A Lichen Lectin Specifically Binds to the α-1,4-Polygalactoside Moiety of Urease Located in the Cell Wall of Homologous Algae

Abstract

A lectin from the lichen Evernia prunastri developing arginase activity (EC. 3.5.3.1) binds to the homologous algae that contain polygalactosilated urease (EC. 3.5.1.5) in their cell walls acting as a lectin ligand. The enzyme bound to its ligand shows to be inactive to hydrolyze of arginine. Hydrolysis of the galactoside moiety of urease in intact algae with alpha-1,4-galactosidase (EC. 3.2.1.22) releases high amount of D-galactose and impedes the binding of the lectin to the algal cell wall. However, the use of beta-,4-galactosidase (EC.3.2.1.23) releases low amounts of D-galactose from the algal cell wall and does not change the pattern of binding of the lectin to its ligand. The production of glycosilated urease is restricted to the season in which algal cells divide and this assures the recognition of new phycobiont produced after cell division by its fungal partner.

Fungal lectin of Peltigera canina induces chemotropism of compatible Nostoc cells by constriction-relaxation pulses of cyanobiont cytoskeleton

“…3 Some lectins from phycolichens are glycosylated arginases which bind to an algal cell wall receptor identified as an α-1,4-polygalactosylated urease. 4 The binding is enhanced by Ca 2+ and Mn 2+ , in a similar way to that described for legume lectins. 5 Since recognition must be achieved even for new algae produced inside the thallus after cell division, evolution of symbiotic relationships implies then the synchronization of cell division and lectin receptor production, probably as a consequence of the perception of environmental factors, such as light and temperature.…”

The cell recognition model in chlorolichens involving a fungal lectin binding to an algal ligand can be extended to cyanolichens

“…The universality of a unique receptor, a polygalactosylated urease, with different degrees of affinity for the ligand – high affinity for homologous and low affinity for heterologous arginases (Legaz et al. 2004; Sacristán et al. 2006a) – as well as the existence of other receptors for different glycoproteins (Marx & Peveling 1983; Fontaniella et al.…”

“…However, lichen phenolics are not involved in the recognition process (Millanes & Vicente 2003), in contrast to other plant symbioses, such as mycorrhizal or Rhizobium –legume associations (Doyle 1998). Some lectins from chlorolichens have been characterised as glycosylated arginases, which bind to an algal cell wall receptor identified as an α‐1,4‐polygalactosylated urease (Sacristán et al. 2006a).…”

Direct and cross-recognition of lichenized Trebouxia Puymaly (Chlorophyta, Trebouxiophyceae) and Nostoc Vaucher ex Bornet (Cyanobacteria, Cyanophyceae) by their homologous and heterologous fungal lectins

“…A major ligand of these lectins is a galactosylated urease, similar to that found in chlorolichens (Díaz et al 2009;Sacristán et al 2006;Vivas et al 2010). This urease, secreted from lichen thalli, can be used for rapid and efficient purification of the lectin by affinity chromatography.…”