title: Alternansucrase acceptor reactions with D-tagatose and L-glucose.
abstract: Alternansucrase (EC 2.4.1.140) is a d-glucansucrase that synthesizes an alternating alpha-(1-->3), (1-->6)-linked d-glucan from sucrose. It also synthesizes oligosaccharides via d-glucopyranosyl transfer to various acceptor sugars. Two of the more efficient monosaccharide acceptors are D-tagatose and L-glucose. In the presence of d-tagatose, alternansucrase produced the disaccharide alpha-d-glucopyranosyl-(1-->1)-beta-D-tagatopyranose via glucosyl transfer. This disaccharide is analogous to trehalulose. We were unable to isolate a disaccharide product from L-glucose, but the trisaccharide alpha-D-glucopyranosyl-(1-->6)-alpha-d-glucopyranosyl-(1-->4)-l-glucose was isolated and identified. This is analogous to panose, one of the structural units of pullulan, in which the reducing-end D-glucose residue has been replaced by its L-enantiomer. The putative L-glucose disaccharide product, produced by glucoamylase hydrolysis of the trisaccharide, was found to be an acceptor for alternansucrase. The disaccharide, alpha-D-glucopyranosyl-(1-->4)-L-glucose, was a better acceptor than maltose, previously the best known acceptor for alternansucrase. A structure comparison of alpha-D-glucopyranosyl-(1-->4)-L-glucose and maltose was performed through computer modeling to identify common features, which may be important in acceptor affinity by alternansucrase.
authors.affiliation: Bioproducts and Biocatalysis Research Unit, National Center for Agricultural Utilization Research, Agricultural Research Service, United States Department of Agriculture, 1815 North University Street, Peoria, IL 61604, USA. cotegl@ncaur.usda.gov
authors.forename: Gregory L
authors.initials: GL
authors.lastname: Côté
authors.forename: Christopher A
authors.initials: CA
authors.lastname: Dunlap
authors.forename: Michael
authors.initials: M
authors.lastname: Appell
authors.forename: Frank A
authors.initials: FA
authors.lastname: Momany
mesh_terms: D001665:Binding Sites; D002240:Carbohydrate Sequence; D004187:Disaccharides / Q000737:chemistry / Q000378:metabolism; D005947:Glucose / Q000737:chemistry / Q000378:metabolism*; D016695:Glycosyltransferases / Q000378:metabolism*; D006601:Hexoses / Q000737:chemistry / Q000378:metabolism*; D008969:Molecular Sequence Data; D015394:Molecular Structure; D013237:Stereoisomerism; D013329:Structure-Activity Relationship; D013816:Thermodynamics
chemical_list: D004187:Disaccharides; D006601:Hexoses; D016695:Glycosyltransferases; C033837:alternansucrase; D005947:Glucose; C030192:tagatose