title: The family 42 carbohydrate-binding module of family 54 alpha-L-arabinofuranosidase specifically binds the arabinofuranose side chain of hemicellulose.
abstract: Alpha-L-arabinofuranosidase catalyses the hydrolysis of the alpha-1,2-, alpha-1,3-, and alpha-1,5-L-arabinofuranosidic bonds in L-arabinose-containing hemicelluloses such as arabinoxylan. AkAbf54 (the glycoside hydrolase family 54 alpha-L-arabinofuranosidase from Aspergillus kawachii) consists of two domains, a catalytic and an arabinose-binding domain. The latter has been named AkCBM42 [family 42 CBM (carbohydrate-binding module) of AkAbf54] because homologous domains are classified into CBM family 42. In the complex between AkAbf54 and arabinofuranosyl-alpha-1,2-xylobiose, the arabinose moiety occupies the binding pocket of AkCBM42, whereas the xylobiose moiety is exposed to the solvent. AkCBM42 was found to facilitate the hydrolysis of insoluble arabinoxylan, because mutants at the arabinose binding site exhibited markedly decreased activity. The results of binding assays and affinity gel electrophoresis showed that AkCBM42 interacts with arabinose-substituted, but not with unsubstituted, hemicelluloses. Isothermal titration calorimetry and frontal affinity chromatography analyses showed that the association constant of AkCBM42 with the arabinose moiety is approximately 10(3) M(-1). These results indicate that AkCBM42 binds the non-reducing-end arabinofuranosidic moiety of hemicellulose. To our knowledge, this is the first example of a CBM that can specifically recognize the side-chain monosaccharides of branched hemicelluloses.
authors.affiliation: Department of Biotechnology, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan.
authors.forename: Akimasa
authors.initials: A
authors.lastname: Miyanaga
authors.forename: Takuya
authors.initials: T
authors.lastname: Koseki
authors.forename: Yozo
authors.initials: Y
authors.lastname: Miwa
authors.forename: Yuichiro
authors.initials: Y
authors.lastname: Mese
authors.forename: Sachiko
authors.initials: S
authors.lastname: Nakamura
authors.forename: Atsushi
authors.initials: A
authors.lastname: Kuno
authors.forename: Jun
authors.initials: J
authors.lastname: Hirabayashi
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Matsuzawa
authors.forename: Takayoshi
authors.initials: T
authors.lastname: Wakagi
authors.forename: Hirofumi
authors.initials: H
authors.lastname: Shoun
authors.forename: Shinya
authors.initials: S
authors.lastname: Fushinobu
mesh_terms: D020816:Amino Acid Motifs; D001089:Arabinose / Q000031:analogs & derivatives* / Q000378:metabolism; D001230:Aspergillus / Q000201:enzymology*; D001665:Binding Sites; D002151:Calorimetry; D002846:Chromatography, Affinity; D018360:Crystallography, X-Ray; D004586:Electrophoresis; D005656:Fungal Proteins / Q000737:chemistry / Q000378:metabolism*; D006026:Glycoside Hydrolases / Q000737:chemistry / Q000378:metabolism*; D006868:Hydrolysis; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D009844:Oligosaccharides / Q000378:metabolism; D010843:Pichia; D011134:Polysaccharides / Q000737:chemistry / Q000378:metabolism*; D011485:Protein Binding; D011487:Protein Conformation; D012995:Solubility; D013379:Substrate Specificity; D014170:Transformation, Genetic; D014990:Xylans / Q000737:chemistry / Q000378:metabolism
chemical_list: D005656:Fungal Proteins; D009844:Oligosaccharides; D011134:Polysaccharides; D014990:Xylans; C431714:arabinofuranose; C007916:hemicellulose; C085118:arabinoxylan; D001089:Arabinose; D006026:Glycoside Hydrolases; C019713:alpha-N-arabinofuranosidase