Hitting the Sweet Spot: Glycans as Targets of Fungal Defense Effector Proteins

Abstract

Organisms which rely solely on innate defense systems must combat a large number of antagonists with a comparatively low number of defense effector molecules. As one solution of this problem, these organisms have evolved effector molecules targeting epitopes that are conserved between different antagonists of a specific taxon or, if possible, even of different taxa. In order to restrict the activity of the defense effector molecules to physiologically relevant taxa, these target epitopes should, on the other hand, be taxon-specific and easily accessible. Glycans fulfill all these requirements and are therefore a preferred target of defense effector molecules, in particular defense proteins. Here, we review this defense strategy using the example of the defense system of multicellular (filamentous) fungi against microbial competitors and animal predators.

Functional studies of aegerolysin and MACPF‐like proteins in Aspergillus niger

“…mites and insect larvae). Many of the observed characteristics for aegerolysin proteins in A. niger resemble those described for secondary metabolites and lectins in fungi who act as defence molecules in organisms that produce them (Calvo et al ., ; Mylonakis et al ., ; Künzler, ; Sabotič et al ., ). Therefore, this leads us to believe that the main role(s) of aegerolysins in A. niger are linked to the defence/protection of the fungus during the sensitive period of its development, rather than to growth and development of the fungus.…”

Complex multicellularity in fungi: evolutionary convergence, single origin, or both?

“…Fruiting bodies also provide protection against infection and predation of spores, through various structural (veils, setae, hairs, spikes) and chemical defence systems. Insecticidal and antimicrobial armouries are particularly rich in fruiting‐body‐forming fungi and include secondary metabolites, pore‐forming toxins (Plaza et al , ) and lectins, many of which are encoded by genes acquired horizontally from bacteria (Kunzler, ).…”

Entomotoxic and nematotoxic lectins and protease inhibitors from fungal fruiting bodies

“…In fungi, lectins have been implicated in defense against fungivores , in fungal developmental processes including fruiting body formation (Luan et al 2010;Swamy et al 2004;Wang et al 1998), in molecular recognition during mycorrhization or parasitism (Guillot et al 1994;Guillot and Konska 1997;Wang et al 1998), and in storage of nutrients (Kellens and Peumans 1990). Most experimental evidence is in support of the defensive function of fungal lectins, which is mediated by binding of the lectin to non-self glycans on the cells of the target organism (Künzler 2015). However, despite the recent reports of the successful identification of target glycoconjugates in insects and nematodes, the mechanism of action of many of these lectins is still unclear and the mechanisms may differ for the various lectins.…”

“…have been studied most thoroughly, and an ever increasing body of evidence confirms that they are part of a fungal innate defense system against predators and parasites (Künzler 2015;. Many reviews on mushroom lectins and protease inhibitors have been published recently but mainly viewing their potential application in human medicine (Dunaevsky et al 2014;Erjavec et al 2012;Hassan et al 2015;Kobayashi and Kawagishi 2014;Wong et al 2010;Xu et al 2011).…”