A melibiose- and xylose-cospecific homodimeric lectin was isolated from fresh fruiting bodies of Boletus edulis. The lectin was isolated using a protocol that consisted of ion exchange chromatography on DEAE-cellulose, affinity chromatography on CM-cellulose and gel filtration by fast protein liquid chromatography on Superdex 75. It was a dimer made up of two 16.3 kDa subunits. The hemagglutinating activity of the lectin was stable up to 40 degrees C, and in the presence of NaOH or HCl solutions up to a concentration of 25 mM. The hemagglutinating activity of the lectin was unaffected in the presence of AlCl3 and FeCl3 at and above 2 mM. MgCl2, ZnCl2 and MnCl2 inhibited the lectin activity. The lectin stimulated the mitogenic response of mouse splenocytes attaining a maximum at 1 mu M, and inhibited human immunodeficiency virus-1 reverse transcriptase with an IC50 Of 14.3 mu M. It did not exhibit antifungal activity. (c) 2007 Published by Elsevier Ltd.