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

作者：Jin Yi; Petricevic Marija; John Alan; Raich Lluis; Jenkins Huw; De Souza Leticia Portela; Cuskin Fiona; Gilbert Harry J; Rovira Carme^*; Goddard Borger Ethan D^*; Williams Spencer J^*; Davies Gideon J^*

来源：ACS Central Science, 2016, 2(12): 896-903.

DOI：10.1021/acscentsci.6b00232

The 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 C-1(4) -> H-3(4)double dagger -> S-3(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.

• 出版日期2016-12-28
• 单位河北医科大学