Chemoenzymatische Synthesen von Sialyloligosacchariden mit immobilisierter Sialidase

Carbohydrate-Lectin Interactions: An Unexpected Contribution to Affinity

Uropathogenic E. coli exploit PapG-II adhesin for infecting host cells of the kidney; the expression of PapG-II at the tip of bacterial pili correlates with the onset of pyelonephritis in humans, a potentially life-threatening condition. It was envisaged that blocking PapG-II (and thus bacterial adhesion) would provide a viable therapeutic alternative to conventional antibiotic treatment. In our search for potent PapG-II antagonists, we observed an increase in affinity when tetrasaccharide 1, the natural ligand of PapG-II in human kidneys, was elongated to hexasaccharide 2, even though the additional Siaα(2-3)Gal extension is not in direct contact with the lectin. ITC studies suggest that the increased affinity results from partial desolvation of nonbinding regions of the hexasaccharide; this is ultimately responsible for perturbation of the outer hydration layers. Our results are in agreement with previous observations and suggest a general mechanism for modulating carbohydrate-protein interactions based on nonbinding regions of the ligand.

Regioselective transglycosylation in the synthesis of oligosaccharides: comparison of beta-galactosidases and sialidases of various origins

N-Acetyl-lactosamine(beta-D-Gal p-(1-->4)-D-Glc pNAc) was synthesized regioselectively with the aid of the transglycosylation activity of beta-galactosidase isolated from Diplococcus pneumoniae using p-nitrophenyl beta-D-galactopyranoside as the donor. Also, transglycosylation of the sialyl group in an alpha-(2-->8)-linked sialic acid dimer or p-nitrophenyl glycoside of sialic acid to N-acetyl-lactosamine was performed using sialidases of various origins. When sialidase from Clostridium perfringens, Arthrobacter ureafaciens, or Vibrio cholerae was used, alpha-(2-->6)-linked sialyl N-acetyl-lactosamine was obtained regioselectively. In contrast, when sialidase from newcastle disease virus was used, the alpha-(2-->3)-linked isomer was obtained regioselectively. The regioselectivity of the transglycosylation reaction using beta-galactosidase and sialidase was compared with hydrolysis specificity toward the same linkages.