The Exiguobacterium sibiricum 255-15 GtfC Enzyme Represents a Novel Glycoside Hydrolase 70 Subfamily of 4,6-?-Glucanotransferase Enzymes.

ABSTRACT: The glycoside hydrolase 70 (GH70) family originally was established for glucansucrase enzymes found solely in lactic acid bacteria synthesizing ?-glucan polysaccharides from sucrose (e.g., GtfA). In recent years, we have characterized GtfB and related Lactobacillus enzymes as 4,6-?-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 ?1?4 linkages, and synthesize linear ?1?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 ?1?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-?-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 ?-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 (?/?)8 barrel. The GtfC 4,6-?-glucanotransferase enzymes thus represent structurally and functionally very interesting evolutionary intermediates between ?-amylase and glucansucrase enzymes.

SUBMITTER: Gangoiti J 

PROVIDER: S-EPMC4711130 | biostudies-literature | 2016 Jan

REPOSITORIES: biostudies-literature