Fungal Galectins, Sequence and Specificity of Two Isolectins from Coprinus cinereus

Abstract

Galectins are members of a genetically related family of ␤-galactoside-binding lectins. At least eight distinct mammalian galectins have been identified. More distantly related, but still conserving amino acid residues critical for carbohydrate-binding, are galectins in chicken, 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 formation which are 83% identical to each other in amino acid sequence and conserve all key residues shared by members of the galectin family. Unlike most galectins, these have no N-terminal post-translational modification and no cysteine residues. We expressed one of these as a recombinant protein and studied its carbohydrate-binding specificity using a novel nonradioactive assay. Binding specificity has been well studied for a number of other galectins, and like many of these, the recombinant C. cinereus galectin shows particular affinity for blood group A structures. These results demonstrate not only that the galectin gene family is evolutionarily much older than previously realized but also that fine specificity for complex saccharide structures has been conserved. Such conservation implies that galectins evolved to perform very basic cellular functions, presumably by interaction with glycoconjugates bearing complex lactoside carbohydrates resembling blood group A.Galectins are animal lectins that are related in amino acid sequence and specifically bind to ␤-galactoside carbohydrates such as lactose (1). Members of this gene family all include a conserved carbohydrate-binding domain but vary in inclusion of other domains and in tissue expression patterns. More distantly related, but conserving critical amino acid residues involved in carbohydrate-binding, are galectins in chicken, eel, frog, nematode, and sponge (2).Although galectins have been studied for 20 years now, physiological functions for these proteins have not yet been clearly established. Their affinity for oligosaccharides found on glycoconjugates on cell surfaces or in extracellular matrix has suggested that galectins function extracellularly by binding to such ligands. Indeed, certain galectins have particular affinity for specific glycoprotein ligands, such as polylactosamine chains on laminin (1, 3). When added to cells or overexpressed after transfection, galectins can have major effects on cell adhesion, proliferation, apoptosis, metastasis, and immune function (1-6). However, evidence has also been presented for intracellular functions of galectins, for instance in message splicing (7) or as nuclear proteins (8). Therefore, efforts are being directed at exploring the evolutionary origin of galectins in the hope that their functions will be easier to define in simple model organisms.Here we report that a species of fungus, the inky cap mushroom, Coprinus cinereus, expresses two lectins related in sequence and carbohydrate-binding specificity to other galectins. T...

Entomotoxic and nematotoxic lectins and protease inhibitors from fungal fruiting bodies

“…The genome of the model mushroom Coprinopsis cinerea contains a tandem gene array encoding two highly homologous galectins: CGL1 and CGL2 (Cooper et al 1997) (Table 1). In addition to these two proteins, the C. cinerea genome codes for a homologous, galectin-like protein, CGL3, that binds LacdiNAc and chitobiose but not β-galactosides (Walti et al 2008).…”

“…Besides these proteins from C. cinerea, galectins from two different Agrocybe species: ACG from Agrocybe cylindracea and AAG from Agrocybe aegerita, have been characterized (Yagi et al 2001;Yang et al 2009) (Table 1). The latter two share 88 % sequence identity Butschi et al 2010;Cooper et al 1997;Titz et al 2009;Walser et al 2004;Yan et al 2012) Gal-β1,4-GlcNAc Gal-β1,4-Glc na nd (Luan et al 2010;Yang et al 2009;Yang et al 2005a;Yang et al 2005b;Yang et al 2005c) ACG Agrocybe cylindracea 160 aa…”

Galectin-3 Induces Death of Candida Species Expressing Specific β-1,2-Linked Mannans

“…Recently, it has become apparent that the galectin family of lectins can also participate in the innate immune defense against pathogens (12). Galectins are present in all multicellular organisms, including worms, sponges, multicellular fungi, and insects (13)(14)(15)(16)(17)(18)(19). Galectins are PRRs in several types of organisms, and many mammalian pathogens express saccharide structures that are recognized by galectins.…”

Molecular analysis of Physarum haemagglutinin l: lack of a signal sequence, sulphur amino acids and post-translational modifications

“…Mushroom lectins in Flammulina uelutipes (Yatohgo et al, 1988) and Coprinus cinereus (Cooper et al, 1997) are developmentally regulated with high levels of expression in fruiting bodies and low levels of expression in vegetative mycelia, suggesting that these lectins may function in fruiting body formation. In P. polycephalum, however, it is unlikely that haemagglutinin I plays a role in the differentiation of plasmodia because acceleration of haemagglutinin synthesis was not always observed during macrocyst formation and fruiting body formation (Morita et al, 1995).…”