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By means of QM(DFT)/MM metadynamics we have unraveled the hydrolytic reaction mechanism of Neisseria polysaccharea amylosucrase (NpAS), a member of GH13 family. Our results provide an atomistic picture of the active site reorganization along the catalytic double-displacement reaction, clarifying whether the glycosyl-enzyme reaction intermediate features an α-glucosyl unit in an undistorted 4 C 1 conformation, as inferred from structural studies, or a distorted 1 S 3-like conformation, as expected from mechanistic analysis of glycoside hydrolases (GHs). We show that, even though the first step of the reaction (glycosylation) results in a 4 C 1 conformation, the α-glucosyl unit undergoes an easy conformational change toward a distorted conformation as the active site preorganizes for the forthcoming reaction step (deglycosylation), in which an acceptor molecule, i.e., a water molecule for the hydrolytic reaction, performs a nucleophilic attack on the anomeric carbon. The two conformations (4 C 1 ad E 3) can be viewed as two different states of the glycosyl-enzyme intermediate (GEI), but only the E 3 state is preactivated for catalysis. These results are consistent with the general conformational itinerary observed for α-glucosidases.
Pubmed ID: 31114783 RIS Download
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Database that describes the families of structurally-related catalytic and carbohydrate-binding modules (or functional domains) of enzymes that degrade, modify, or create glycosidic bonds. This specialist database is dedicated to the display and analysis of genomic, structural and biochemical information on Carbohydrate-Active Enzymes (CAZymes). CAZy data are accessible either by browsing sequence-based families or by browsing the content of genomes in carbohydrate-active enzymes. New genomes are added regularly shortly after they appear in the daily releases of GenBank. New families are created based on published evidence for the activity of at least one member of the family and all families are regularly updated, both in content and in description. An original aspect of the CAZy database is its attempt to cover all carbohydrate-active enzymes across organisms and across subfields of glycosciences. One can search for CAZY Family pages using the Protein Accession (Genpept Accession, Uniprot Accession or PDB ID), Cazy family name or EC number. In addition, genomes can be searched using the NCBI TaxID. This search can be complemented by Google-based searches on the CAZy site.
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