1eis
UDA UNCOMPLEXED FORM. CRYSTAL STRUCTURE OF URTICA DIOICA AGGLUTININ, A SUPERANTIGEN PRESENTED BY MHC MOLECULES OF CLASS I AND CLASS II
|
OverviewOverview
BACKGROUND: Urtica dioica agglutinin (UDA), a monomeric lectin extracted, from stinging nettle rhizomes, is specific for saccharides containing, N-acetylglucosamine (GlcNAc). The lectin behaves as a superantigen for, murine T cells, inducing the exclusive proliferation of Vbeta8.3(+), lymphocytes. UDA is unique among known T cell superantigens because it can, be presented by major histocompatibility complex (MHC) molecules of both, class I and II. RESULTS: The crystal structure of UDA has been determined, in the ligand-free state, and in complex with tri-acetylchitotriose and, tetra-acetylchitotetraose at 1.66 A, 1.90 A and 1.40 A resolution, respectively. UDA comprises two hevein-like domains, each with a, saccharide-binding site. A serine and three aromatic residues at each site, form the principal contacts with the ligand. The N-terminal domain binding, site can centre on any residue of a chito-oligosaccharide, whereas that of, the C-terminal domain is specific for residues at the nonreducing terminus, of the ligand. We have shown previously that oligomers of GlcNAc inhibit, the superantigenic activity of UDA and that the lectin binds to glycans on, the MHC molecule. We show that UDA also binds to glycans on the T cell, receptor (TCR). CONCLUSIONS: The presence of two saccharide-binding sites, observed in the structure of UDA suggests that its superantigenic, properties arise from the simultaneous fixation of glycans on the TCR and, MHC molecules of the T cell and antigen-presenting cell, respectively. The, well defined spacing between the two binding sites of UDA is probably a, key factor in determining the specificity for Vbeta8.3(+) lymphocytes.
About this StructureAbout this Structure
1EIS is a Single protein structure of sequence from Urtica dioica. Full crystallographic information is available from OCA.
ReferenceReference
Crystal structure of Urtica dioica agglutinin, a superantigen presented by MHC molecules of class I and class II., Saul FA, Rovira P, Boulot G, Damme EJ, Peumans WJ, Truffa-Bachi P, Bentley GA, Structure. 2000 Jun 15;8(6):593-603. PMID:10873861
Page seeded by OCA on Sat Nov 24 22:21:41 2007