Differential recognition of plant cell walls by microbial xylan-specific carbohydrate-binding modules

Abstract

Glycoside hydrolases that degrade plant cell walls have complex molecular architectures in which one or more catalytic modules are appended to noncatalytic carbohydrate-binding modules (CBMs). CBMs promote binding to polysaccharides and potentiate enzymic hydrolysis. Although there are diverse sequence-based families of xylan-binding CBMs, these modules, in general, recognize both decorated and unsubstituted forms of the target polysaccharide, and thus the evolutionary rationale for this diversity is unclear. Using immunohistochemistry to interrogate the specificity of six xylan-binding CBMs for their target polysaccharides in cell walls has revealed considerable differences in the recognition of plant materials between these protein modules. Family 2b and 15 CBMs bind to xylan in secondary cell walls in a range of dicotyledon species, whereas family 4, 6, and 22 CBMs display a more limited capability to bind to secondary cell walls. A family 35 CBM, which displays more restricted ligand specificity against purified xylans than the other five protein modules, reveals a highly distinctive binding pattern to plant material including the recognition of primary cell walls of certain dicotyledons, a feature shared with CBM15. Differences in the specificity of the CBMs toward walls of wheat grain and maize coleoptiles were also evident. The variation in CBM specificity for ligands located in plant cell walls provides a biological rationale for the repertoire of structurally distinct xylanbinding CBMs present in nature, and points to the utility of these modules in probing the molecular architecture of cell walls.

The Biochemistry and Structural Biology of Plant Cell Wall Deconstruction

“…Thus, in CBM4, CBM6, and CBM22, xylan recognition is dominated by a single Xyl residue that is sandwiched between a pair of planar aromatic residues within a deep ligand-binding cleft (Czjzek et al, 2001;Charnock et al, 2002a;Simpson et al, 2002). While this binding mode confers higher affinity for isolated xylan chains, CBMs that recognize xylan through the asymmetric distribution of aromatic residues display more versatile ligand recognition; they are able to bind to the hemicellulose within in a variety of terrestrial plant cell walls, a specificity that is not displayed by the modules from CBM4, CBM6, and CBM22 (McCartney et al, 2006).…”

Pattern of Deposition of Cell Wall Polysaccharides and Transcript Abundance of Related Cell Wall Synthesis Genes during Differentiation in Barley Endosperm

“…Over the years, a number of molecular probes have been used to detect cellulose including histochemical stains such as Congo Red, the fluorophore/optical brightener Calcofluor white (FB28; Wood and Fulcher, 1978;Wood, 1980), and various carbohydrate-binding modules (CBMs;McCartney et al, 2006). However, to our knowledge, there is no probe for cellulose that does not also detect the (1→4)-b-oligoglucoside structures of (1→3, 1→4)-b-D-glucan and/or xyloglucan, including CBM3a (S. Wilson, unpublished data) and the CBM from Clostridium thermocellum directed toward crystalline cellulose Hervé et al, 2010).…”

Cellulose Binding Protein from the Parasitic Nematode Heterodera schachtii Interacts with Arabidopsis Pectin Methylesterase: Cooperative Cell Wall Modification during Parasitism

“…cnrs-mrs.fr/˜pedro/CAZY/cbm.html). CBDs also differ in their binding affinity and substrate specificity (Carrard et al, 2000;McCartney et al, 2006). In plant-parasitic nematodes, the first CBP gene to be identified was Mi CBP-1 from the root-knot nematode Meloidogyne incognita (Ding et al, 1998).…”