Abstract
LysM motifs are carbohydrate-binding modules found in prokaryotes and eukaryotes. They bind to N-acetylglucosamine-containing carbohydrates, such as chitin, chitio-oligosaccharides and peptidoglycan. In this review, we summarize the features of the protein architecture of LysM-containing proteins in fungi and discuss their so far known biochemical properties, transcriptional profiles and biological functions. Further, based on data from evolutionary analyses and consensus pattern profiling of fungal LysM motifs, we show that they can be classified into a fungal-specific group and a fungal/bacterial group. This facilitates the classification and selection of further LysM proteins for detailed analyses and will contribute to widening our understanding of the functional spectrum of this protein family in fungi. Fungal LysM motifs are predominantly found in subgroup C chitinases and in LysM effector proteins, which are secreted proteins with LysM motifs but no catalytic domains. In enzymes, LysM motifs mediate the attachment to insoluble carbon sources. In plants, receptors containing LysM motifs are responsible for the perception of chitin-oligosaccharides and are involved in beneficial symbiotic interactions between plants and bacteria or fungi, as well as plant defence responses. In plant pathogenic fungi, LysM effector proteins have already been shown to have important functions in the dampening of host defence responses as well as protective functions of fungal hyphae against chitinases. However, the large number and diversity of proteins with LysM motifs that are being unravelled in fungal genome sequencing projects suggest that the functional repertoire of LysM effector proteins in fungi is only partially discovered so far.
Highlights
The abbreviation LysM is derived from the original name lysin motif, because they were first described in bacteriophage proteins (Birkeland 1994; Garvey et al 1986; Ponting et al 1999) where they were found as parts of lysins, which are hydrolytic enzymes that are responsible for cleaving the bacterial host’s cell wall during the final stage of the lytic cycle
The data from plant pathogenic fungi enabled exciting insights into the functions of LysM effector proteins in plant–pathogen interactions and their structural and biochemical properties, it needs to be acknowledged that fungi have a wide spectrum of diverse LysM effector proteins
Considering the different life styles of those fungi, it is likely that LysM proteins have additional biological functions and fine-tuned carbohydrate-binding properties still remain to be uncovered for this protein family
Summary
The abbreviation LysM is derived from the original name lysin motif, because they were first described in bacteriophage proteins (Birkeland 1994; Garvey et al 1986; Ponting et al 1999) where they were found as parts of lysins, which are hydrolytic enzymes that are responsible for cleaving the bacterial host’s cell wall during the final stage of the lytic cycle. Symbiotic interactions between mycorrhiza fungi and plants are mediated via LysM receptor kinases and mycorrhization factors, which are structurally similar to Nod factors and are chito-oligosaccharides modified by N-acylation and sulfation (Gough and Cullimore 2011; Gust et al 2012; Op den Camp et al 2011). LysMs are predominantly found in two types of proteins: (1) associated with catalytic protein modules This form is mainly in chitinases, where they define the protein architecture of subgroup C chitinases, which are found in the fungal kingdom (Gruber and Seidl-Seiboth 2012; Gruber et al 2011b). It should be mentioned that, depending on the fungal species, LysMs can be found in proteins containing other functional modules, e.g. CyanoVirin-N homology (CVNH) domains, N-acetylmuramoyl-Lalanine amidase domains and polysaccharide deacetylase type 1 domains (de Jonge and Thomma 2009; Koharudin et al 2011; Martinez et al 2012) and probably this list will have to be extended with the increasing number of fungal genomes that are being sequenced
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