Substitutions in the N-glycan core as regulators of biorecognition: the case of core-fucose and bisecting GlcNAc moieties.
Core fucosylation and the bisecting N-acetylglucosamine residue are prominent natural substitutions of the N-glycan core. To address the issue of whether these two substituents can modulate ligand properties of complex-type biantennary N-glycans, we performed chemoenzymatic synthesis of the respective galactosylated and alpha2,3/6-sialylated N-glycans. Neoglycoproteins were then produced to determine these glycans' reactivities with sugar receptors in solid-phase assays and with tumor cells in vitro as well as their in vivo biodistribution profiles in mice. Slight protein-type-dependent changes were noted in lectin binding, including adhesion/growth-regulatory galectins as study objects, when the data were related to properties of N-glycans without or with only one core substituent. Monitoring binding in vitro revealed cell-type-dependent changes. They delimited the ligand activity of this glycan type from that of chains with un- and monosubstituted cores. A markedly prolonged serum half-life was conferred to the neoglycoprotein by the galactose-terminated N-glycan, which together with increased organ retention of all three neoglycoproteins underscores the conspicuous relevance for glycoengineering of pharmaproteins. The predominant presentation of the two branches in the disubstituted N-glycan as extended (alpha1,3-antenna) and backfolded (alpha1,6-antenna) forms, revealed by molecular dynamics simulations, can underlie the measured characteristics. These results obtained by a combined strategy further support the concept of viewing N-glycan core substitutions as non-random additions which exert a modulatory role on ligand properties. Moreover, our data inspire us to devise new, non-natural modifications to realize the full potential of glycoengineering for diagnostic and therapeutic purposes.
André
Sabine
S
Institute of Physiological Chemistry, Faculty of Veterinary Medicine, Ludwig-Maximilians-University Munich, Veterinärstrasse 13, D-80539 Munich, Germany. Sabine.Andre@lmu.de
Kozár
Tibor
T
Schuberth
Ralf
R
Unverzagt
Carlo
C
Kojima
Shuji
S
Gabius
Hans-Joachim
HJ
D000117:Acetylglucosamine; D001665:Binding Sites; D002236:Carbohydrate Conformation; D002240:Carbohydrate Sequence; D005643:Fucose; D008024:Ligands; D009682:Magnetic Resonance Spectroscopy; D008969:Molecular Sequence Data; D011134:Polysaccharides / Q000737:chemistry*; D012794:Sialic Acids
D008024:Ligands; D011134:Polysaccharides; D012794:Sialic Acids; D005643:Fucose; D000117:Acetylglucosamine