Accumulation of O-GlcNAc-displaying CdTe quantum dots in cells in the presence of ATP

Glyconanomaterials for biosensing applications

Nanomaterials constitute a class of structures that have unique physiochemical properties and are excellent scaffolds for presenting carbohydrates, important biomolecules that mediate a wide variety of important biological events. The fabrication of carbohydrate-presenting nanomaterials, glyconanomaterials, is of high interest and utility, combining the features of nanoscale objects with biomolecular recognition. The structures can also produce strong multivalent effects, where the nanomaterial scaffold greatly enhances the relatively weak affinities of single carbohydrate ligands to the corresponding receptors, and effectively amplifies the carbohydrate-mediated interactions. Glyconanomaterials are thus an appealing platform for biosensing applications. In this review, we discuss the chemistry for conjugation of carbohydrates to nanomaterials, summarize strategies, and tabulate examples of applying glyconanomaterials in in vitro and in vivo sensing applications of proteins, microbes, and cells. The limitations and future perspectives of these emerging glyconanomaterials sensing systems are furthermore discussed.

Cadmium-free sugar-chain-immobilized fluorescent nanoparticles containing low-toxicity ZnS-AgInS2 cores for probing lectin and cells

Sugar chains play a significant role in various biological processes through sugar chain-protein and sugar chain-sugar chain interactions. To date, various tools for analyzing sugar chains biofunctions have been developed. Fluorescent nanoparticles (FNPs) functionalized with carbohydrate, such as quantum dots (QDs), are an attractive imaging tool for analyzing carbohydrate biofunctions in vitro and in vivo. Most FNPs, however, consist of highly toxic elements such as cadmium, tellurium, selenium, and so on, causing problems in long-term bioimaging because of their cytotoxicity. In this study, we developed cadmium-free sugar-chain-immobilized fluorescent nanoparticles (SFNPs) using ZnS-AgInS2 (ZAIS) solid solution nanoparticles (NPs) of low or negligible toxicity as core components, and investigated their bioavailability and cytotoxicity. SFNPs were prepared by mixing our originally developed sugar-chain-ligand conjugates with ZAIS/ZnS core/shell NPs. In binding experiments with lectin, the obtained ZAIS/ZnS SFNPs interacted with an appropriate lectin to give specific aggregates, and their binding interaction was visually and/or spectroscopically detected. In addition, these SFNPs were successfully utilized for cytometry analysis and cellular imaging in which the cell was found to possess different sugar-binding properties. The results of the cytotoxicity assay indicated that SFNPs containing ZAIS/ZnS have much lower toxicity than those containing cadmium. These data strongly suggest that our designed SFNPs can be widely utilized in various biosensing applications involved in carbohydrates.

Hydrophilic gold nanoparticles adaptable for hydrophobic solvents

Surface ligand molecules enabling gold nanoparticles to disperse in both polar and nonpolar solvents through changes in conformation are presented. Gold nanoparticles coated with alkyl-head-capped PEG derivatives were initially well dispersed in water through exposure of the PEG residue (bent form). When chloroform was added to the aqueous solution of gold nanoparticles, the gold nanoparticles were transferred from an aqueous to a chloroform phase through exposure of the alkyl-head residue (straight form). The conformational change (bent to straight form) of immobilized ligands in response to the polarity of the solvents was supported by NMR analyses and water contact angles.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: an update for 2007-2008

This review is the fifth update of the original review, published in 1999, on the application of MALDI mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2008. The first section of the review covers fundamental studies, fragmentation of carbohydrate ions, use of derivatives and new software developments for analysis of carbohydrate spectra. Among newer areas of method development are glycan arrays, MALDI imaging and the use of ion mobility spectrometry. The second section of the review discusses applications of MALDI MS to the analysis of different types of carbohydrate. Specific compound classes that are covered include carbohydrate polymers from plants, N- and O-linked glycans from glycoproteins, biopharmaceuticals, glycated proteins, glycolipids, glycosides and various other natural products. There is a short section on the use of MALDI mass spectrometry for the study of enzymes involved in glycan processing and a section on the use of MALDI MS to monitor products of the chemical synthesis of carbohydrates with emphasis on carbohydrate-protein complexes and glycodendrimers. Corresponding analyses by electrospray ionization now appear to outnumber those performed by MALDI and the amount of literature makes a comprehensive review on this technique impractical. However, most of the work relating to sample preparation and glycan synthesis is equally relevant to electrospray and, consequently, those proposing analyses by electrospray should also find material in this review of interest.

Quantum dots to tail single bio-molecules inside living cells

In the last two decades, the single particle and single molecule approach became more and more popular to investigate the activity and the mechano-chemical properties of biological molecules. The inherent limit of these assays was that the molecules of interest were observed in vitro, out of their natural environment, the cell. Several recent works have shown the possibility to overcome this limit, to extend this approach to living cells and to observe the details of many cellular processes at the molecular level. In this review we discuss the use of semiconductor quantum dots to perform single particle and single molecule tracking in the cell. We refer to other articles for the technical aspects of this method. Here, after an introduction on the advantages provided by these nanoparticles, we restrict ourselves to some examples, mainly related to intracellular transport and molecular motor activity. These will illustrate the important role played by semiconductor quantum dots as fluorescent nano-reporters in in cell single molecule approach in modern biology and biophysics.

ENHANCED ACCUMULATION OF CARBOHYDRATE-DISPLAYING CdTe QUANTUM DOTS IN CELLS RESPONDING TO CELLULAR CHEMICAL STRESSES

We propose a novel stress sensing methods using water soluble, sugar-displaying quantum dot and digitonin-permeabilized semi-intact HeLa cells. The amount of GlcNAc -QDs (N-acetylglucosamine-displaying quantum dots) binding to heavy metal ion exposed cells was investigated by fluorescence intensity, and it increased in a dose-dependent manner. This result suggests that GlcNAc -QD could be applied for a new stress sensing probe.

Arginine 469 is a pivotal residue for the Hsc70-GlcNAc-binding property

The members of the 70kDa-heat shock proteins (HSP70) family play numerous fundamental functions in the cell such as promoting the assembly of multimeric complexes or helping the correct folding of nascent proteins to take place. In numerous previous studies we demonstrated that Hsp70 and its constitutive isoform Hsc70 are endowed of a GlcNAc-binding activity. The molecular modeling of the substrate binding domain of Hsc70 and in silico docking experiments using Ser/Thr-O-GlcNAc motifs allowed to define the potential carbohydrate-recognition region and to point out the crucial position of Arg469 as an amino-acid directly interacting with the sugar moiety. We cloned a flagged Hsc70 in a pCMV.SPORT6 vector and we showed that the mutation R469A decreased the GlcNAc-binding property of the chaperone of around 70%. This is the first work reporting the localization of the GlcNAc-binding domain of a member of the HSP70 family.

Glycosylated quantum dots for the selective labelling of Kluyveromyces bulgaricus and Saccharomyces cerevisiae yeast strains

Highly fluorescent CdTe quantum dots (QDs) stabilized by thioglycolic acid (TGA) were prepared by an aqueous solution approach and used as fluorescent labels in detecting yeast cells. Sugars (mannose, galactose or glucose) were adsorbed on CdTe@TGA QDs and the interaction of these nanoparticles with yeast cells was studied by fluorescence microscopy. Results obtained demonstrate that galactose and mannose functionalized QDs associate respectively with Kluyveromyces bulgaricus and Saccharomyces cerevisiae yeast strains due to saccharide/lectin specific recognition. Glucose-functionalized CdTe QDs, which are not recognized by cell lectins, preferentially localize in the bud scars of S. cerevisiae.

Polyvalent lactose-quantum dot conjugate for fluorescent labeling of live leukocytes

Oligosaccharides play crucial roles in many biorecognition processes by the so-called "cluster glycosidic effect". We here report a facile synthesis of lactose-CdSeS/ZnS quantum dot conjugate (Lac-QDs) by use of 1-thiol-beta-D-lactose via ligand exchange, which exhibits significantly high affinity and specificity to leukocytes in contrast to the monovalent lactose. Structural analyses indicate that there are about 132 lactosyl molecules assembled on single QDs and the hydrodynamic diameter is small, close to 8.2 nm. Further, Lac-QDs display good fluorescence and physicochemical stability in physiological conditions, as well as extremely low cytotoxicity. These properties facilitate the use of Lac-QDs in fluorescent labeling of live leukocytes.

Dysregulation of the nutrient/stress sensor O-GlcNAcylation is involved in the etiology of cardiovascular disorders, type-2 diabetes and Alzheimer's disease

O-GlcNAcylation is widespread within the cytosolic and nuclear compartments of cells. This post-translational modification is likely an indicator of good health since its intracellular level correlates with the availability of extracellular glucose. Apart from its status as a nutrient sensor, O-GlcNAcylation may also act as a stress sensor since it exerts its fundamental effects in response to stress. Several studies report that the cell quickly responds to an insult by elevating O-GlcNAcylation levels and by unmasking a newly described Hsp70-GlcNAc binding property. From a more practical point of view, it has been shown that O-GlcNAcylation impairments contribute to the etiology of cardiovascular diseases, type-2 diabetes and Alzheimer's disease (AD), three illnesses common in occidental societies. Many studies have demonstrated that O-GlcNAcylation operates as a powerful cardioprotector and that by raising O-GlcNAcylation levels, the organism more successfully resists trauma-hemorrhage and ischemia/reperfusion injury. Recent data have also shown that insulin resistance and, more broadly, type-2 diabetes can be controlled by O-GlcNAcylation of the insulin pathway and O-GlcNAcylation of the gluconeogenesis transcription factors FoxO1 and CRCT2. Lastly, the finding that AD may correspond to a type-3 diabetes offers new perspectives into the knowledge of the neuropathology and into the search for new therapeutic avenues.

Development of lipid particles targeted via sugar-lipid conjugates as novel nuclear gene delivery system

Efficient nuclear gene delivery is essential for successful gene therapy. This study developed a novel system that mimics the mechanism of nuclear entry of adenovirus (Ad) by means of a Multifunctional Envelope-type Nano Device (MEND). In this system, plasmid DNA (pDNA) was condensed with polycation, followed by encapsulation in a lipid membrane. To target MEND to the nuclear pore complex (NPC), sugar served as a NPC-mediated nuclear targeting device was modified on the surface of the lipid envelope. This was accomplished via synthesis of a sugar-cholesterol conjugate. After binding of the MEND to the NPC, the pDNA core was transferred into the nucleus in conjunction with a breakdown of the lipid envelope. Sugar-modified MEND showed higher transfection efficiency compared with unmodified MEND, in non-dividing and dividing cells. Confocal microscopy confirmed that nuclear transfer of pDNA was improved by sugar modification of MEND. Furthermore, destabilization of the lipid envelope significantly enhanced transfection activity: therefore, nuclear-delivery efficiency was closely related to lipid envelope stability. Moreover, quantitative evaluation of cellular uptake and nuclear transfer processes by real-time PCR confirmed that the surface sugars affected nuclear transfer, but not cellular uptake. In summary, a novel system for the nuclear delivery of pDNA was successfully developed by using a sugar-modified MEND and by optimizing the lipid envelope stability.