Lectins are carbohydrate-binding proteins that are neither enzymes nor antibodies. These proteins have become attractive tools owing to their distinct carbohydrate binding specificities and their potential role in, e.g. blood group typing. The largest and best-characterized lectin family is the legume lectin family. Because of the wide variety of carbohydrate specificities covered using a highly conserved scaffold, legume lectins are ideally suited as a model system to study the structural basis of protein-carbohydrate recognition.
Topology of ECL (complex with lactose). ECL residues that differ from ECorL are shown explicity. In addition, Val 92, the interaction partner of residues 111 and 125, is highlighted in orange.
About the project
We have chosen the two highly homologous legume lectins from E. cristagalli (ECL) and E. corallodendron (ECorL) as initial study objects. To this end, we have recently solved the crystal structure of ECL in complex with two different carbohydrate ligands at high resolution (Svensson et al., 2002). We are currently undertaking a detailed comparative analysis of ECL and ECorL, based on a variety of different methods including X-ray crystallography.
Recently,we have directed our interest towards mushroom lectins. Many mushroom species are toxic and a significant number of mushrooms possess tonic and medical attributes. Among the numerous compounds with important pharmacological properties that have been isolated from mushrooms are several lectins.
The first mushroom lectin we have investigated is the Marasmius oreades agglutinin (MOA) (Grahn et al., 2007 and 2009), which recognizes blood group B antigens. The MOA structure is dimeric, with two distinct domains per protomer: the N-terminal lectin module adopts a ricinB/β-trefoil fold and contains three putative carbohydrate binding sites, while the C-terminal domain serves as dimerization interface. This latter domain, which has an unknown function, reveals a novel fold with intriguing conservation of an active site cleft. A number of indications suggest that MOA may have an enzymatic function in addition to the sugar-binding properties. Interestingly, the carbohydrate specificity of MOA resembles that of some bacterial toxins, which induce Hemolytic-Uremic Syndrome (HUS)/Thrombotic Thrombocytopenic Purpura (TTP), a severe human disease that can lead to thrombosis, kidney failure and cortical necrosis. Experiments have demonstrated that MOA can induce damage of the kidney glomerular epithelial cells in mice, which resembles the pathological patterns of HUS/TTP in humans (Warner et al., 2004). It is intriguing to speculate that the potential catalytic activity of MOA may be responsible for these toxic effects.
MOA structure showing the three potential sugar-binding sites a, b and g.
The lectin projects involve the close collaboration with the research groups of Nathan Sharon, Weizmann Institute, Rehovot, Israel (Erythrina lectins) and Irwin Goldstein, University of Michigan, Ann Arbor, Michigan, U.S.A. (mushroom lectins).
Grahn et al. (2009), J. Mol. Biol. 390, 457-466.
Grahn et al. (2007), J. Mol. Biol. 369, 710-721.
U. Krengel & A. Imberty (2007), Crystallography and lectin structure database, In: Lectins: Analytical technologies (C. Nilsson, Ed.), Elsevier, pp.15-50.
Svensson et al. (2002), J. Mol. Biol. 321, 69-83.
Warner et al. (2004), Exp. Mol. Pathol. 77, 77-84.