title: 4,6-α-Glucanotransferase activity occurs more widespread in Lactobacillus strains and constitutes a separate GH70 subfamily.
abstract: Family 70 glycoside hydrolase glucansucrase enzymes exclusively occur in lactic acid bacteria and synthesize a wide range of α-D-glucan (abbreviated as α-glucan) oligo- and polysaccharides. Of the 47 characterized GH70 enzymes, 46 use sucrose as glucose donor. A single GH70 enzyme was recently found to be inactive with sucrose and to utilize maltooligosaccharides [(1→4)-α-D-glucooligosaccharides] as glucose donor substrates for α-glucan synthesis, acting as a 4,6-α-glucanotransferase (4,6-αGT) enzyme. Here, we report the characterization of two further GH70 4,6-αGT enzymes, i.e., from Lactobacillus reuteri strains DSM 20016 and ML1, which use maltooligosaccharides as glucose donor. Both enzymes cleave α1→4 glycosidic linkages and add the released glucose moieties one by one to the non-reducing end of growing linear α-glucan chains via α1→6 glycosidic linkages (α1→4 to α1→6 transfer activity). In this way, they convert pure maltooligosaccharide substrates into linear α-glucan product mixtures with about 50% α1→6 glycosidic bonds (isomalto/maltooligosaccharides). These new α-glucan products may provide an exciting type of carbohydrate for the food industry. The results show that 4,6-αGTs occur more widespread in family GH70 and can be considered as a GH70 subfamily. Sequence analysis allowed identification of amino acid residues in acceptor substrate binding subsites +1 and +2, differing between GH70 GTF and 4,6-αGT enzymes.
authors.affiliation: Microbial Physiology, Groningen Biomolecular Sciences and Biotechnology Institute (GBB), University of Groningen, Nijenborgh 7, 9747 AG, Groningen, The Netherlands.
authors.forename: Hans
authors.initials: H
authors.lastname: Leemhuis
authors.forename: Willem P
authors.initials: WP
authors.lastname: Dijkman
authors.forename: Justyna M
authors.initials: JM
authors.lastname: Dobruchowska
authors.forename: Tjaard
authors.initials: T
authors.lastname: Pijning
authors.forename: Pieter
authors.initials: P
authors.lastname: Grijpstra
authors.forename: Slavko
authors.initials: S
authors.lastname: Kralj
authors.forename: Johannis P
authors.initials: JP
authors.lastname: Kamerling
authors.forename: Lubbert
authors.initials: L
authors.lastname: Dijkhuizen
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D005936:Glucans / Q000378:metabolism*; D006004:Glycogen Debranching Enzyme System / Q000235:genetics* / Q000378:metabolism*; D052200:Limosilactobacillus reuteri / Q000201:enzymology* / Q000235:genetics; D008969:Molecular Sequence Data; D009844:Oligosaccharides / Q000378:metabolism*; D017422:Sequence Analysis, DNA
chemical_list: D004269:DNA, Bacterial; D005936:Glucans; D006004:Glycogen Debranching Enzyme System; D009844:Oligosaccharides; C021705:maltooligosaccharides; C020569:4 alpha-glucanotransferase