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4,6-alpha-Glucanotransferase activity occurs more widespread in Lactobacillus strains and constitutes a separate GH70 subfamily

Leemhuis, H., Dijkman, W. P., Dobruchowska, J. M., Pijning, T., Grijpstra, P., Kralj, S., Kamerling, J. P., Dijkhuizen, L. & Gerwig, G. J., Jan-2013, In : Applied Microbiology and Biotechnology. 97, 1, p. 181-193 13 p.

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Family 70 glycoside hydrolase glucansucrase enzymes exclusively occur in lactic acid bacteria and synthesize a wide range of alpha-d-glucan (abbreviated as alpha-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)-alpha-d-glucooligosaccharides] as glucose donor substrates for alpha-glucan synthesis, acting as a 4,6-alpha-glucanotransferase (4,6-alpha GT) enzyme. Here, we report the characterization of two further GH70 4,6-alpha GT enzymes, i.e., from Lactobacillus reuteri strains DSM 20016 and ML1, which use maltooligosaccharides as glucose donor. Both enzymes cleave alpha 1 -> 4 glycosidic linkages and add the released glucose moieties one by one to the non-reducing end of growing linear alpha-glucan chains via alpha 1 -> 6 glycosidic linkages (alpha 1 -> 4 to alpha 1 -> 6 transfer activity). In this way, they convert pure maltooligosaccharide substrates into linear alpha-glucan product mixtures with about 50% alpha 1 -> 6 glycosidic bonds (isomalto/maltooligosaccharides). These new alpha-glucan products may provide an exciting type of carbohydrate for the food industry. The results show that 4,6-alpha GTs 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-alpha GT enzymes.

Original languageEnglish
Pages (from-to)181-193
Number of pages13
JournalApplied Microbiology and Biotechnology
Volume97
Issue number1
Publication statusPublished - Jan-2013

    Keywords

  • alpha-Glucan, Fiber, Glucansucrase, Glycoside hydrolase, 4,6-alpha-Glucanotransferase, Isomaltooligosaccharide, Starch, ALPHA-D-GLUCANS, STRUCTURAL-CHARACTERIZATION, MOLECULAR CHARACTERIZATION, NEISSERIA-POLYSACCHAREA, GLUCONOBACTER-OXYDANS, PRODUCT SPECIFICITY, DEXTRIN DEXTRANASE, REUTERI, ENZYMES, IDENTIFICATION

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