Probing the Functions of Carbohydrate Binding Modules in the CBEL Protein from the Oomycete Phytophthora parasitica

Abstract

Oomycetes are microorganisms that are distantly related to true fungi and many members of this phylum are major plant pathogens. Oomycetes express proteins that are able to interact with plant cell wall polysaccharides, such as cellulose. This interaction is thought to be mediated by carbohydrate-binding modules that are classified into CBM family 1 in the CAZy database. In this study, the two CBMs (1–1 and 1–2) that form part of the cell wall glycoprotein, CBEL, from Phytophthora parasitica have been submitted to detailed characterization, first to better quantify their interaction with cellulose and second to determine whether these CBMs can be useful for biotechnological applications, such as biomass hydrolysis. A variety of biophysical techniques were used to study the interaction of the CBMs with various substrates and the data obtained indicate that CBEL’s CBM1-1 exhibits much greater cellulose binding ability than CBM1-2. Engineering of the family 11 xylanase from Talaromyces versatilis (TvXynB), an enzyme that naturally bears a fungal family 1 CBM, has produced two variants. The first one lacks its native CBM, whereas the second contains the CBEL CBM1-1. The study of these enzymes has revealed that wild type TvXynB binds to cellulose, via its CBM1, and that the substitution of its CBM by oomycetal CBM1-1 does not affect its activity on wheat straw. However, intriguingly the addition of CBEL during the hydrolysis of wheat straw actually potentiates the action of TvXynB variant lacking a CBM1. This suggests that the potentiating effect of CBM1-1 might not require the formation of a covalent linkage to TvXynB.

Multimodularity of a GH10 Xylanase Found in the Termite Gut Metagenome

“…were all purchased from Megazyme (Bray, Ireland). Cellulose nanocrystals from cotton linters were prepared as previously described (35). Oligonucleotide primers were purchased from Eurogentec (Liège, Belgium) ( Table 1).…”

Proteomic Analysis of Phytophthora infestans Reveals the Importance of Cell Wall Proteins in Pathogenicity

“…These two amino acids are in one of the cellulose binding domains (CBD) of CBEL and mutating Y188 to alanine has been demonstrated to reduce CBEL necrosis-inducing activity in planta (48), indicating that these residues are important for the ability of CBEL to function as an elicitor. However, a search of the SMART database (http:// smart.embl-heidelberg.de/) identified neither a CBD, nor an Apple domain, the two domains comprising CBEL (49). In our opinion this makes it less likely that PITG_01973 has the same biological role as CBEL.…”

Phytophthora palmivora–Cocoa Interaction

“…By expressing the Arabidopsis lectin receptor kinase LecRK-I.9 gene in potato and N. benthamiana , late blight resistance to P. infestans was significantly enhanced [ 112 ]. Cellulose-binding elicitor lectins (CBELs) are cell wall-localized glycoproteins involved in cell wall organization and the adhesion of the mycelium to cellulosic substrates [ 113 , 114 , 115 ]. They have also been shown to aid in Phytophthora ’s penetration into its plant host by mediating the oomycete’s attachment to the host surface [ 113 , 114 , 115 ].…”