title: A novel thermostable multidomain 1,4-beta-xylanase from 'Caldibacillus cellulovorans' and effect of its xylan-binding domain on enzyme activity.
abstract: The nucleotide sequence of the complete xynA gene, encoding a novel multidomain xylanase XynA of 'Caldibacillus cellulovorans', was determined by genomic-walking PCR. The putative XynA comprises an N-terminal domain (D1), recently identified as a xylan-binding domain (XBD), homologous to non-catalytic thermostabilizing domains from other xylanases. D1 is followed by a xylanase catalytic domain (D2) homologous to family 10 glycosyl hydrolases. Downstream of this domain two cellulose-binding domains (CBD), D3 and D4, were found linked via proline-threonine (PT)-rich peptides. Both CBDs showed sequence similarity to family IIIb CBDs. Upstream of xynA an incomplete open reading frame was identified, encoding a putative C-terminal CBD homologous to family IIIb CBDs. Two expression plasmids encoding the N-terminal XBD plus the catalytic domain (XynAd1/2) and the xylanase catalytic domain alone (XynAd2) were constructed and the biochemical properties of the recombinant enzymes compared. The absence of the XBD resulted in a decrease in thermostability of the catalytic domain from 70 degrees C (XynAd1/2) to 60 degrees C (XynAd2). Substrate-specificity experiments and analysis of the main products released from xylan hydrolysis indicate that both recombinant enzymes act as endo-1, 4-beta-xylanases, but differ in their ability to cleave small xylooligosaccharides.
authors.affiliation: Department of Biological Sciences, Macquarie University, North Ryde, Sydney, NSW 2109, Australia1.
authors.forename: Anwar
authors.initials: A
authors.lastname: Sunna
authors.affiliation: Department of Biological Sciences, Macquarie University, North Ryde, Sydney, NSW 2109, Australia1.
authors.forename: Moreland D
authors.initials: MD
authors.lastname: Gibbs
authors.affiliation: Department of Molecular Medicine, University of Auckland Medical School, Private Bag 92019, Auckland, New Zealand2.|Department of Biological Sciences, Macquarie University, North Ryde, Sydney, NSW 2109, Australia1.
authors.forename: Peter L
authors.initials: PL
authors.lastname: Bergquist
mesh_terms: D001406:Bacillaceae / Q000201:enzymology* / Q000235:genetics*; D001483:Base Sequence; D001665:Binding Sites / Q000235:genetics; D016384:Consensus Sequence; D017931:DNA Primers / Q000235:genetics; D043364:Endo-1,4-beta Xylanases; D004795:Enzyme Stability; D005798:Genes, Bacterial; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D020539:Sequence Analysis, Protein; D013379:Substrate Specificity; D013696:Temperature; D014990:Xylans / Q000378:metabolism; D014995:Xylosidases / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*
chemical_list: D017931:DNA Primers; D011994:Recombinant Proteins; D014990:Xylans; D014995:Xylosidases; D043364:Endo-1,4-beta Xylanases