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Title
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High resolution structure and sequence of T. aurantiacus xylanase I: implications for the evolution of thermostability in family 10 xylanases and enzymes with (beta)alpha-barrel architecture.
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Authors
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L.Lo Leggio,
S.Kalogiannis,
M.K.Bhat,
R.W.Pickersgill.
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Ref.
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Proteins, 1999,
36,
295-306.
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PubMed id
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Abstract
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Xylanase I is a thermostable xylanase from the fungus Thermoascus aurantiacus,
which belongs to family 10 in the current classification of glycosyl hydrolases.
We have determined the three-dimensional X-ray structure of this enzyme to near
atomic resolution (1.14 A) by molecular replacement, and thereby corrected the
chemically determined sequence previously published. Among the five members of
family 10 enzymes for which the structure has been determined, Xylanase I from
T. aurantiacus and Xylanase Z from C. thermocellum are from thermophilic
organisms. A comparison with the three other available structures of the family
10 xylanases from mesophilic organisms suggests that thermostability is effected
mainly by improvement of the hydrophobic packing, favorable interactions of
charged side chains with the helix dipoles and introduction of prolines at the
N-terminus of helices. In contrast to other classes of proteins, there is very
little evidence for a contribution of salt bridges to thermostability in the
family 10 xylanases from thermophiles. Further analysis of the structures of
other proteins from thermophiles with eight-fold (beta)alpha-barrel architecture
suggests that favorable interactions of charged side chains with the helix
dipoles may be a common way in which thermophilic proteins with this fold are
stabilized. As this is the most common type of protein architecture, this
finding may provide a useful guide for site-directed mutagenesis aimed to
improve the thermostability of (beta)alpha-barrel proteins. Proteins
1999;36:295-306.
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