5e6y
Crystal structure of E.Coli branching enzyme in complex with alpha cyclodextrin
Structural highlights
FunctionGLGB_ECO24 Catalyzes the formation of the alpha-1,6-glucosidic linkages in glycogen by scission of a 1,4-alpha-linked oligosaccharide from growing alpha-1,4-glucan chains and the subsequent attachment of the oligosaccharide to the alpha-1,6 position. Publication Abstract from PubMedBranching enzyme (BE) is responsible for the third step in glycogen/starch biosynthesis. It catalyzes the cleavage of alpha-1,4 glucan linkages and subsequent reattachment to form alpha-1,6 branch points. These branches are crucial to the final structure of glycogen and starch. The crystal structures of Escherichia coli BE (EcBE) in complex with alpha-, beta- and gamma-cyclodextrin were determined in order to better understand substrate binding. Four cyclodextrin-binding sites were identified in EcBE; they were all located on the surface of the enzyme, with none in the vicinity of the active site. While three of the sites were also identified as linear polysaccharide-binding sites, one of the sites is specific for cyclodextrins. In previous work three additional binding sites were identified as exclusively binding linear malto-oligosaccharides. Comparison of the binding sites shed light on this apparent specificity. Binding site IV is located in the carbohydrate-binding module 48 (CBM48) domain of EcBE and superimposes with the cyclodextrin-binding site found in the CBM48 domain of 5'-AMP-activated protein kinase (AMPK). Comparison of these sites shows the similarities and differences in the two binding modes. While some of the binding sites were found to be conserved between branching enzymes of different organisms, some are quite divergent, indicating both similarities and differences between oligosaccharide binding in branching enzymes from various sources. Crystal structures of Escherichia coli branching enzyme in complex with cyclodextrins.,Feng L, Fawaz R, Hovde S, Sheng F, Nosrati M, Geiger JH Acta Crystallogr D Struct Biol. 2016 May 1;72(Pt 5):641-7. doi:, 10.1107/S2059798316003272. Epub 2016 Apr 26. PMID:27139627[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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