A bifunctional enzyme, with separate xylanase and beta(1,3-1,4)-glucanase domains, encoded by the xynD gene of Ruminococcus flavefaciens.
Adjacent regions of a Ruminococcus flavefaciens 17 DNA fragment were found to encode xylanase and beta(1,3-1,4)-glucanase activities. Sequencing of this fragment showed that both activities are encoded by a single 2,406-bp open reading frame corresponding to the xynD gene. The predicted product has a characteristic signal sequence that is followed by an amino-terminal domain related to family G xylanases, while the carboxyterminal domain is related to beta(1,3-1,4)-glucanases from several other bacterial species. These two domains are connected by a region of unknown function that consists of 309 amino acids and includes a 30-amino-acid threonine-rich sequence. A polypeptide having a molecular weight of approximately 90,000 and exhibiting xylanase and beta(1,3-1,4)-glucanase activities was detected in Escherichia coli cells carrying the cloned xynD gene. This is one of the first cases in which a microbial polysaccharidase has been shown to carry separate catalytic domains active against different plant cell wall polysaccharides within the same polypeptide. xynD is one of a family of related genes in R. flavefaciens that encode enzymes having multiple catalytic domains, and the amino terminus of XYLD exhibits a high degree of similarity with the corresponding regions of another xylanase, XYLA, which carries two different xylanase catalytic domains.
Rowett Research Institute, Bucksburn, Aberdeen, United Kingdom.
H J
HJ
Flint
J
J
Martin
C A
CA
McPherson
A S
AS
Daniel
J X
JX
Zhang
D000595:Amino Acid Sequence; D001483:Base Sequence; D043364:Endo-1,4-beta Xylanases; D004926:Escherichia coli / Q000235:genetics; D005798:Genes, Bacterial / Q000235:genetics*; D006026:Glycoside Hydrolases / Q000096:biosynthesis / Q000235:genetics*; D006095:Gram-Positive Cocci / Q000201:enzymology* / Q000235:genetics*; D008969:Molecular Sequence Data; D009097:Multienzyme Complexes / Q000235:genetics; D005810:Multigene Family / Q000235:genetics; D016366:Open Reading Frames / Q000235:genetics; D021382:Protein Sorting Signals / Q000235:genetics; D011994:Recombinant Proteins / Q000096:biosynthesis; D017386:Sequence Homology, Amino Acid; D013912:Threonine / Q000235:genetics; D043325:Xylan Endo-1,3-beta-Xylosidase
D009097:Multienzyme Complexes; D021382:Protein Sorting Signals; D011994:Recombinant Proteins; D013912:Threonine; D006026:Glycoside Hydrolases; D043325:Xylan Endo-1,3-beta-Xylosidase; C028020:licheninase; D043364:Endo-1,4-beta Xylanases