A novel family 8 xylanase, functional and physicochemical characterization.
Xylanases are generally classified into glycosyl hydrolase families 10 and 11 and are found to frequently have an inverse relationship between their pI and molecular mass values. However, we have isolated a psychrophilic xylanase that belongs to family 8 and which has both a high pI and high molecular mass. This novel xylanase, isolated from the Antarctic bacterium Pseudoalteromonas haloplanktis, is not homologous to family 10 or 11 enzymes but has 20-30% identity with family 8 members. NMR analysis shows that this enzyme hydrolyzes with inversion of anomeric configuration, in contrast to other known xylanases which are retaining. No cellulase, chitosanase or lichenase activity was detected. It appears to be functionally similar to family 11 xylanases. It hydrolyzes xylan to principally xylotriose and xylotetraose and is most active on long chain xylo-oligosaccharides. Kinetic studies indicate that it has a large substrate binding cleft, containing at least six xylose-binding subsites. Typical psychrophilic characteristics of a high catalytic activity at low temperatures and low thermal stability are observed. An evolutionary tree of family 8 enzymes revealed the presence of six distinct clusters. Indeed classification in family 8 would suggest an (alpha/alpha)(6) fold, distinct from that of other currently known xylanases.
Collins
Tony
T
Laboratory of Biochemistry, Institute of Chemistry B6, University of Liège, B-4000 Liège, Belgium.
Meuwis
Marie-Alice
MA
Stals
Ingeborg
I
Claeyssens
Marc
M
Feller
Georges
G
Gerday
Charles
C
D001483:Base Sequence; D002384:Catalysis; D002851:Chromatography, High Pressure Liquid; D002852:Chromatography, Ion Exchange; D017931:DNA Primers; D019143:Evolution, Molecular; D008969:Molecular Sequence Data; D020560:Proteobacteria / Q000201:enzymology / Q000254:growth & development; D013379:Substrate Specificity; D043325:Xylan Endo-1,3-beta-Xylosidase; D014995:Xylosidases / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*
D017931:DNA Primers; D014995:Xylosidases; D043325:Xylan Endo-1,3-beta-Xylosidase