Structural highlights
FunctionPublication Abstract from PubMedThe enzymatic cleavage of beta-1,4-mannans is achieved by endo-beta-1,4-mannanases, enzymes involved in germination of seeds and microbial hemicellulose degradation, and which have increasing industrial and consumer product applications. beta-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 beta-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-beta-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 --> 3H4double dagger --> 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. A beta-Mannanase with a Lysozyme-like Fold and a Novel Molecular Catalytic Mechanism.,Jin Y, Petricevic M, John A, Raich L, Jenkins H, Portela De Souza L, Cuskin F, Gilbert HJ, Rovira C, Goddard-Borger ED, Williams SJ, Davies GJ ACS Cent Sci. 2016 Dec 28;2(12):896-903. doi: 10.1021/acscentsci.6b00232. Epub, 2016 Nov 8. PMID:28058278[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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