The enzymatic cleavage of β-1,4-mannans is achieved by <i>endo </i>-β-1,4-mannanases, enzymes involved in germination of seeds and microbial hemicellulose degradation, and which have increasing industrial and consumer product applications. β-Mannana ...
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 1 C 4 → 3 H 4 ‡ → 3 S 1 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.
Organizational Affiliation:
Institute for Cell and Molecular Biosciences, The Medical School, Newcastle University , Framlington Place, Newcastle upon Tyne NE2 4HH, U.K.,Departament de Química Inorgànica i Orgànica (Secció de Química Orgànica) & IQTCUB, Universitat de Barcelona , 08028 Barcelona, Spain.,Departament de Química Inorgànica i Orgànica (Secció de Química Orgànica) & IQTCUB, Universitat de Barcelona, 08028 Barcelona, Spain; Institució Catalana de Recerca i Estudis Avançats (ICREA), 08020 Barcelona, Spain.,York Structural Biology Laboratory, Department of Chemistry, University of York , Heslington, YO10 5DD, U.K.,ACRF Chemical Biology Division, The Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria 3010, Australia; School of Chemistry and Bio21 Molecular Science and Biotechnology Institute and Department of Medical Biology, University of Melbourne, Parkville, Victoria 3010, Australia.,School of Chemistry and Bio21 Molecular Science and Biotechnology Institute and Department of Medical Biology, University of Melbourne , Parkville, Victoria 3010, Australia.
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