8c48
Crystal structure of Thermothelomyces thermophila GH30 (double mutant EE) in complex with xylopentaose
Structural highlights
FunctionXY30A_THET4 Xylanase exhibiting endo- and exo-xylanase activity (PubMed:31110561). Shows the highest activity toward beechwood glucuronoxylan, which consists of a beta-1,4-linked xylose backbone decorated with the methylated form of D-glucuronic acid (MeGlcA) attached directly to the main chain at xylose C2 (PubMed:31110561). Acts also against wheat arabinoxylan, a xylan without MeGlcA substituents along the main chain, but the xylanase activity is about two orders of magnitude lower than that achieved in the case of beechwood xylan (PubMed:31110561). Shows no activity against carob galactomannan, konjac glucomannan, or barley beta-glucan (PubMed:31110561). The recombinant xylanase also exhibits an exo-activity by releasing processively disaccharide units from the non-reducing end of linear and decorated xylooligosaccharides (XOS) (PubMed:31110561).[1] Publication Abstract from PubMedGlycoside hydrolase (GH) 30 family xylanases are enzymes of biotechnological interest due to their capacity to degrade recalcitrant hemicelluloses, such as glucuronoxylan (GX). This study focuses on a subfamily 7 GH30, TtXyn30A from Thermothelomyces thermophilus, which acts on GX in an "endo" and "exo" mode, releasing methyl-glucuronic acid branched xylooligosaccharides (XOs) and xylobiose, respectively. The crystal structure of inactive TtXyn30A in complex with 2(3)-(4-O-methyl-alpha-D-glucuronosyl)-xylotriose (UXX), along with biochemical analyses, corroborate the implication of E233, previously identified as alternative catalytic residue, in the hydrolysis of decorated xylan. At the -1 subsite, the xylose adopts a distorted conformation, indicative of the Michaelis complex of TtXyn30AEE with UXX trapped in the semi-functional active site. The most significant structural rearrangements upon substrate binding are observed at residues W127 and E233. The structures with neutral XOs, representing the "exo" function, clearly show the nonspecific binding at aglycon subsites, contrary to glycon sites, where the xylose molecules are accommodated via multiple interactions. Last, an unproductive ligand binding site is found at the interface between the catalytic and the secondary beta-domain which is present in all GH30 enzymes. These findings improve current understanding of the mechanism of bifunctional GH30s, with potential applications in the field of enzyme engineering. Structural and molecular insights into a bifunctional glycoside hydrolase 30 xylanase specific to glucuronoxylan.,Pentari C, Kosinas C, Nikolaivits E, Dimarogona M, Topakas E Biotechnol Bioeng. 2024 Apr 28. doi: 10.1002/bit.28731. PMID:38678481[2] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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