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PDBsum entry 2d44
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References listed in PDB file
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Key reference
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Title
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The family 42 carbohydrate-Binding module of family 54 alpha-L-Arabinofuranosidase specifically binds the arabinofuranose side chain of hemicellulose.
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Authors
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A.Miyanaga,
T.Koseki,
Y.Miwa,
Y.Mese,
S.Nakamura,
A.Kuno,
J.Hirabayashi,
H.Matsuzawa,
T.Wakagi,
H.Shoun,
S.Fushinobu.
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Ref.
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Biochem J, 2006,
399,
503-511.
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PubMed id
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Abstract
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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.
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