Studying the interaction of alpha-gal carbohydrate antigen and proteins by quartz-crystal microbalance

Validation of Selective Capture of Fimbriated Uropathogenic Escherichia coli by a Label-free Engineering Detection System Using Mannosylated Surfaces

Label-free detection of pathogens is of major concern to the microbiologist community. Most procedures require several steps and amplification techniques. Carbohydrates are well-established receptors for host-pathogen interactions, which can be amplified using glycodendritic architectures on the basis of multivalent binding interactions. Given that uropathogenic Escherichia coli bacterial FimH is based on such mannopyranoside-binding interactions, we demonstrate herein that synthetic monomeric and trimeric thiolated α-d-mannosides can be effectively bound to gold substrate-functionalized self-assembled monolayers (SAMs) preactivated with maleimide functionalities. Mannosides grafted onto SAMs were followed using Quartz Crystal Microbalance with Dissipation (QCM-D). Binding recognition efficiency was first evaluated using the plant lectin from Canavalia ensiformis (ConA) also using QCM-D. We showed a direct correlation between the amount of mannoside bound and the lectin attachment. Even though there was less trimer bound (nM/cm²) to the surface, we observed a 7-fold higher amount of lectin anchoring, thus further demonstrating the value of the multivalent interactions. We next examined the relative fimbriated E. coli selective adhesion/capture to either the monomeric or the trimeric mannoside bound to the surface. Our results established the successful engineering of the surfaces to show E. coli adhesion via specific mannopyranoside binding but unexpectedly, the monomeric derivative was more efficient than the trimeric analog, which could be explained by steric hindrance. This approach strongly suggests that it could be broadly applicable to other Gram-negative bacteria sharing analogous carbohydrate-dependent binding interactions.

Micro- and nano-structure based oligonucleotide sensors

This paper presents a review of micro- and nano-structure based oligonucleotide detection and quantification techniques. The characteristics of such devices make them very attractive for Point-of-Care or On-Site-Testing biosensing applications. Their small scale means that they can be robust and portable, their compatibility with modern CMOS electronics means that they can easily be incorporated into hand-held devices and their suitability for mass production means that, out of the different approaches to oligonucleotide detection, they are the most suitable for commercialisation. This review discusses the advantages of micro- and nano-structure based sensors and covers the various oligonucleotide detection techniques that have been developed to date. These include: Bulk Acoustic Wave and Surface Acoustic Wave devices, micro- and nano-cantilever sensors, gene Field Effect Transistors, and nanowire and nanopore based sensors. Oligonucleotide immobilisation techniques are also discussed.

A highly sensitive quartz crystal microbalance immunosensor based on magnetic bead-supported bienzymes catalyzed mass enhancement strategy

A highly sensitive quartz crystal microbalance (QCM) immunosensor based on magnetic bead-supported bienzyme catalyzed mass enhanced strategy was developed for the detection of human immunoglobulin G (hIgG) protein. The high sensitive detection was achieved by increasing the deposited mass on the QCM crystal through the enhanced precipitation of 4-chloro-1-naphthol (CN) using higher amounts of horseradish peroxidase (HRP) and glucose oxidase (GOx) bienzymes attached on the magnetic beads (MB). The protein A (PA) and capture antibody (monoclonal anti-human IgG antibody produced in mouse, Ab1)-based QCM probe and the detection antibody (anti-human IgG antibody produced in goat, Ab2)-based MB/HRP/GOx bienzymatic bioconjugates were characterized using scanning electron microscope, transmission electron microscope, cyclic voltammetry, and electrochemical impedance spectroscopy techniques. Under the optimized experimental condition, the linear range and the detection limit of hIgG immunosensor were determined to be 5.0pg/mL-20.0ng/mL and 5.0±0.18pg/mL, respectively. The applicability of the present hIgG immunosensor was examined in hIgG spiked human serum samples and excellent recoveries of hIgG were obtained.

Surface-bound cytomimetic assembly based on chemoselective and biocompatible immobilization and further modification of intact liposome

A surface-bound cytomimetic assembly based on chemically selective and biocompatible immobilization and further modification of intact liposome is described. Liposomes carrying PEG-triphenylphosphine were chemoselectively immobilized onto azide-modified glass slides through Staudinger ligation, followed by modification with azide-modified lactose as a model biomolecule through Staudinger ligation to afford the surface-bound cytomimetic assembly. The intact liposome immobilized and modified and its protein binding activity were confirmed by fluorescence imaging, fluorescent dye releasing kinetics, and AFM techniques. The resultant surface-bound cytomimetic assembly showed sustained stability and fluorescent dye releasing kinetics and specific protein binding activity. The reported method provides a robust platform for preparation of a complex immobilized liposome system with multifunctional components, which mimics the cell surface in both geographical and content features and thus will find important biomedical applications.

Multivalent interaction-based carbohydrate biosensors for signal amplification

Multivalent interaction between boronic acids immobilized on quartz crystal microbalance (QCM) sensor surface and the carbohydrates modified Au-nanoparticle (AuNP) has been demonstrated for the development of a sensitive carbohydrate biosensor. Briefly, a boronic acid-containing polymer (boropolymer) as multivalent carbohydrate receptor was oriented immobilized on the cysteamine coated electrode through isourea bond formation. Carbohydrates were conjugated to AuNPs to generate a multivalent carbohydrates moiety to amplify the response signal. Thus, the binding of the carbohydrate conjugated AuNPs to the boropolymer surface are multivalent which could simultaneously increase the binding affinity and specificity. We systematically studied the binding between five carbohydrates conjugated AuNPs and the boropolymer. Our studies show that the associate constant (K(a)) was in the order of fucose Collapse

Key Words

• carbohydrate biosensor
• multivalent interaction
• boronic acid

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MESH Headings

• Biosensing Techniques/methods
• Boronic Acids
• Carbohydrate Metabolism
• Carbohydrates/chemistry
• Electrochemical Techniques
• Gold
• Metal Nanoparticles
• Molecular Structure
• Polymers/chemistry
• Quartz Crystal Microbalance Techniques

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Grants

• EB000672 NIBIB NIH HHS
• R21 EB009513 NIBIB NIH HHS
• R21 EB000672 NIBIB NIH HHS
• R33 EB000672 NIBIB NIH HHS
• R21 EB009513-01A1 NIBIB NIH HHS

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Affiliation(s)

Yanyan Wang Department of Chemistry, Oakland University, Rochester, Michigan 48309, USA The key Laboratory of Bioactive Materials Ministry of Education, College of Life Sciences, Nankai University, Tianjin 300071, China
Srinivas Chalagalla Department of Chemistry, Cleveland State University, Cleveland, Ohio 44115
Tiehai Li College of Pharmacy, Nankai University, Tianjin 300071, China
Xue-long Sun Department of Chemistry, Cleveland State University, Cleveland, Ohio 44115
Wei Zhao College of Pharmacy, Nankai University, Tianjin 300071, China
Peng Wang College of Pharmacy, Nankai University, Tianjin 300071, China
Xiangqun Zeng Department of Chemistry, Oakland University, Rochester, Michigan 48309, USA

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Electrochemical determination of carbohydrate-binding proteins using carbohydrate-stabilized gold nanoparticles and silver enhancement

A highly sensitive electrochemical lectin biosensor has been developed for the first time using carbohydrate-stabilized gold nanoparticles and silver-enhancement technique. A target lectin protein, Concanavalin A (Con A), was specifically bound to the self-assembled monolayer of thiolated mannose on a gold electrode. Mannose-stabilized gold nanoparticles were added to form a sandwich-type complex with the Con A and were followed by silver-enhancement process to coat the mannose-stabilized gold nanoparticles with silver metal. The coated metallic silver was dissolved in an acidic solution and the resulting silver ions were detected by anodic stripping voltammetry. The present lectin biosensor gave a linear response (R(2)=0.999) for Con A concentration from 0.084 μg/mL to 50.0 μg/mL with a remarkable detection limit (S/N=3) of 0.070 μg/mL, which is much lower compared to those obtained with the reported microgravimetric and colorimetric detection methods.

Synthesis and biological evaluation of sperm CD52 GPI anchor and related derivatives as binding receptors of pore-forming CAMP factor

Sperm CD52 GPI anchor and its derivatives containing different carbohydrate chains were prepared in a highly convergent fashion starting from the same properly protected phospholipidated pseudodisaccharide. Coupling this common key intermediate to various oligosaccharyl donors quickly afforded the framework of the synthetic targets, which was followed by global deprotection to furnish the desired structures. Preliminary studies on the biological properties of the synthetic GPI derivatives indicated that both the intact GPI anchor and the free phospholipidated pseudodisaccharide interacted strongly with CAMP factor, a pore-forming bacterial toxin.

Alkanethiol containing glycopolymers: A tool for the detection of lectin binding

Glycopolymers are useful macromolecules with a non-carbohydrate backbone for presenting saccharides in multivalent form. Here, glycopolymers containing mannose and alkanethiol linker were synthesized through substituting preactivated poly [N-(acryloyloxy) succinimide] (pNAS) with amine-containing monomer. With the obtained glycopolymers, a glycosurface was generated on the gold surface of quartz crystal microbalance (QCM) through self-assembled strategy by the use of alkanethiol functional group. Furthermore, the resulting glycosurface was used to detect the binding of mannose specific lectin concanavalin A (Con A).

Kinetic studies on the interactions between glycolipid biosurfactant assembled monolayers and various classes of immunoglobulins using surface plasmon resonance

Kinetic studies on the interactions between self-assembled monolayers of mannosylerythritol lipids (MELs), which are glycolipid biosurfactants abundantly produced by microorganisms, and various classes of immunoglobulins including human IgG, IgA, and IgM were performed using surface plasmon resonance (SPR). The effect of the MEL structure on the binding behavior of HIgG was examined. Assembled monolayers of MEL-A having two acetyl groups on the headgroup gave a high affinity (K(d)=1.7x10(-6)M) toward HIgG, while those of MEL-B or MEL-C having only one acetyl group at C-6' or C-4' position gave little affinity. Our kinetic analysis revealed that the binding manner of HIgG, HIgA (K(d)=2.4x10(-7)M), and HIgM (K(d)=2.2x10(-7)M) to the assembled monolayers of MEL-A is not the monovalent mode but the bivalent mode, and both the first and second rate association constants (k(a1), k(a2)) increase with an increase in the number of antibody binding sites, while those for dissociation (k(d1), k(d2)) changed little. Moreover, we succeeded in directly observing great amounts of HIgG, HIgA, and HIgM bound to MEL-A monolayers using atomic force microscopy (AFM). Finally, we found that MEL-A assembled monolayer binds toward various IgG derived from mouse, pig, rabbit, horse, goat, rat, and bovine as well as human IgG (HIgG), and the only exception was sheep IgG. These results clearly demonstrate that MEL-A assembled monolayers would be useful as noble affinity ligand system for various immunoglobulins.

Monolayers assembled from a glycolipid biosurfactant from Pseudozyma (Candida) antarctica serve as a high-affinity ligand system for immunoglobulin G and M

A carbohydrate ligand system has been developed which is composed of self-assembled monolayers (SAMs) of mannosylerythritol lipid-A (MEL-A) from Pseudozyma antarctica, serving for human immunoglobulin G and M (HIgG and HIgM). The estimated binding constants from surface plasmon resonance (SPR) measurement were Ka = 9.4 x 10(6) M(-1) for HIgG and 5.4 x 10(6) M(-1) for HIgM, respectively. The binding site was not in the Fc region of immunoglobulin but in the Fab region. Large amounts of HIgG and HIgM bound to MEL-A SAMs were directly observed by atomic force microscopy.

A survey of the 2001 to 2005 quartz crystal microbalance biosensor literature: applications of acoustic physics to the analysis of biomolecular interactions

The widespread exploitation of biosensors in the analysis of molecular recognition has its origins in the mid-1990s following the release of commercial systems based on surface plasmon resonance (SPR). More recently, platforms based on piezoelectric acoustic sensors (principally 'bulk acoustic wave' (BAW), 'thickness shear mode' (TSM) sensors or 'quartz crystal microbalances' (QCM)), have been released that are driving the publication of a large number of papers analysing binding specificities, affinities, kinetics and conformational changes associated with a molecular recognition event. This article highlights salient theoretical and practical aspects of the technologies that underpin acoustic analysis, then reviews exemplary papers in key application areas involving small molecular weight ligands, carbohydrates, proteins, nucleic acids, viruses, bacteria, cells and lipidic and polymeric interfaces. Key differentiators between optical and acoustic sensing modalities are also reviewed.

Direct Observation of Substrate−Enzyme Complexation by Surface Forces Measurement1

The substrate-enzyme complexation of heptaprenyl diphosphate synthase was directly investigated using colloidal probe atomic force microscopy (AFM) and a quartz crystal microbalance (QCM) in order to obtain new insights into the molecular mechanism of the enzyme reaction. This enzyme is composed of two dissociable subunits that exhibit a catalytic activity only when they are associated together in the presence of a cofactor, Mg2+, and a substrate, farnesyl diphosphate (FPP). The QCM measurement revealed that FPP was preferentially bound to subunit II in the presence of Mg2+, while the AFM measurement showed that the adhesive force between the subunits was observed only in the presence of both Mg2+ and FPP. This is the first direct demonstration of the specific interaction involved in the enzyme reaction. The dependence of the Mg2+ concentration on the specific interaction between subunits I and II well agreed with that on the enzyme activity of heptaprenyl diphosphate synthase. This indicated that the observed adhesive forces were indeed involved in the catalytic reaction of this enzyme. On the basis of these results, we discussed the processes involved in the substrate-enzyme complexation. The first, the substrate FPP bound to subunit II using Mg2+, followed by the formation of the subunit I-FPP-Mg2+-subunit II complex. Our study showed a very useful methodology for examining the elemental processes of biological reactions such as an enzyme reaction.

Gastrodin Interaction with Human Fibrinogen: Anticoagulant Effects and Binding Studies

In an effort to identify the anticoagulant activity of gastrodin (GAS) and to investigate the possibility of its use as a novel anticoagulant drug, the binding characteristics of GAS to human fibrinogen (Fg) were studied by using a quartz crystal microbalance (QCM) biosensor, anticoagulant animal experiments, and a molecular docking simulation. Real-time kinetic analysis with the QCM biosensor revealed that the in vitro binding of GAS to Fg was strong under physiological ionic conditions as the determined equilibrium dissociation constant (KD) was 1.94 x 10(-6) M. To check whether this strong binding may influence the natural coagulation function of Fg, the in vivo effect of GAS on the coagulation system of rats was examined. The results showed that GAS can significantly prolong the coagulation time (CT) and decrease the Fg content, while it had no effect on the activated kaolin partial thromboplastin time (KPTT) or prothrombin time (PT) in rats. To clarify the mechanism of the specific interaction, a molecular docking simulation was also performed to provide reasonable binding models for the interaction of GAS with Fg at the atomic level. GAS binds strongly to the inherent polymerization sites "a" and "b" (holes) on the Fg molecule with similar binding free energies of about -34 kJ mol(-1). Altogether, these findings confirmed first that GAS possesses anticoagulant activity and that the possible anticoagulation mechanism of GAS mainly involves its interference with the knob-to-hole interactions between fibrin molecules, thereby effectively inhibiting the formation of clots and decreasing the risk of thrombosis. The study has also shown the potential usefulness of QCM biosensor technology for the rapid screening of drug-protein interactions.

Detection of bacterial toxins with monosaccharide arrays

A large number of bacterial toxins, viruses and bacteria target carbohydrate derivatives on the cell surface to attach and gain entry into the cell. We report here the use of a monosaccharide-based array to detect protein toxins. The array-based technique provides the capability to perform simultaneous multianalyte analyses. Arrays of N-acetyl galactosamine (GalNAc) and N-acetylneuraminic acid (Neu5Ac) derivatives were immobilized on the surface of a planar waveguide and were used as receptors for protein toxins. These arrays were probed with fluorescently labeled bacterial cells and protein toxins. While Salmonella typhimurium, Listeria monocytogenes, Escherichia coli and staphylococcal enterotoxin B (SEB) did not bind to either of the monosaccharides, both cholera toxin and tetanus toxin bound to GalNAc and Neu5Ac. The results show that the binding of the toxins to the carbohydrates is density dependent and semi-selective. Both toxins were detectable at 100 ng/ml.

Single-chain fragment variable antibody piezoimmunosensors

In this paper, we describe a novel nonlabeled biosensor with high diagnostic potential for rapid and sensitive detection of antigens in complex biological samples. The biosensor comprises a piezoimmunosensor (PZ) displaying a specially constructed recombinant antibody on its surface. The recombinant single-chain fragment variable (scFv) antibody contained a cysteine within the linker amino acid sequence used to join the scFv variable heavy and light chains. The presence of cysteine induced the scFv construct to self-assemble as a densely packed rigid monolayer on the gold surface of a quartz crystal microbalance. scFv molecules in this self-assembled monolayer (SAM) exhibited a defined orientation and high areal densities, with scFv-modified microbalance surfaces displaying 35 times as many variable antigen-binding sites per square centimeter as surfaces modified with whole antibody. Experimental data show that the scFv SAM PZ is superior to Fab fragment, Fab fragment containing a free sulfhydryl group (i.e., Fab-SH), and whole antibody PZs regarding sensitivity and specificity. Because of their small uniform size (MW approximately 27000) and the ease with which they can be modified using genetic engineering, scFv's have significant advantages over whole antibodies in microbalance biosensor systems. We demonstrate here that the use of scFv containing a cysteine within the scFv linker sequence (i.e., scFv-cys) for preparation of biosensor surfaces markedly increases the density of available antigen-binding sites, yielding a system that is highly selective, rapid, and capable of detecting low concentrations of antigens in complex samples.