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A β-mannannase with a lysozyme fold and a novel molecular catalytic mechanism
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The enzymatic cleavage of β-1,4-mannans is achieved by endo-β-1,4-mannanases, enzymes involved in germination of seeds and microbial hemicellulose degradation, and which have increasing industrial and consumer product applications. β-Mannanases occur in a range of families of the CAZy sequence-based glycoside hydrolase (GH) classification scheme including families 5, 26, and 113. In this work we reveal that β-mannanases of the newly described GH family 134 differ from other mannanase families in both their mechanism and tertiary structure. A representative GH family 134 endo-β-1,4-mannanase from a Streptomyces sp. displays a fold closely related to that of hen egg white lysozyme but acts with inversion of stereochemistry. A Michaelis complex with mannopentaose, and a product complex with mannotriose, reveal ligands with pyranose rings distorted in an unusual inverted chair conformation. Ab initio quantum mechanics/molecular mechanics metadynamics quantified the energetically accessible ring conformations and provided evidence in support of a 1C4 → 3H4 → 3S1 conformational itinerary along the reaction coordinate. This work, in concert with that on GH family 124 cellulases, reveals how the lysozyme fold can be co-opted to catalyze the hydrolysis of different polysaccharides in a mechanistically distinct manner
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JIN, Yi, PETRICEVIC, Marija, JOHN, Alan, RAICH ARMENDÁRIZ, Lluís adrià, JENKINS, Huw, PORTELA DE SOUZA, Leticia, CUSKIN, Fiona, GILBERT, Harry j., ROVIRA I VIRGILI, Carme, GODDARD-BORGER, Ethan d., WILLIAMS, Spencer j., DAVIES, Gideon j.. A β-mannannase with a lysozyme fold and a novel molecular catalytic mechanism. _ACS Central Science_. 2016. Vol. 2, núm. 12, pàgs. 896-903. [consulta: 23 de gener de 2026]. ISSN: 2374-7951. [Disponible a: https://hdl.handle.net/2445/114446]