Synthesis of N-acetylmannosamine-6-phosphate derivatives to investigate the mechanism of N-acetylmannosamine-6-phosphate 2-epimerase.

The synthesis of analogues of natural enzyme substrates can be used to help deduce enzymatic mechanisms. N-Acetylmannosamine-6-phosphate 2-epimerase is an enzyme in the bacterial sialic acid catabolic pathway. To investigate whether the mechanism of this enzyme involves a re-protonation mechanism by the same neighbouring lysine that performed the deprotonation or a unique substrate-assisted proton displacement mechanism involving the substrate C5 hydroxyl, the syntheses of two analogues of the natural substrate, N-acetylmannosamine-6-phosphate, are described. In these novel analogues, the C5 hydroxyl has been replaced with a proton and a methyl ether respectively. As recently reported, Staphylococcus aureus N-acetylmannosamine-6-phosphate 2-epimerase was co-crystallized with these two compounds. The 5-deoxy variant bound to the enzyme active site in a different orientation to the natural substrate, while the 5-methoxy variant did not bind, adding to the evidence that this enzyme uses a substrate-assisted proton displacement mechanism. This mechanistic information may help in the design of potential antibacterial drug candidates.

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.

Size-optimized galactose-capped gold nanoparticles for the colorimetric detection of heat-labile enterotoxin at nanomolar concentrations.

The development of a galactose-capped gold nanoparticle-based colorimetric sensor for the detection of the lectin heat-labile enterotoxin is reported. Heat-labile enterotoxin is one of the pathogenic agents responsible for the intestinal disease called 'traveller's diarrhoea'. By means of specific interaction between galactose moieties attached to the surface of gold nanoparticles and receptors on the B-subunit of heat-labile enterotoxin (LTB), the gold nanoparticles reported here act as an efficient colorimetric sensor, which can detect the toxin at nanomolar concentrations. The effect of gold nanoparticle size on the detection sensitivity was investigated in detail. Amongst the various sizes of gold nanoparticles studied (2, 7, 12, and 20 nm), the 12 nm sized gold nanoparticles were found to be the most efficient, with a minimum heat-labile enterotoxin detection concentration of 100 nM. The red to purple colour change of the gold nanoparticle solution occurred within two minutes, indicating rapid toxin sensing.

Gold Nanoparticles Decorated with Sialic Acid Terminated Bi-antennary N-Glycans for the Detection of Influenza Virus at Nanomolar Concentrations.

Invited for this month's cover picture is the group of Professor Antony Fairbanks and his collaborators at the University of Canterbury and University of Otago. The cover shows the isolation of complex bi-antennary oligosaccharides from hens' eggs and their conjugation to gold nanoparticles. Gold nanoparticles carrying these sugars can then bind to specific receptors (hemagglutinin) on the surface of the influenza virus, causing particle aggregation, which changes their spectroscopic properties. Upon aggregation, they undergo a red-shift in their surface plasmon resonance, as illustrated by the bound particles shining in the cover image. These changes in spectroscopic properties are the basis of a detection system capable of detecting viral hemagglutinin at nanomolar concentrations, as well as the virus itself. For more details, see the Full Paper on p. 708 ff.Read the full text of the article at 10.1002/open.201500109.

Gold Nanoparticles Decorated with Sialic Acid Terminated Bi-antennary N-Glycans for the Detection of Influenza Virus at Nanomolar Concentrations.

Gold nanoparticles decorated with full-length sialic acid terminated complex bi-antennary N-glycans, synthesized with glycans isolated from egg yolk, were used as a sensor for the detection of both recombinant hemagglutinin (HA) and whole influenza A virus particles of the H1N1 subtype. Nanoparticle aggregation was induced by interaction between the sialic acid termini of the glycans attached to gold and the multivalent sialic acid binding sites of HA. Both dynamic light scattering (DLS) and UV/Vis spectroscopy demonstrated the efficiency of the sensor, which could detect viral HA at nanomolar concentrations and revealed a linear relationship between the extent of nanoparticle aggregation and the concentration of HA. UV/Vis studies also showed that these nanoparticles can selectively detect an influenza A virus strain that preferentially binds sialic acid terminated glycans with α(2→6) linkages over a strain that prefers glycans with terminal α(2→3)-linked sialic acids.