title: A circularly permuted alpha-amylase-type alpha/beta-barrel structure in glucan-synthesizing glucosyltransferases.
abstract: A motif of amino acid residues, located at the active site and specific beta-strands in alpha-amylases, is recognized in alpha-1,3- and alpha-1,6-glucan-synthesizing glucosyltransferases, leading to the conclusion that these enzymes contain an alpha/beta-barrel closely related to the (beta/alpha)8-fold of the alpha-amylase superfamily. The secondary structure elements of the transferase barrel, however, are circularly permuted to start with an alpha-helix equivalent to helix 3 in the alpha-amylases. Thus, the transferase counterpart of the long third beta-->alpha connection--constituting a domain in the alpha-amylases--is divided to precede and succeed the barrel. This architectural arrangement may be coupled to sucrose scission and glucosyl transfer. The involvement in the mechanism in glucosyltransferases of active site residues recurring in amylolytic enzymes is discussed.
authors.affiliation: Department of Chemistry, University of Manitoba, Winnipeg, Canada.
authors.forename: E A
authors.initials: EA
authors.lastname: MacGregor
authors.forename: H M
authors.initials: HM
authors.lastname: Jespersen
authors.forename: B
authors.initials: B
authors.lastname: Svensson
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D005936:Glucans / Q000096:biosynthesis; D016695:Glycosyltransferases / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011487:Protein Conformation; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D013329:Structure-Activity Relationship; D000516:alpha-Amylases / Q000737:chemistry* / Q000378:metabolism
chemical_list: D005936:Glucans; D016695:Glycosyltransferases; D000516:alpha-Amylases