The family 42 carbohydrate-binding module of family 54 alpha-L-arabinofuranosidase specifically binds the arabinofuranose side chain of hemicellulose.
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.
Miyanaga
Akimasa
A
Department of Biotechnology, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan.
Koseki
Takuya
T
Miwa
Yozo
Y
Mese
Yuichiro
Y
Nakamura
Sachiko
S
Kuno
Atsushi
A
Hirabayashi
Jun
J
Matsuzawa
Hiroshi
H
Wakagi
Takayoshi
T
Shoun
Hirofumi
H
Fushinobu
Shinya
S
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
D005656:Fungal Proteins; D009844:Oligosaccharides; D011134:Polysaccharides; D014990:Xylans; C431714:arabinofuranose; C007916:hemicellulose; C085118:arabinoxylan; D001089:Arabinose; D006026:Glycoside Hydrolases; C019713:alpha-N-arabinofuranosidase