4hk8
From Proteopedia
Crystal Structures of Mutant Endo- -1,4-xylanase II Complexed with substrate (1.15 A) and Products (1.6 A)
Structural highlights
FunctionXYN2_HYPJR Glycoside hydrolase involved in the hydrolysis of xylan, a major plant cell wall hemicellulose made up of 1,4-beta-linked D-xylopyranose residues. Catalyzes the endohydrolysis of the main-chain 1,4-beta-glycosidic bonds connecting the xylose subunits yielding various xylooligosaccharides and xylose (PubMed:1369024, Ref.5). The catalysis proceeds by a double-displacement reaction mechanism with a putative covalent glycosyl-enzyme intermediate, with retention of the anomeric configuration (PubMed:7988708). Produces xylobiose and xylose as the main degradation products (PubMed:19556747).[1] [2] [3] [4] Publication Abstract from PubMedXylanases catalyze the hydrolysis of plant hemicellulose xylan into oligosaccharides by cleaving the main-chain glycosidic linkages connecting xylose subunits. To study ligand binding and to understand how the pH constrains the activity of the enzyme, variants of the Trichoderma reesei xylanase were designed to either abolish its activity (E177Q) or to change its pH optimum (N44H). An E177Q-xylohexaose complex structure was obtained at 1.15 A resolution which represents a pseudo-Michaelis complex and confirmed the conformational movement of the thumb region owing to ligand binding. Co-crystallization of N44H with xylohexaose resulted in a hydrolyzed xylotriose bound in the active site. Co-crystallization of the wild-type enzyme with xylopentaose trapped an aglycone xylotriose and a transglycosylated glycone product. Replacing amino acids near Glu177 decreased the xylanase activity but increased the relative activity at alkaline pH. The substrate distortion in the E177Q-xylohexaose structure expands the possible conformational itinerary of this xylose ring during the enzyme-catalyzed xylan-hydrolysis reaction. X-ray crystallographic studies of family 11 xylanase Michaelis and product complexes: implications for the catalytic mechanism.,Wan Q, Zhang Q, Hamilton-Brehm S, Weiss K, Mustyakimov M, Coates L, Langan P, Graham D, Kovalevsky A Acta Crystallogr D Biol Crystallogr. 2014 Jan;70(Pt 1):11-23. doi:, 10.1107/S1399004713023626. Epub 2013 Dec 24. PMID:24419374[5] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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