PDBsum entry 1k6a

Hydrolase

PDB id: 1k6a

Contents

Protein chain

302 a.a. *

Waters ×199

* Residue conservation analysis

PDB id:

1k6a

Name:

Hydrolase

Title:

Structural studies on the mobility in the active site of the thermoascus aurantiacus xylanase i

Structure:

Xylanase i. Chain: a. Synonym: endo-1,4-beta-xylanase. Ec: 3.2.1.8

Source:

Thermoascus aurantiacus. Organism_taxid: 5087. Strain: imi 216529

Resolution:

1.14Å R-factor: 0.109 R-free: 0.146

Authors:

L.Lo Leggio,S.Kalogiannis,K.Eckert,S.C.M.Teixeira,M.K.Bhat,C.Andrei, R.W.Pickersgill,S.Larsen

Key ref:

L.Lo Leggio et al. (2001). Substrate specificity and subsite mobility in T. aurantiacus xylanase 10A. FEBS Lett, 509, 303-308. PubMed id: 11741607 DOI: 10.1016/S0014-5793(01)03177-5

Date:

15-Oct-01 Release date: 03-Jul-02

Supersedes:

1fxm

Protein chain

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

Seq: 329 a.a.

Struc: 302 a.a.

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: 10.1016/S0014-5793(01)03177-5

FEBS Lett 509:303-308 (2001)

PubMed id: 11741607

Substrate specificity and subsite mobility in T. aurantiacus xylanase 10A.

L.Lo Leggio, S.Kalogiannis, K.Eckert, S.C.Teixeira, M.K.Bhat, C.Andrei, R.W.Pickersgill, S.Larsen.

ABSTRACT

The substrate specificity of Thermoascus aurantiacus xylanase 10A (TAX) has been investigated both biochemically and structurally. High resolution crystallographic analyses at 291 K and 100 K of TAX complexes with xylobiose show that the ligand is in its alpha anomeric conformation and provide a rationale for specificity on p-nitrophenyl glycosides at the -1 and -2 subsites. Trp 275, which is disordered in uncomplexed structures, is stabilised by its interaction with xylobiose. Two structural subsets in family 10 are identified, which differ by the presence or absence of a short helical stretch in the eighth betaalpha-loop of the TIM barrel, the loop bearing Trp 275. This structural difference is discussed in the context of Trp 275 mobility and xylanase function.

Selected figure(s)

Figure 1.
Fig. 1. Xylobiose and glycerol binding in TAX. TAX residues are shown for the XBCRYO structure in red, magenta (tryptophan residues forming the aromatic cage at subsite −1) or orange (catalytic glutamates). Xylobiose and water 75 in the XBCRYO structure is shown in blue. The sugar moieties occupying subsites −2, −1 and +1 in XBRT and water 319 are shown in cyan. Glycerol and water 203 from the GLC structure are shown in green. Potential hydrogen bonds with TAX (distances shorter than 3.2 Å) are coloured according to the same scheme as for the ligands. The substrate binding groove is oriented so that subsite −2 is at the top and subsite +1 is at the bottom. In panel b a Sigmaa F[obs]−F[calc] map calculated prior to incorporation of xylobiose in the model (blue) is shown for XBCRYO contoured at 2σ around 1.5 Å from xylobiose. In white the conformation of xylobiose bound to the P. simplicissimum xylanase (PDB code 1B3W), is shown for comparison. In panel c a simulated annealing 2F[obs]−F[calc] omit map is shown for the xylose at subsite +1 in the XBRT model (cyan) contoured at 0.7σ. The complexes of P. simplicissimum xylanase with xylotetraose (PDB code 1B3Y) and xylopentaose (PDB code 1B3Z) are shown in white, and the complex of P. fluorescens xylanase 10A with xylopentaose (PDB code 1E5N) is shown in purple for comparison.

Figure 2.
Fig. 2. Alternative conformations for Glu 46, Trp 275 and Arg 276 in the form II crystal.

The above figures are reprinted by permission from the Federation of European Biochemical Societies: FEBS Lett (2001, 509, 303-308) copyright 2001.

Figures were selected by an automated process.