1bk1
From Proteopedia
|
ENDO-1,4-BETA-XYLANASE C
Overview
Xylanase C from Aspergillus kawachii has an optimum pH of 2.0 and is stable at pH 1.0. The crystal structure of xylanase C was determined at 2.0 A resolution (R-factor = 19.4%). The overall structure was similar to those of other family 11 xylanases. Asp37 and an acid-base catalyst, Glu170, are located at a hydrogen-bonding distance (2.8 A), as in other xylanases with low pH optima. Asp37 of xylanase C was replaced with asparagine and other residues by site-directed mutagenesis. Analyses of the wild-type and mutant enzymes showed that Asp37 is important for high enzyme activity at low pH. In the case of the asparagine mutant, the optimum pH shifted to 5.0 and the maximum specific activity decreased to about 15% of that of the wild-type enzyme. On structural comparison with xylanases with higher pH optima, another striking feature of the xylanase C structure was found; the enzyme has numerous acidic residues concentrated on the surface (so-called 'Ser/Thr surface' in most family 11 xylanases). The relationship of the stability against extreme pH conditions and high salt concentrations with the spatially biased distribution of charged residues on the proteins is discussed.
About this Structure
1BK1 is a Single protein structure of sequence from Aspergillus kawachii. Active as Endo-1,4-beta-xylanase, with EC number 3.2.1.8 Known structural/functional Site: . Full crystallographic information is available from OCA.
Reference
Crystallographic and mutational analyses of an extremely acidophilic and acid-stable xylanase: biased distribution of acidic residues and importance of Asp37 for catalysis at low pH., Fushinobu S, Ito K, Konno M, Wakagi T, Matsuzawa H, Protein Eng. 1998 Dec;11(12):1121-8. PMID:9930661
Page seeded by OCA on Thu Feb 21 11:56:09 2008
