I. Connerton et al., A single domain thermophilic xylanase can bind insoluble xylan: evidence for surface aromatic clusters, BBA-PROT ST, 1433(1-2), 1999, pp. 110-121
Citations number
35
Categorie Soggetti
Biochemistry & Biophysics
Journal title
BIOCHIMICA ET BIOPHYSICA ACTA-PROTEIN STRUCTURE AND MOLECULAR ENZYMOLOGY
A clone expressing xylanase activity in Escherichia colt has been selected
from a genomic plasmid library of the thermophilic Bacillus strain D3. Subc
loning from the 9-kb insert located the xylanase activity to a 2.7-kb HindI
I/BamHI fragment. The DNA sequence of this clone revealed an ORF of 367 cod
ons encoding a single domain type-F or family 10 enzyme, which was designat
ed as XynA. Purification of the enzyme following over-expression in E. coli
produced an enzyme of 42 kDa with a temperature optimum of 75 degrees C wh
ich can efficiently bind and hydrolyse insoluble xylan. The pH optimum of t
he enzyme is 6.5, but it is active over a broad pH range. A homology model
of the xylanase has been constructed which reveals a series of surface arom
atic residues which form hydrophobic clusters. This unusual structural feat
ure is strikingly similar to the situation observed in the structure determ
ined for the type-G xylanase from the Bacillus D3 strain and may constitute
a common evolutionary mechanism imposed on different structural frameworks
by which these xylanases may bind potential substrates and exhibit thermos
tability. (C) 1999 Elsevier Science B.V. All rights reserved.