A multidomain xylanase from a Bacillus sp. with a region homologous to thermostabilizing domains of thermophilic enzymes.
The gene xynC encoding xylanase C from Bacillus sp. BP-23 was cloned and expressed in Escherichia coli. The nucleotide sequence of a 3538 bp DNA fragment containing xynC gene was determined, revealing an open reading frame of 3258 bp that encodes a protein of 120,567 Da. A comparison of the deduced amino acid sequence of xylanase C with known beta-glycanase sequences showed that the encoded enzyme is a modular protein containing three different domains. The central region of the enzyme is the catalytic domain, which shows high homology to family 10 xylanases. A domain homologous to family IX cellulose-binding domains is located in the C-terminal region of xylanase C, whilst the N-terminal region of the enzyme shows homology to thermostabilizing domains found in several thermophilic enzymes. Xylanase C showed an activity profile similar to that of enzymes from mesophilic micro-organisms. Maximum activity was found at 45 degrees C, and the enzyme was only stable at 55 degrees C lower temperatures. Xylotetraose, xylotriose, xylobiose and xylose were the main products from birchwood xylan hydrolysis, whilst the enzyme showed increasing activity on xylo-oligosaccharides of increasing length, indicating that the cloned enzyme is an endoxylanase. A deletion derivative of xylanase C, lacking the region homologous to thermostabilizing domains, was constructed. The truncated enzyme showed a lower optimum temperature for activity than the full-length enzyme, 35 degrees C instead of 45 degrees C, and a reduced thermal stability that resulted in a complete inactivation of the enzyme after 2 h incubation at 55 degrees C.
Blanco
Ana
A
Department of Microbiology, Faculty of Biology, University of Barcelona, Avinguda Diagonal 645, 08028 Barcelona, Spain.
Díaz
Pilar
P
Department of Microbiology, Faculty of Biology, University of Barcelona, Avinguda Diagonal 645, 08028 Barcelona, Spain.
Zueco
Jesús
J
Department of Micorbiology, Faculty of Pharmacy, University of Valencia, Valencia, Spain.
Parascandola
Palma
P
Department of Chemical and Food Engineering, University of Salerno, Fisciano, Italy.
Pastor
F I Javier
FIJ
Department of Microbiology, Faculty of Biology, University of Barcelona, Avinguda Diagonal 645, 08028 Barcelona, Spain.
D000595:Amino Acid Sequence; D001407:Bacillus / Q000201:enzymology*; D020134:Catalytic Domain; D003001:Cloning, Molecular; D043364:Endo-1,4-beta Xylanases; D004795:Enzyme Stability; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics; D005798:Genes, Bacterial; D008969:Molecular Sequence Data; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D013379:Substrate Specificity; D013696:Temperature; D014995:Xylosidases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*
D014995:Xylosidases; D043364:Endo-1,4-beta Xylanases