Sialic acid mediated mechanical activation of ß2 adrenergic receptors by bacterial pili.

Meningococcus utilizes ß-arrestin selective activation of endothelial cell ß2 adrenergic receptor (ß2AR) to cause meningitis in humans. Molecular mechanisms of receptor activation by the pathogen and of its species selectivity remained elusive. We report that ß2AR activation requires two asparagine-branched glycan chains with terminally exposed N-acetyl-neuraminic acid (sialic acid, Neu5Ac) residues located at a specific distance in its N-terminus, while being independent of surrounding amino-acid residues. Meningococcus triggers receptor signaling by exerting direct and hemodynamic-promoted traction forces on ß2AR glycans. Similar activation is recapitulated with beads coated with Neu5Ac-binding lectins, submitted to mechanical stimulation. This previously unknown glycan-dependent mode of allosteric mechanical activation of a G protein-coupled receptor contributes to meningococcal species selectivity, since Neu5Ac is only abundant in humans due to the loss of CMAH, the enzyme converting Neu5Ac into N-glycolyl-neuraminic acid in other mammals. It represents an additional mechanism of evolutionary adaptation of a pathogen to its host.

Changes in canine serum N-glycosylation as a result of infection with the heartworm parasite Dirofilaria immitis.

Filariases are diseases caused by infection with filarial nematodes and transmitted by insect vectors. The filarial roundworm Dirofilaria immitis causes heartworm disease in dogs and other carnivores. D. immitis is closely related to Onchocerca volvulus, Wuchereria bancrofti and Brugia malayi, which cause onchocerciasis (river blindness) and lymphatic filariasis (elephantiasis) in humans and are neglected tropical diseases. Serum N-glycosylation is very sensitive to both pathological infections and changes in mammalian biology due to normal aging or lifestyle choices. Here, we report significant changes in the serum N-glycosylation profiles of dogs infected with D. immitis. Our data derive from analysis of serum from dogs with established patent infections and from a longitudinal infection study. Overall, galactosylation and core fucosylation increase, while sialylation decreases in infected dog sera. We also identify individual glycan structures that change significantly in their relative abundance during infection. Notably, the abundance of the most dominant N-glycan in canine serum (biantennary, disialylated A2G2S2) decreases by over 10 percentage points during the first 6 months of infection in each dog analyzed. This is the first longitudinal study linking changes in mammalian serum N-glycome to progression of a parasitic infection.

Glycosylation profiling of dog serum reveals differences compared to human serum.

Glycosylation is the most common post-translational modification of serum proteins, and changes in the type and abundance of glycans in human serum have been correlated with a growing number of human diseases. While the glycosylation pattern of human serum is well studied, little is known about the profiles of other mammalian species. Here, we report detailed glycosylation profiling of canine serum by hydrophilic interaction chromatography-ultraperformance liquid chromatography (HILIC-UPLC) and mass spectrometry. The domestic dog (Canis familiaris) is a widely used model organism and of considerable interest for a large veterinary community. We found significant differences in the serum N-glycosylation profile of dogs compared to that of humans, such as a lower abundance of galactosylated and sialylated glycans. We also compare the N-glycan profile of canine serum to that of canine IgG - the most abundant serum glycoprotein. Our data will serve as a baseline reference for future studies when performing serum analyses of various health and disease states in dogs.

An engineered high affinity Fbs1 carbohydrate binding protein for selective capture of N-glycans and N-glycopeptides.

A method for selective and comprehensive enrichment of N-linked glycopeptides was developed to facilitate detection of micro-heterogeneity of N-glycosylation. The method takes advantage of the inherent properties of Fbs1, which functions within the ubiquitin-mediated degradation system to recognize the common core pentasaccharide motif (Man3GlcNAc2) of N-linked glycoproteins. We show that Fbs1 is able to bind diverse types of N-linked glycomolecules; however, wild-type Fbs1 preferentially binds high-mannose-containing glycans. We identified Fbs1 variants through mutagenesis and plasmid display selection, which possess higher affinity and improved recovery of complex N-glycomolecules. In particular, we demonstrate that the Fbs1 GYR variant may be employed for substantially unbiased enrichment of N-linked glycopeptides from human serum. Most importantly, this highly efficient N-glycopeptide enrichment method enables the simultaneous determination of N-glycan composition and N-glycosites with a deeper coverage (compared to lectin enrichment) and improves large-scale N-glycoproteomics studies due to greatly reduced sample complexity.

Profiling of core fucosylated N-glycans using a novel bacterial lectin that specifically recognizes α1,6 fucosylated chitobiose.

A novel fucose-binding lectin (SL2-1) from the bacterium Streptomyces rapamycinicus was identified by analysis of metagenomic DNA sequences. SL2-1 belongs to a new group of bacterial fucose-specific lectins that have no similarity to known bacterial fucose-binding proteins, but are related to certain eukaryotic fucose-binding lectins. The 17 kDa protein was expressed recombinantly in E. coli and purified by affinity chromatography. Glycan microarray analysis with fluorescently labeled recombinant SL2-1 demonstrated its ability to bind to core α1-6 fucosylated N-glycans, but not to core α1-3 fucosylated N-glycans, or other α1-2, α1-3 and α1-4 fucosylated oligosaccharides. The minimal high affinity binding epitope of SL2-1 was α1-6 fucosylated di-n-acetylchitobiose. The recombinant lectin was efficient in detection of N-glycan core fucosylation using lectin blotting and lectin ELISA assays. Finally, a workflow using SL2-1 for selective and quantitative profiling of core fucosylated N-glycans using UPLC-HILIC-FLR analysis was established. The approach was validated for selective capture and analysis of core fucosylated N-glycans present in complex glycan mixtures derived from mammalian serum IgG.

Ultrahigh throughput, ultrafiltration-based n-glycomics platform for ultraperformance liquid chromatography (ULTRA(3)).

Accurate, reproducible, and fast quantification of N-glycans is crucial not only for the development and quality control of modern glycosylated biopharmaceuticals, but also in clinical biomarker discovery. Several methods exist for fluorescent labeling of N-glycans and subsequent chromatographic separation and quantification. However, the methods can be complex, lengthy, and expensive. Here we report an automated ultrafiltration-based N-glycoanalytical workflow combined with a glycan labeling strategy that is based on the reaction of glycosylamines with fluorescent carbamate. The entire protocol is quick, simple, and cost-effective and requires less than 1 µg of protein per sample. As many as 768 affinity purified IgG glycoprotein samples can be prepared in a single run with a liquid handling platform.

Formation of luminescent terbium(III) self-assemblies from pyridyl bis-amidothioureas based ligands in MeOH and in water-DMSO solutions and their use in anion sensing application.

The self-assembly between the amidothiourea ligands 1 and 2 and Tb(III) gave rise to the formation of 1:1 and 3:1 (ligand-Tb) supramolecular architectures that were shown to be luminescent in both MeOH and in water-DMSO solutions; preliminary investigations in the latter system also showed that their emission was modulated upon interacting with anions such as acetate and phosphate due to host-guest formation.

Recognition and sensing of biologically relevant anions in alcohol and mixed alcohol-aqueous solutions using charge neutral cleft-like glycol-derived pyridyl-amidothiourea receptors.

In this paper, the synthesis and the spectroscopic investigation of new colorimetric receptors for anions 3-6, possessing a glycol chain at the 4-position of the pyridyl ring, and 1 and 2, which lack such a chain, and the X-ray crystal structure of 2 is presented. Structures 3-6 are able to bind to anions in competitive media, such as alcohol or in a mixture of methanol and water, where the anion recognition gives rise to changes in the absorption spectra, which is red-shifted, in 1:1 or 1:2 (sensor/anion) stoichiometry. The anion recognition for 1 and 2 was also investigated in organic solvents and in a 4:1 mixture of DMSO/H(2)O. The binding of 1 to anions such as acetate, phosphate, and fluoride was also evaluated using (1)H NMR in DMSO-d(6).

Colorimetric and fluorescent anion sensors: an overview of recent developments in the use of 1,8-naphthalimide-based chemosensors.

This critical review focuses on the development of anion sensors, being either fluorescent and/or colorimetric, based on the use of the 1,8-naphthalimide structure; a highly versatile building unit that absorbs and emits at long wavelengths. The review commences with a short description of the most commonly used design principles employed in chemosensors, followed by a discussion on the photophysical properties of the 4-amino-1,8-naphthalimide structure which has been most commonly employed in both cation and anion sensing to date. This is followed by a review of the current state of the art in naphthalimide-based anion sensing, where systems using ureas, thioureas and amides as hydrogen-bonding receptors, as well as charged receptors have been used for anion sensing in both organic and aqueous solutions, or within various polymeric networks, such as hydrogels. The review concludes with some current and future perspectives including the use of the naphthalimides for sensing small biomolecules, such as amino acids, as well as probes for incorporation and binding to proteins; and for the recognition/sensing of polyanions such as DNA, and their potential use as novel therapeutic and diagnostic agents (95 references).

Colorimetric sensing of anions in aqueous solution using a charge neutral, cleft-like, amidothiourea receptor: tilting the balance between hydrogen bonding and deprotonation in anion recognition.

The design, synthesis and physical evaluation of 1, a visible colorimetric 'naked eye' pyridyl based bis-amidothiourea sensor for anions, is described. This charge neutral sensor gives rise to significant changes in the absorption spectra upon interactions with several important biological anions such as AMP and ADP in 4:1 DMSO-H(2)O solution, while ATP was not detected. These colorimetric changes are due to the formation, or the combination of hydrogen bonding complexes and/or deprotonation between these anions and 1.