title: Carbohydrate-binding modules promote the enzymatic deconstruction of intact plant cell walls by targeting and proximity effects.
abstract: Cell wall degrading enzymes have a complex molecular architecture consisting of catalytic modules and noncatalytic carbohydrate-binding modules (CBMs). The function of CBMs in cell wall degrading processes is poorly understood. Here, we have evaluated the potential enzyme-targeting function of CBMs in the context of intact primary and secondary cell wall deconstruction. The capacity of a pectate lyase to degrade pectic homogalacturonan in primary cell walls was potentiated by cellulose-directed CBMs but not by xylan-directed CBMs. Conversely, the arabinofuranosidase-mediated removal of side chains from arabinoxylan in xylan-rich and cellulose-poor wheat grain endosperm cell walls was enhanced by a xylan-binding CBM but less so by a crystalline cellulose-specific module. The capacity of xylanases to degrade xylan in secondary cell walls was potentiated by both xylan- and cellulose-directed CBMs. These studies demonstrate that CBMs can potentiate the action of a cognate catalytic module toward polysaccharides in intact cell walls through the recognition of nonsubstrate polysaccharides. The targeting actions of CBMs therefore have strong proximity effects within cell wall structures, explaining why cellulose-directed CBMs are appended to many noncellulase cell wall hydrolases.
authors.affiliation: Faculty of Biological Sciences, Centre for Plant Sciences, University of Leeds, Leeds LS2 9JT, United Kingdom.
authors.forename: Cécile
authors.initials: C
authors.lastname: Hervé
authors.forename: Artur
authors.initials: A
authors.lastname: Rogowski
authors.forename: Anthony W
authors.initials: AW
authors.lastname: Blake
authors.forename: Susan E
authors.initials: SE
authors.lastname: Marcus
authors.forename: Harry J
authors.initials: HJ
authors.lastname: Gilbert
authors.forename: J Paul
authors.initials: JP
authors.lastname: Knox
mesh_terms: D002473:Cell Wall / Q000378:metabolism*; D002482:Cellulose / Q000378:metabolism; D043364:Endo-1,4-beta Xylanases / Q000378:metabolism; D006026:Glycoside Hydrolases / Q000378:metabolism; D018532:Pisum sativum / Q000378:metabolism; D010368:Pectins / Q000378:metabolism; D010940:Plant Proteins / Q000378:metabolism*; D010944:Plants / Q000378:metabolism*; D011133:Polysaccharide-Lyases / Q000378:metabolism; D011134:Polysaccharides / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000378:metabolism*; D014026:Nicotiana / Q000378:metabolism; D014908:Triticum / Q000378:metabolism; D014990:Xylans / Q000378:metabolism
chemical_list: D010940:Plant Proteins; D011134:Polysaccharides; D011956:Receptors, Cell Surface; D014990:Xylans; C055213:saccharide-binding proteins; D010368:Pectins; D002482:Cellulose; D006026:Glycoside Hydrolases; C019713:alpha-N-arabinofuranosidase; D043364:Endo-1,4-beta Xylanases; D011133:Polysaccharide-Lyases; C023911:pectate lyase; C003181:polygalacturonic acid