title: The Exiguobacterium sibiricum 255-15 GtfC Enzyme Represents a Novel Glycoside Hydrolase 70 Subfamily of 4,6-α-Glucanotransferase Enzymes.
abstract: The glycoside hydrolase 70 (GH70) family originally was established for glucansucrase enzymes found solely in lactic acid bacteria synthesizing α-glucan polysaccharides from sucrose (e.g., GtfA). In recent years, we have characterized GtfB and related Lactobacillus enzymes as 4,6-α-glucanotransferase enzymes. These GtfB-type enzymes constitute the first GH70 subfamily of enzymes that are unable to act on sucrose as a substrate but are active with maltodextrins and starch, cleave α1→4 linkages, and synthesize linear α1→6-glucan chains. The GtfB disproportionating type of activity results in the conversion of malto-oligosaccharides into isomalto/malto-polysaccharides with a relatively high percentage of α1→6 linkages. This paper reports the identification of the members of a second GH70 subfamily (designated GtfC enzymes) and the characterization of the Exiguobacterium sibiricum 255-15 GtfC enzyme, which is also inactive with sucrose and displays 4,6-α-glucanotransferase activity with malto-oligosaccharides. GtfC differs from GtfB in synthesizing isomalto/malto-oligosaccharides. Biochemically, the GtfB- and GtfC-type enzymes are related, but phylogenetically, they clearly constitute different GH70 subfamilies, displaying only 30% sequence identity. Whereas the GtfB-type enzyme largely has the same domain order as glucansucrases (with α-amylase domains A, B, and C plus domains IV and V), this GtfC-type enzyme differs in the order of these domains and completely lacks domain V. In GtfC, the sequence of conserved regions I to IV of clan GH-H is identical to that in GH13 (I-II-III-IV) but different from that in GH70 (II-III-IV-I because of a circular permutation of the (β/α)8 barrel. The GtfC 4,6-α-glucanotransferase enzymes thus represent structurally and functionally very interesting evolutionary intermediates between α-amylase and glucansucrase enzymes.
authors.affiliation: Microbial Physiology, Groningen Biomolecular Sciences and Biotechnology Institute (GBB), University of Groningen, Groningen, The Netherlands.
authors.forename: Joana
authors.initials: J
authors.lastname: Gangoiti
authors.affiliation: Biophysical Chemistry, Groningen Biomolecular Sciences and Biotechnology Institute (GBB), University of Groningen, Groningen, The Netherlands.
authors.forename: Tjaard
authors.initials: T
authors.lastname: Pijning
authors.affiliation: Microbial Physiology, Groningen Biomolecular Sciences and Biotechnology Institute (GBB), University of Groningen, Groningen, The Netherlands L.Dijkhuizen@rug.nl.
authors.forename: Lubbert
authors.initials: L
authors.lastname: Dijkhuizen
mesh_terms: D000595:Amino Acid Sequence; D056449:Bacillales / Q000737:chemistry / Q000145:classification / Q000201:enzymology* / Q000235:genetics; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006026:Glycoside Hydrolases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D005810:Multigene Family; D010802:Phylogeny; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment
chemical_list: D001426:Bacterial Proteins; D006026:Glycoside Hydrolases