Insights into Broad-Specificity Starch Modification from the Crystal Structure of Limosilactobacillus Reuteri NCC 2613 4,6-α-Glucanotransferase GtfB

Tjaard Pijning*, Joana Gangoiti, Evelien M Te Poele, Tim Börner, Lubbert Dijkhuizen

*Corresponding author for this work

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Abstract

GtfB-type α-glucanotransferase enzymes from glycoside hydrolase family 70 (GH70) convert starch substrates into α-glucans that are of interest as food ingredients with a low glycemic index. Characterization of several GtfBs showed that they differ in product- and substrate specificity, especially with regard to branching, but structural information is limited to a single GtfB, preferring mostly linear starches and featuring a tunneled binding groove. Here, we present the second crystal structure of a 4,6-α-glucanotransferase (Limosilactobacillus reuteri NCC 2613) and an improved homology model of a 4,3-α-glucanotransferase GtfB (L. fermentum NCC 2970) and show that they are able to convert both linear and branched starch substrates. Compared to the previously described GtfB structure, these two enzymes feature a much more open binding groove, reminiscent of and evolutionary closer to starch-converting GH13 α-amylases. Sequence analysis of 287 putative GtfBs suggests that only 20% of them are similarly "open" and thus suitable as broad-specificity starch-converting enzymes.

Original languageEnglish
Article number05657
Pages (from-to)13235-13245
Number of pages11
JournalJournal of Agricultural and Food Chemistry
Volume69
Issue number44
Early online date28-Oct-2021
DOIs
Publication statusPublished - Nov-2021

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