2sba
From Proteopedia
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SOYBEAN AGGLUTININ COMPLEXED WITH 2,6-PENTASACCHARIDE
Overview
Soybean agglutinin (SBA) (Glycine max), which is a tetrameric, GalNAc/Gal-specific lectin, has recently been reported to form unique, highly organized cross-linked complexes with a series of naturally, occurring and synthetic multiantennary carbohydrates with terminal GalNAc, or Gal residues [Gupta, D., Bhattacharyya, L., Fant, J., Macaluso, F., Sabesan, S., & Brewer, C. F. (1994) Biochemistry 33, 7495-7504]. In order, to elucidate the nature of these complexes, the X-ray crystallographic, structure of SBA cross-linked with a biantennary analog of the blood group, I carbohydrate antigen is reported. The structure reveals that lattice, formation is promoted uniquely by the bridging action of the bivalent, pentasaccharide (beta-LacNAc)2Gal-beta-R, where R is -O(CH2)5COOCH3 and, the beta-LacNAc moieties are linked to the 2 and 6 positions of the core, Gal. The structure of SBA complexed with the synthetic biantennary, pentasaccharide has thus been determined by molecular replacement, techniques and refined at 2.6 A resolution to an R value of 20.1%. The, crystals are hexagonal with a P6(4)22 space group, which differs, significantly from that of crystals of the free protein. In the structure, each monomeric asymmetric unit contains a Man9 oligomannose-type chain at, Asn 75, with only the first two GlcNAc residues visible. The overall, tertiary structure of the SBA subunit is similar to that of other legume, lectins as well as certain animal lectins. However, the dimer interface in, the SBA tetramer is unusual in that only one complete peptide chain is, sterically permitted, thus requiring juxtapositioning of one C-terminal, fragmented subunit together with an intact subunit. Association between, SBA tetramers involves binding of the terminal Gal residues of the, pentasaccharide at identical sites in each monomer, with the sugar, cross-linking to a symmetry-related neighbor molecule. The cross-linking, pentasaccharide is in a conformation that possesses a pseudo-2-fold axis, of symmetry which lies on a crystallographic 2-fold axis of symmetry of, the lattice. Hence, the symmetry properties of the bivalent, oligosaccharide as well as the lectin are structural determinants of the, lattice. The results are discussed in terms of multidimensional, carbohydrate-lectin cross-linked complexes, as well as the signal, transduction properties of multivalent lectins.
About this Structure
2SBA is a Single protein structure of sequence from Glycine max with MN and CA as ligands. This structure superseeds the now removed PDB entry 1SBA. Full crystallographic information is available from OCA.
Reference
X-ray crystal structure of the soybean agglutinin cross-linked with a biantennary analog of the blood group I carbohydrate antigen., Dessen A, Gupta D, Sabesan S, Brewer CF, Sacchettini JC, Biochemistry. 1995 Apr 18;34(15):4933-42. PMID:7711015
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