PDBsum entry 1tux

Hydrolase

PDB id: 1tux

Contents

Protein chain

301 a.a. *

Waters ×266

* Residue conservation analysis

PDB id:

1tux

Name:

Hydrolase

Title:

High resolution crystal structure of a thermostable xylanase from thermoascus aurantiacus

Structure:

Xylanase. Chain: a. Ec: 3.2.1.8

Source:

Thermoascus aurantiacus. Organism_taxid: 5087. Strain: local indian soil. Other_details: fungal source from thermoascus aurantiacus xylanase

Resolution:

1.80Å R-factor: 0.160 R-free: 0.211

Authors:

R.Natesh,P.Bhanumoorthy,P.J.Vithayathil,K.Sekar,S.Ramakumar, M.A.Viswamitra

Key ref:

R.Natesh et al. (1999). Crystal structure at 1.8 A resolution and proposed amino acid sequence of a thermostable xylanase from Thermoascus aurantiacus. J Mol Biol, 288, 999. PubMed id: 10329194 DOI: 10.1006/jmbi.1999.2727

Date:

29-Oct-98 Release date: 22-Jul-99

Protein chain

P23360  (XYNA_THEAU) -  Endo-1,4-beta-xylanase from Thermoascus aurantiacus

Seq: 329 a.a.

Struc: 301 a.a.*

* PDB and UniProt seqs differ at 24 residue positions (black crosses)

Enzyme reactions

• Enzyme class: E.C.3.2.1.8 - endo-1,4-beta-xylanase.
• Reaction: Endohydrolysis of 1,4-beta-D-xylosidic linkages in xylans.

DOI no: 10.1006/jmbi.1999.2727

J Mol Biol 288:999 (1999)

PubMed id: 10329194

Crystal structure at 1.8 A resolution and proposed amino acid sequence of a thermostable xylanase from Thermoascus aurantiacus.

R.Natesh, P.Bhanumoorthy, P.J.Vithayathil, K.Sekar, S.Ramakumar, M.A.Viswamitra.

ABSTRACT

Thermoascus aurantiacus xylanase is a thermostable enzyme which hydrolyses xylan, a major hemicellulose component in the biosphere. Crystals belonging to P21 space group with a=41.7 A, b=68.1 A, c=51. 4 A and beta=113.6 degrees, Z=2 were grown that could diffract to better than 1.8 A resolution. The structure was solved by molecular replacement method using the Streptomyces lividans xylanase model. The amino acid sequence was determined from the electron density map aided by multiple alignment of related xylanase sequences. The sequence thus obtained provides a correction to the sequence reported earlier based on biochemical methods. The final refined protein model at 1.8 A resolution with 301 amino acid residues and 266 water molecules has an R-factor of 16.0 % and free R of 21.1 % with good stereochemistry. The single polypeptide chain assumes (alpha/beta)8 TIM-barrel fold and belongs to F/10 family of glycoside hydrolases. The active site consists of two glutamate residues located at the C terminus end of the beta-barrel, conforming to the double displacement mechanism for the enzyme action. A disulphide bond and more than ten salt bridges have been identified. In particular, the salt bridge Arg124-Glu232 which is almost buried, bridges the beta-strands beta4 and beta7 where the catalytic glutamate residues reside, and it may play a key role in the stability and activity at elevated temperature. To our knowledge, for the first time in the F/10 family xylanases, we observe a proline residue in the middle of the alpha-helix alpha6 which may be contributing to better packing. Earlier studies show that the enzyme retains its activity even at 70 degrees C. The refined protein model has allowed a detailed comparison with the other known structures in the F/10 family of enzymes. The possible causative factors for thermostability are discussed.

Selected figure(s)

Figure 2.
Figure 2. (a) Quality of the 2 F[o]−F[c] omit map (contoured at 1σ level) around the active site Glu237 after 50 cycles of positional refinement, omitting a stretch of residues around it from the refinement and electron density map calculation. (b) A representative electron density map showing the quality of the 2F[o]−F[c] electron density map contoured at 1σ level.

Figure 6.
Figure 6. Hydrogen bond network around the active site with some of the conserved water molecules in the active site labelled.

The above figures are reprinted by permission from Elsevier: J Mol Biol (1999, 288, 999-0) copyright 1999.

Figures were selected by an automated process.