1e5n

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spinqualitylabelsall models 1e5n, resolution 3.2Å Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image

E246C MUTANT OF P FLUORESCENS SUBSP. CELLULOSA XYLANASE A IN COMPLEX WITH XYLOPENTAOSE

Overview

The structure of the complex between a catalytically compromised family 10, xylanase and a xylopentaose substrate has been determined by X-ray, crystallography and refined to 3.2 A resolution. The substrate binds at, the C-terminal end of the eightfold betaalpha-barrel of Pseudomonas, fluorescens subsp. cellulosa xylanase A and occupies substrate binding, subsites -1 to +4. Crystal contacts are shown to prevent the expected mode, of binding from subsite -2 to +3, because of steric hindrance to subsite, -2. The loss of accessible surface at individual subsites on binding of, xylopentaose parallels well previously reported experimental measurements, of individual subsites binding energies, decreasing going from subsite +2, to +4. Nine conserved residues contribute to subsite -1, including three, tryptophan residues forming an aromatic cage around the xylosyl residue at, this subsite. One of these, Trp 313, is the single residue contributing, most lost accessible surface to subsite -1, and goes from a highly mobile, to a well-defined conformation on binding of the substrate. A comparison, of xylanase A with C. fimi CEX around the +1 subsite suggests that a, flatter and less polar surface is responsible for the better catalytic, properties of CEX on aryl substrates. The view of catalysis that emerges, from combining this with previously published work is the following: (1), xylan is recognized and bound by the xylanase as a left-handed threefold, helix; (2) the xylosyl residue at subsite -1 is distorted and pulled down, toward the catalytic residues, and the glycosidic bond is strained and, broken to form the enzyme-substrate covalent intermediate; (3) the, intermediate is attacked by an activated water molecule, following the, classic retaining glycosyl hydrolase mechanism.

About this Structure

1E5N is a Single protein structure of sequence from Pseudomonas fluorescens with CA as ligand. Active as Endo-1,4-beta-xylanase, with EC number 3.2.1.8 Full crystallographic information is available from OCA.

Reference

X-ray crystallographic study of xylopentaose binding to Pseudomonas fluorescens xylanase A., Leggio LL, Jenkins J, Harris GW, Pickersgill RW, Proteins. 2000 Nov 15;41(3):362-73. PMID:11025547

Page seeded by OCA on Tue Nov 20 13:47:18 2007