Abstract
BACKGROUND: Lectins are carbohydrate-binding proteins which potentially bind to cell surface glycoconjugates. They are found in various organisms including fungi. A lectin from the mushroom Xerocomus chrysenteron (XCL) has been isolated recently. It shows insecticidal activity and has antiproliferative properties. RESULTS: As the monosaccharide binding specificity is an important determinant of lectin function, we determined the affinity of XCL for the galactose moiety. Isothermal titration calorimetry studies revealed a dissociation constant Kd of 5.2 microM for the XCL:N-acetylgalactosamine interaction at 27 degrees C. Higher affinities were observed at lower temperatures and higher osmotic pressures. The dissociation constant was five hundred times higher for the disaccharide beta-D-Gal(1-3)-D-GalNAc, Thomsen-Friedenreich (TF) antigen (Kd of 0.94 microM). By using fetuin and asialofetuin in interaction with the XCL, we revealed its ability to recognize the Thomsen-Friedenreich motif on glycoproteins. CONCLUSION: The XCL antiproliferative effect and the TF antigen specificity presented in this work suggest that XCL and ABL may have similar binding mechanisms. The recent structure determination of these two proteins lead us to analyse these interactions in the light of our thermodynamic data. The understanding of this type of interaction may be a useful tool for the regulation of cell proliferation.