Bivalent Carbohydrate Binding Is Required for Biological Activity of Clitocybe nebularis Lectin (CNL), the N,N′-Diacetyllactosediamine (GalNAcβ1–4GlcNAc, LacdiNAc)-specific Lectin from Basidiomycete C. nebularis

Abstract

Background: Lectins are carbohydrate-binding proteins that exert their activity by binding to specific glycoreceptors. Results: Clitocybe nebularis lectin (CNL) showed biological activity, although its nonsugar-binding and monovalent mutants were inactive. Conclusion:The bivalent carbohydrate-binding property of CNL is essential for its activity. Significance: Understanding the interactions of lectins with glycans and elucidating their modes of action are necessary for their application in biomedicine.

Entomotoxic and nematotoxic lectins and protease inhibitors from fungal fruiting bodies

“…In addition to these canonical sites, the β-trefoil fold can also harbor noncanonical carbohydrate-binding sites (Schubert et al 2012) and, as in case of protease inhibitors, binding sites for proteases (Žurga et al 2015) (see below). The best characterized representatives of this family of mushroom lectins are Rhizoctonia solani agglutinin (RSA) and Sclerotinia sclerotiorum agglutinin (SSA) of the plant pathogens R. solani (basidiomycete) (Hamshou et al 2013) and S. sclerotiorum (ascomycete) (Sulzenbacher et al 2010), as well as CNL, CCL2, MpL, and BEL β-trefoil of the homobasidio(agarico)mycetes Clitocybe nebularis (Pohleven et al 2009;Pohleven et al 2012), C. cinerea (Schubert et al 2012), Macrolepiota procera (Žurga et al 2014), and Boletus edulis (Bovi et al 2013) (Table 1). These proteins show high sequence variability, as they share only 7 to 16 % sequence identity (25 to 35 % similarity), the exception being CNL, MpL, and RSA that are 23 to 26 % identical (30 to 40 % similar).…”

“…While galectins bind linear glycans in a groove parallel to the protein surface, β-trefoil-type lectins bind them in a perpendicular orientation, in which only the non-reducing end of the glycan interacts with the binding pocket. All these proteins assemble to homodimers but, interestingly, each protein uses a different interface for dimer formation (Bovi et al 2013;Pohleven et al 2012;Schubert et al 2012;Skamnaki et al 2013;Sulzenbacher et al 2010;Žurga et al 2014).…”

“…The mechanism of toxicity of these (and other) hololectins is not clear. The toxicity of CNL against C. elegans has been shown to depend on both glycan binding and dimer formation (Pohleven et al 2012). Recently, CCL2 was shown to bind to the nematode intestinal epithelium without being endocytosed (Stutz et al 2015).…”

Crystal Structures of a Plant Trypsin Inhibitor from Enterolobium contortisiliquum (EcTI) and of Its Complex with Bovine Trypsin

“…Such functions may include chlorophyll binding [3], taste modification (miraculin [4]), binding to cytokine receptors (IL-1β [5]), tight binding to ribosomes (ricin [6]) or carbohydrate binding, exemplified by the Clitocybe nebularis lectin, CNL [7]. Prominent among them are plant protease inhibitors of the Kunitz type, the first one isolated by Kunitz [8] from soybeans and named soybean trypsin inhibitor (STI).…”

Glycoconjugates in Host-Helminth Interactions

“…While this review section is devoted to mammalian responses to helminth infections, it is worth noting that other organisms have also developed a wide range of responses to helminth infections. For example, one lectin (CNL) from the mushroom Clitocybe nebularis (78) can bind to the LDN motif, and the recombinant form of the CNL can directly kill the hypersensitive C. elegans mutant strain pmk-1 (79). Other types of fungi, on which C. elegans feeds, express specific lectins that recognize the core galactose-fucose determinants (57).…”