FUNGAL GALECTINS, SEQUENCE AND SPECIFICITY OF 2 ISOLECTINS FROM COPRINUS-CINEREUS

Galectins are members of a genetically related family of beta-galactos ide-binding lectins. At least eight distinct mammalian galectins have been identified. More distantly related, but still conserving amino ac id residues critical for carbohydrate-binding, are galectins in chicke n, eel, frog, nematode, and sponge. Here we report that galectins are also expressed in a species of fungus, the inky cap mushroom, Coprinus cinereus. Two dimeric galectins are expressed during fruiting body fo rmation which are 83% identical to each other in amino acid sequence a nd conserve all key residues shared by members of the galectin family. Unlike most galectins, these have no N-terminal post-translational mo dification and no cysteine residues. We expressed one of these as a re combinant protein and studied its carbohydrate-binding specificity usi ng a novel nonradioactive assay. Binding specificity has been well stu died for a number of other galectins, and like many of these, the reco mbinant C. cinereus galectin shows particular affinity for blood group A structures. These results demonstrate not only that the galectin ge ne family is evolutionarily much older than previously realized but al so that fine specificity for complex saccharide structures has been co nserved. Such conservation implies that galectins evolved to perform v ery basic cellular functions, presumably by interaction with glycoconj ugates bearing complex lactoside carbohydrates resembling blood group A.