Structure of the Complex of Maclura pomiferaAgglutinin and the T-antigen Disaccharide, Galβ1,3GalNAc

Abstract

Maclura pomifera agglutinin is a tetrameric plant seed lectin with high affinity for the tumor-associated T-antigen disaccharide, Gal␤1,3GalNAc␣, and hence for many O-linked glycopeptide structures. Unlike members of most lectin families, it lacks both metal ions and Cys residues. The structure of its complex with Gal␤1,3GalNAc was determined to 2.2 Å by first using multiwavelength anomalous diffraction with a lead derivative of the native protein, and then using molecular replacement with the unrefined structure as a model to solve the structure of the complex. The subunits share the ␤-prism architecture and three-fold pseudo-symmetry of the related lectin jacalin, with the 21-residue ␤-chains in the center of the tetramer. Interactions with the GalNAc predominate in the binding of the disaccharide. It forms a network of H-bonds with only one side chain, from an Asp residue, the amino group of the Nterminal Gly of the ␣-chain, and peptide backbone atoms of two aromatic residues. The Gal moiety does not Hbond directly with residues in the same monomer, i.e. there is no true subsite for it, but there are interactions through two water molecules. In the crystal, it interacts with residues in the binding site of an adjacent tetramer. The minimum energy conformation expected for the disaccharide is retained, despite its mediating the tetramer-tetramer interactions in the crystal packing. The resulting lattice is comparable to those seen for complexes of other lectins with branched glycopeptides.

Maize β-Glucosidase-aggregating Factor Is a Polyspecific Jacalin-related Chimeric Lectin, and Its Lectin Domain Is Responsible for β-Glucosidase Aggregation

“…Gal binding and broader specificity of gJRLs is believed to be due to co-/posttranslational processing of their precursor polypeptide chain, which generates a larger ␣-chain and a smaller ␤-chain (27). The amino group of Gly at the newly created N terminus (␤-chain) has been shown to interact with O-4 of Gal and is believed to confer galactose-binding specificity to jacalin and MPA lectins (19,24). Astoul et al (44) proposed that the differ- Fig.…”

The Antineoplastic Lectin of the Common Edible Mushroom (Agaricus bisporus) Has Two Binding Sites, Each Specific for a Different Configuration at a Single Epimeric Hydroxyl

“…In particular, the carbonyl of Glu 36 is in contact with the nitrogen of Arg 38 of the other monomer and vice versa. Another important contact is established between the side chains of Arg 38 and Asp 35 of the other monomer. Overall, these interactions appear to be less extensive than those observed within the dimer in the asymmetric unit (Fig.…”

“…In addition to these hydrogen bonds between the two strands, another contact is established between the side chains of Glu 22 of one chain and Asn 25 of the other. Another contact is established between strand B of one monomer and strand C of the other sheet in the other monomer: the side chains of Arg 19 in one monomer and Asp 35 of the other monomer are in contact with each other. These contacts between monomers force the two Arg 23 residues into positions that are quite close to one another (and also very close to the non-crystallographic dyad), but the positive charges of the arginines are neutralized by those of the two Glu 36 of the same monomer.…”

Glycotope Structures and Intramolecular Affinity Factors of Plant Lectins for Tn/T Antigens

“…Moreover, the affinity towards T antigen is often enhanced by its clustering at the surface of tumor cells [39] (this holds also true for the Tn-antigen!!!). X-ray analysis of the corresponding lectin-T antigen-complexes demonstrated that the carbohydrate-binding site of the Maclura pomifera agglutinin (MPA) (PDB code 1JOT) [40] and jacalin from Artocarpus integrifolia (PDB code 1M26) [41], which both belong to the family Moraceae, accommodate the T antigen disaccharide in a similar way (Fig. 2D,E).…”