A novel lectin has been isolated from the fruiting bodies of the common edible mushroom Boletus edulis (king bolete, penny bun, porcino or cep) by affinity chromatography on a chitin column. We propose for the lectin the name BEL (B. edulis lectin). BEL inhibits selectively the proliferation of several malignant cell lines and binds the neoplastic cell-specific T-antigen disaccharide, Galβ1-3GalNAc. The lectin was structurally characterized: the molecule is a homotetramer and the 142-amino acid sequence of the chains was determined. The protein belongs to the saline-soluble family of mushroom fruiting body-specific lectins. BEL was also crystallized and its three-dimensional structure was determined by X-ray diffraction to 1.15 A resolution. The structure is similar to that of Agaricus bisporus lectin. Using the appropriate co-crystals, the interactions of BEL with specific mono- and disaccharides were also studied by X-ray diffraction. The six structures of carbohydrate complexes reported here provide details of the interactions of the ligands with the lectin and shed light on the selectivity of the two distinct binding sites present in each protomer.

Structure of a lectin with antitumoral properties in king bolete (Boletus edulis) mushrooms.

A novel lectin was purified from the fruiting bodies of king bolete mushrooms (Boletus edulis, also called porcino, cep or penny bun). The lectin was structurally characterized i.e its amino acid sequence and three-dimensional structure were determined. The new protein is a homodimer and each protomer folds as β-trefoil domain and therefore we propose the name Boletus edulis lectin (BEL) β-trefoil to distinguish it from the other lectin that has been described in these mushrooms. The lectin has potent anti-proliferative effects on human cancer cells, which confers to it an interesting therapeutic potential as an antineoplastic agent. Several crystal forms of the apoprotein and of complexes with different carbohydrates were studied by X-ray diffraction. The structure of the apoprotein was solved at 1.12 A resolution. The interaction of the lectin with lactose, galactose, N-acetylgalactosamine and T-antigen disaccharide, Galβ1-3GalNAc, was examined in detail. All the three potential binding sites present in the β-trefoil fold are occupied in at least one crystal form and are described in detail in this paper. No important conformational changes are observed in the lectin when comparing its co-crystals with carbohydrates with those of the ligand-free protein.

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BEL β-trefoil: A novel lectin with antineoplastic properties in king bolete (Boletus edulis) mushrooms

The epididymis of lizards elaborates voluminous secretory granules made of a central core and a peripheral vacuole which in the species Lacerta vivipara contain respectively an insoluble protein (protein H) and a soluble protein (protein L). After their discharge these secretions mix with spermatozoa. In order to detect the presence of carbohydrates in these secretions, lectins isolated from Canavalia ensiformis (con A) and from eleven other plants (lentil, soja, pea, gorse and several mushrooms), conjugated to fluorescein isothiocyanate, have been utilized in light-microscopic histochemical investigations of frozen sections from Lacerta vivipara epididymis. Whereas lectins having affinity for L-fucose, lactose, D-galactose and N-acetyl-D-galactosamine bound to central cores, lectins having affinity to D-glucose, N-acetylglucosamine and chitobiose bound to the peripheral vacuole. D-mannose or D-glucose seem to be present both in central cores and in peripheral vacuoles.

Histochemical study of epididymal secretions in the lizard, Lacerta vivipara. Localization of lectin-binding sites.

bolete (Boletus edulis) mushrooms

Stromata prepared with human or animal red blood cells are suspended in acrylamide solution. Gel as prepared for electrophoresis is dispersed, before use, and can be used in chromatographic columns for the retention of agglutinins. Lectins, e.g., where first absorbed and then eluted with solution of inhibitory sugar or with acid buffer. Some applications are mentioned.

L Genaud

Papers

Erythrocyte stroma included in polyacrylamide gel. Applications to affinity chromatography

[Comparative study by quantitative hemagglutination, of the reaction between sugars and lectins in Canavalia ensiformis L. and Pisum sativum L].