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Publication Abstract from PubMed

Glycoside hydrolase (GH) family 5 is one of the largest GH families with various GH activities including lichenase, but the structural basis of the GH5 lichenase activity is still unknown. A novel thermostable lichenase F32EG5 belonging to GH5 was identified from an extremely thermophilic bacterium Caldicellulosiruptor sp. F32. F32EG5 is a bi-functional cellulose and lichenan-degrading enzyme and exhibited a high activity on beta-1,3-1,4-glucan but side activity on cellulose. Thin-layer chromatography and NMR analyses indicated that F32EG5 cleaved the beta-1,4 linkage or the beta-1,3 linkage while a 4- O -substitued glucose residue linked to a glucose residue through a beta-1,3 linkage, which is completely different from extensively studied GH16 lichenase that catalyses strict endo-hydrolysis of the beta-1,4-glycosidic linkage adjacent to a 3- O -substitued glucose residue in the mixed linked beta-glucans. The crystal structure of F32EG5 was determined to 2.8 A resolution and the crystal structure of the complex of F32EG5 E193Q mutant and cellotetraose was determined to 1.7 A resolution, which revealed that the exit subsites of substrate binding sites contribute to both thermostability and substrate specificity of F32EG5. The sugar chain showed a sharp bend in the complex structure, suggesting that a substrate cleft fitting to the bent sugar chains in lichenan is a common feature of GH5 lichenases. The mechanism of thermostability and substrate selectivity of F32EG5 was further demonstrated by molecular dynamics simulation and site-directed mutagenesis. These results provide biochemical and structural insight into thermostability and substrate selectivity of GH5 lichenases which have potential in industrial processes.

Structural Insights into the Substrate Specificity of a Glycoside Hydrolase Family 5 Lichenase from Caldicellulosiruptor sp. F32.,Meng DD, Liu X, Dong S, Wang YF, Ma XQ, Zhou H, Wang X, Yao LS, Feng Y, Li FL Biochem J. 2017 Aug 24. pii: BCJ20170328. doi: 10.1042/BCJ20170328. PMID:28838949^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.