioselective glycosylation with a Kdo bromide donor under Helferich conditions, afforded the branched trisaccharide α-Kdo-(2→4)[β-l-Ara4N-(1→8)]-α-Kdo derivative. Deprotection of the protected di- and trisaccharide allyl glycosides was accomplished by TiCl₄-promoted benzyl ether cleavage followed by the removal of ester groups and reduction of the azido group with thiol or Staudinger reagents, respectively. The reaction of the anomeric allyl group with 1,3-propanedithiol under radical conditions afforded the thioether-bridged spacer glycosides, which were efficiently coupled to maleimide-activated bovine serum albumin. The neoglycoconjugates serve as immunoreagents with specificity for inner core epitopes of Burkholderia and Proteus lipopolysaccharides.

A convenient method for synthesis of glyconanoparticles for colorimetric measuring carbohydrate-protein interactions

Carbohydrate functionalized nanoparticles, i.e., the glyconanoparticles, have wide application ranging from studies of carbohydrate-protein interactions, in vivo cell imaging, biolabeling, etc. Currently reported methods for preparation of glyconanoparticles require multi-step modifications of carbohydrates moieties to conjugate to nanoparticle surface. However, the required synthetic manipulations are difficult and time consuming. We report herewith a simple and versatile method for preparing glyconanoparticles. This method is based on the utilization of clean and convenient microwave irradiation energy for one-step, site-specific conjugation of unmodified carbohydrates onto hydrazide-functionalized Au nanoparticles. A colorimetric assay that utilizes the ensemble of gold glyconanoparticles and Concanavalin A (ConA) was also presented. This feasible assay system was developed to analyze multivalent interactions and to determine the dissociation constant (K(d)) for five kind of Au glyconanoparticles with lectin. Surface plasmon changes of the Au glyconanoparticles as a function of lectin-carbohydrate interactions were measured and the dissociation constants were determined based on non-linear curve fitting. The strength of the interaction of carbohydrates with ConA was found to be as follows: maltose>mannose>glucose>lactose>MAN5.

Assessing carbohydrate-carbohydrate interactions by NMR spectroscopy: the trisaccharide epitope from the marine sponge Microciona prolifera

WEAK RECOGNITION PROCESSES: Weak calcium-mediated carbohydrate-carbohydrate interactions have been detected by DOSY and TRNOESY NMR methods by employing a gold glyconanoparticle as a multivalent system. In addition, 3D models of trisaccharide-Ca(II)-trisaccharide complexes based on results from molecular dynamics simulations are proposed. Diffusion-ordered NMR spectroscopy (DOSY-NMR) and TR-NOESY-NMR experiments are used to detect ligand binding to macromolecular receptors. These techniques have been applied to detect weak carbohydrate-carbohydrate self-recognition in solution, making use of sugar-decorated gold nanoparticles as the "macromolecule" and the same carbohydrate as the ligand. Changes in the diffusion coefficient of the free carbohydrate in the presence of the glyconanoparticle (only with Ca(II) ions in the sample solution), as well as changes in the sign of the sugar NOE peaks--positive for the free sugar (in the presence or absence of Ca(II)) and negative for the sugar only in the simultaneous presence of the glyconanoparticle and Ca(II) ions--have been taken as proof of weak Ca(II)-mediated carbohydrate-carbohydrate interactions in solution. Although different methods such as SPR, TEM, and AFM have been used in the past to detect carbohydrate-carbohydrate interactions with the aid of gold nanoparticles and gold selfassembled monolayers, they are restricted to high-affinity ranges. The methods used in this study allow expansion of the number of techniques to tackle this relevant biological problem, also for approaching ligand-receptor interactions below the high-affinity range. Additionally, 3D models of trisaccharide-Ca(II)-trisaccharide complexes based on results from molecular dynamics simulations are proposed.

Glyconanoparticles allow pre-symptomatic in vivo imaging of brain disease

Initial recruitment of leukocytes in inflammation associated with diseases such as multiple sclerosis (MS), ischemic stroke, and HIV-related dementia, takes place across intact, but activated brain endothelium. It is therefore undetectable to symptom-based diagnoses and cannot be observed by conventional imaging techniques, which rely on increased permeability of the blood-brain barrier (BBB) in later stages of disease. Specific visualization of the early-activated cerebral endothelium would provide a powerful tool for the presymptomatic diagnosis of brain disease and evaluation of new therapies. Here, we present the design, construction and in vivo application of carbohydrate-functionalized nanoparticles that allow direct detection of endothelial markers E-/P-selectin (CD62E/CD62P) in acute inflammation. These first examples of MRI-visible glyconanoparticles display multiple copies of the natural complex glycan ligand of selectins. Their resulting sensitivity and binding selectivity has allowed acute detection of disease in mammals with beneficial implications for treatment of an expanding patient population suffering from neurological disease.

Adhesion forces in the self-recognition of oligosaccharide epitopes of the proteoglycan aggregation factor of the marine sponge Microciona prolifera

Cell aggregation in the marine sponge Microciona prolifera is mediated by a multimillion molecular-mass aggregation factor, termed MAF. Earlier investigations revealed that the cell aggregation activity of MAF depends on two functional domains: (i) a Ca(2+)-independent cell-binding domain and (ii) a Ca(2+)-dependent proteoglycan self-interaction domain. Structural analysis of involved carbohydrate fragments of the proteoglycan in the self-association established a sulfated disaccharide beta-D: -GlcpNAc3S-(1-->3)-alpha-L: -Fucp and a pyruvated trisaccharide beta-D: -Galp4,6(R)Pyr-(1-->4)-beta-D: -GlcpNAc-(1-->3)-alpha-L: -Fucp. Recent UV, SPR, and TEM studies, using BSA conjugates and gold nanoparticles of the synthetic sulfated disaccharide, clearly demonstrated self-recognition on the disaccharide level in the presence of Ca(2+)-ions. To determine binding forces of the carbohydrate-carbohydrate interactions for both synthetic MAF oligosaccharides, atomic force microscopy (AFM) studies were carried out. It turned out that, in the presence of Ca(2+)-ions, the force required to separate the tip and sample coated with a self-assembling monolayer of thiol-spacer-containing beta-D: -GlcpNAc-(1-->3)-alpha-L: -Fucp-(1-->O)(CH(2))(3)S(CH(2))(6)S- was found to be quantized in integer multiples of 30 +/- 6 pN. No binding was observed between the two monolayers in the absence of Ca(2+)-ions. Cd(2+)-ions could partially induce the self-interaction. In contrast, similar AFM experiments with thiol-spacer-containing beta-D: -Galp4,6(R)Pyr-(1-->4)-beta-D: -GlcpNAc-(1-->3)-alpha-L: -Fucp-(1-->O)(CH(2))(3)S(CH(2))(6)S- did not show a binding in the presence of Ca(2+)-ions. Also TEM experiments of gold nanoparticles coated with the pyruvated trisaccharide could not make visible aggregation in the presence of Ca(2+)-ions. It is suggested that the self-interaction between the sulfated disaccharide fragments is stronger than that between the pyruvated trisaccharide.

Varied presentation of the Thomsen-Friedenreich disaccharide tumor-associated carbohydrate antigen on gold nanoparticles

Three-dimensional self-assembled monolayers of gold coated with the Thomsen-Friedenreich antigen (TF(ag)) disaccharide (beta-Galp-(1-->3)-GalpNAc) in a variety of presentations have been prepared and characterized. Anomalies in the size distribution of our originally synthesized TF(ag)-bearing nanoparticles as shown in dynamic light scattering experiments prompted us to explore the effect of antigen density on the uniformity of the particles. Gold nanoparticles containing a range of densities 'diluted' with copies of the PEG-thiol spacer unit showed that lower antigen density affords more uniform particles. We also wanted to study the constitution of the actual antigen by synthesizing nanoparticles not only with the linker-extended disaccharide, but also within the context of the surrounding peptide sequence where it may be presented in vivo. The synthesis of TF(ag)-containing glycopeptide thiols based on a mucin peptide repeating unit were prepared, assembled into gold nanoparticles and their physical properties evaluated. These novel multivalent tools should prove extremely useful in exploring the binding properties and immune response to this important carbohydrate antigen.

Globotriose-functionalized gold nanoparticles as multivalent probes for Shiga-like toxin

Compared to monovalent carbohydrates, multivalent carbohydrate ligands exhibit significantly enhanced binding affinities to their interacting proteins. Here, we report globotriose (P(k) ligand)-functionalized gold nanoparticle (AuNP) probes for the investigation of multivalent interactions with the B(5) subunit of Shiga-like toxin I (B-Slt). Six P(k)-ligand-encapsulated AuNPs (P(k)-AuNPs) of varying particle size and linker length were synthesized and evaluated for their potential as multivalent affinity probes by using a surface plasmon resonance competition assay. The affinity of these probes for the interacting proteins was greatly affected by nanoparticle size, linker length, and ligand density on nanoparticle surface. For example, the 20-nm 20-P(k)-l-AuNP, which had a relatively long linker showed a >10(8)-fold increase in affinity compared with the mono P(k) ligand. This intrinsic high-affinity AuNP probe specifically captured the recombinant B-Slt from Escherichia coli lysate, and the resulting purity of the B-Slt was >95 %. We also developed a robust P(k)-AuNP-based detection method for Slt-I by combining the technique with silver enhancement.

Multiutility sophorolipids as nanoparticle capping agents: synthesis of stable and water dispersible Co nanoparticles

Sophorolipids are a class of glycolipids that can be obtained from fatty acids by simply treating them with yeast cells (Candida bombicola, ATCC 22214) and glucose. In this letter, we demonstrate the application of sophorolipids obtained from oleic acid as a capping agent for Co nanoparticles. Upon capping the nanoparticle surface, the sugar moiety of these sophorolipids is exposed to the solvent environment, making the nanoparticles stable and water-redispersible.

Solid-phase chemical tools for glycobiology

Techniques involving solid supports have played crucial roles in the development of genomics, proteomics, and in molecular biology in general. Similarly, methods for immobilization or attachment to surfaces and resins have become ubiquitous in sequencing, synthesis, analysis, and screening of oligonucleotides, peptides, and proteins. However, solid-phase tools have been employed to a much lesser extent in glycobiology and glycomics. This review provides a comprehensive overview of solid-phase chemical tools for glycobiology including methodologies and applications. We provide a broad perspective of different approaches, including some well-established ones, such as immobilization in microtiter plates and to cross-linked polymers. Emerging areas such as glycan microarrays and glycan sequencing, quantum dots, and gold nanoparticles for nanobioscience applications are also discussed. The applications reviewed here include enzymology, immunology, elucidation of biosynthesis, and systems biology, as well as first steps toward solid-supported sequencing. From these methods and applications emerge a general vision for the use of solid-phase chemical tools in glycobiology.

Analysis of carbohydrate-carbohydrate interactions using gold glyconanoparticles and oligosaccharide self-assembling monolayers

Carbohydrates are the most extended structures exposed at the surface of most cells. These carbohydrate chains, when arranged in polyvalent clusters, offer a rich supply of low-affinity binding sites, making them a reliable and flexible system to regulate cell adhesion and recognition. The very first model system for cell-cell recognition by means of carbohydrate-carbohydrate interactions in the animal kingdom came from a primitive invertebrate animal: the marine sponge. During the past 50 years, studies have shown that highly repetitive carbohydrate motives on extracellular proteoglycan supramolecular complexes of marine sponge cells are involved in the species-specific adhesion. In this chapter, some glyconanotechnology procedures are described for the detailed investigation of the role of a carbohydrate epitope in the marine sponge cell recognition. The various protocols are generally applicable in other areas of glycoscience.

Glyconanoparticles: types, synthesis and applications in glycoscience, biomedicine and material science

Nanoparticles are the subject of numerous papers and reports and are full of promises for electronic, optical, magnetic and biomedical applications. Although metallic nanoparticles have been functionalized with peptides, proteins and DNA during the last 20 years, carbohydrates have not been used with this purpose until 2001. Since the first synthesis of gold nanoparticles functionalized with carbohydrates (glyconanoparticles) was reported, the number of published articles has considerably increased. This article reviews progress in the development of nanoparticles functionalized with biological relevant oligosaccharides. The glyconanoparticles constitute a good bio-mimetic model of carbohydrate presentation at the cell surface, and maybe, excellent tools for Glycobiology, Biomedicine and Material Science investigations.