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A β-Mannanase with a Lysozyme-like Fold and a Novel Molecular Catalytic Mechanism

DOI: 10.1021/acscentsci.6b00232 DOI Help

Authors: Yi Jin (University of York) , Marija Petricevic (University of Melbourne) , Alan John (University of Melbourne) , Lluís Raich (Departament de Química Inorgànica i Orgànica (Secció de Química Orgànica) & IQTCUB, Universitat de Barcelona) , Huw Jenkins (University of York) , Leticia Portela De Souza (University of York) , Fiona Cuskin (Newcastle University) , Harry J. Gilbert (Newcastle University) , Carme Rovira (Universitat de Barcelona; Institució Catalana de Recerca i Estudis Avançats (ICREA)) , Ethan D. Goddard-borger (ACRF Chemical Biology Division, The Walter and Eliza Hall Institute of Medical Research; University of Melbourne) , Spencer J. Williams (University of Melbourne) , Gideon J. Davies (University of York)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Acs Central Science

State: Published (Approved)
Published: November 2016
Diamond Proposal Number(s): 9948

Abstract: 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.

Subject Areas: Biology and Bio-materials, Chemistry

Instruments: I02-Macromolecular Crystallography