Broad-Spectrum Legionaminic Acid-Specific Antibodies in Pooled Human IgGs Revealed by Glycan Microarrays with Chemoenzymatically Synthesized Nonulosonosides.

The presence and the level of antibodies in human sera against bacterial glycans are indications of prior encounters with similar antigens and/or the bacteria that express them by the immune system. An increasing number of pathogenic bacteria that cause human diseases have been shown to express polysaccharides containing a bacterial nonulosonic acid called 5,7-di--acetyllegionaminic acid (Leg5,7Ac). To investigate the immune recognition of Leg5,7Ac, which is critical for the fight against bacterial infections, a highly effective chemoenzymatic synthon strategy was applied to construct a library of α2-3/6-linked Leg5,7Ac-glycans via their diazido-derivatives (Leg5,7diN-glycans) formed by efficient one-pot three-enzyme (OP3E) synthetic systems from a diazido-derivative of a six-carbon monosaccharide precursor.

Sialosides Containing 7--Acetyl Sialic Acid Are Selective Substrates for Neuraminidases from Influenza A Viruses.

Sialidases or neuraminidases are sialic-acid-cleaving enzymes that are expressed by a broad spectrum of organisms, including pathogens. In nature, sialic acids are monosaccharides with diverse structural variations, but the lack of novel probes has made it difficult to determine how sialic acid modifications impact the recognition by sialidases. Here, we used a chemoenzymatic synthon strategy to generate a set of α2-3- and α2-6-linked sialoside probes that contain 7--acetyl or 7,9-di--acetyl sialic acid as structure mimics for those containing the less stable naturally occurring 7--acetyl- or 7,9-di--acetyl modifications.

One-pot multienzyme (OPME) chemoenzymatic synthesis of brain ganglioside glycans with human ST3GAL II expressed in .

A human sialyltransferase ST3GAL II (hST3GAL II) was successfully expressed in as an active soluble fusion protein with an N-terminal maltose-binding protein (MBP) and a C-terminal hexa-histidine tag. It was used as an efficient catalyst in a one-pot multienzyme (OPME) sialylation system for high-yield production of the glycans of ganglioside GM1b and highly sialylated brain gangliosides GD1a and GT1b. Further sialylation of GM1b and GD1a glycans using a bacterial α2-8-sialyltransferase in another OPME sialylation reaction led to the formation of the glycans of GD1c and brain ganglioside GT1a, respectively.

Chemoenzymatic Synthesis of Sialosides Containing 7-- or 7,9-Di--acetyl Sialic Acid as Stable -Acetyl Analogues for Probing Sialic Acid-Binding Proteins.

A novel chemoenzymatic synthon strategy has been developed to construct a comprehensive library of α2-3- and α2-6-linked sialosides containing 7-- or 7,9-di--acetyl sialic acid, the stable analogue of naturally occurring 7--acetyl- or 7,9-di--acetyl-sialic acid. Diazido and triazido-mannose derivatives that were readily synthesized chemically from inexpensive galactose were shown to be effective chemoenzymatic synthons. Together with bacterial sialoside biosynthetic enzymes with remarkable substrate promiscuity, they were successfully used in one-pot multienzyme (OPME) sialylation systems for highly efficient synthesis of sialosides containing multiple azido groups.

Synthesis of -Glycolylneuraminic Acid (Neu5Gc) and Its Glycosides.

Sialic acids constitute a family of negatively charged structurally diverse monosaccharides that are commonly presented on the termini of glycans in higher animals and some microorganisms. In addition to -acetylneuraminic acid (Neu5Ac), -glycolyl neuraminic acid (Neu5Gc) is among the most common sialic acid forms in nature. Nevertheless, unlike most animals, human cells loss the ability to synthesize Neu5Gc although Neu5Gc-containing glycoconjugates have been found on human cancer cells and in various human tissues due to dietary incorporation of Neu5Gc.