Journal
GLYCOBIOLOGY
Volume 20, Issue 12, Pages 1643-1653Publisher
OXFORD UNIV PRESS INC
DOI: 10.1093/glycob/cwq118
Keywords
glycan array; lectin subsites; Maclura pomifera agglutinin
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Funding
- National Institutes of Health, Bethesda, MD [GM079191]
- National Institute of General Medical Sciences of the NIH [GM62116]
- U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences [DE-AC02-98CH10886]
- Howard Hughes Medical Institute
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The Maclura pomifera agglutinin (MPA) recognizes the T-antigen disaccharide Gal beta 1,3GalNAc mainly through interaction of the a-GalNAc moiety with its primary site, but the interactions of the two flanking subsites A and B with aglycones and substituents other than Gal, respectively, are not well understood. We therefore characterized the specificity of MPA in more detail by glycan microarray analysis and determined the crystal structures of MPA without ligand and in complexes with Gal beta 1,3GalNAc and p-nitrophenyl a-GalNAc. In both sugar complexes, pairs of ligands created inter-tetramer hydrogen-bond bridging networks. While subsite A showed increased affinity for hydrophobic aglycones, it also accommodated several sugar substituents. Notably, a GalNAc-O-tripeptide, a Tn-antigen mimic, showed lower affinity than these compounds in surface plasmon resonance (SPR) experiments. The glycan array data that showed subsite B accepted compounds in which the O3 position of the GalNAc was substituted with various sugars other than Gal, but substitutions at O6 led to inactivity. Additions to the Gal moiety of the disaccharide also had only small effects on reactivity. These results are all compatible with the features seen in the crystal structures.
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