An 1,4-α-glucosyltransferase defines a new maltodextrin catabolism scheme inLactobacillus acidophilus

Abstract

The maltooligosaccharide (MOS) utilization locus in Lactobacillus acidophilus NCFM, a model for human small-intestine lactobacilli, encodes a family 13 subfamily 31 glycoside hydrolase (GH13_31), annotated as an 1,6-α-glucosidase. Here, we reveal that this enzyme (LaGH13_31B) is an 1,4-α-glucosyltransferase that disproportionates MOS with preference for maltotriose. LaGH13_31B acts in concert with a maltogenic α-amylase that efficiently releases maltose from MOS larger than maltotriose. Collectively, these two enzymes promote efficient conversion of preferentially odd-numbered MOS to maltose that is phosphorolysed by a maltose phosphorylase, encoded by the same locus. Structural analyses revealed the presence of a flexible elongated loop, which is unique for LaGH13_31B and its close homologues. The identified loop insertion harbours a conserved aromatic residue that modulates the activity and substrate affinity of the enzyme, thereby offering a functional signature of this previously undescribed clade, which segregates from described activities such as 1,6-α-glucosidases and sucrose isomerases within GH13_31. Sequence analyses revealed that the LaGH13_31B gene is conserved in the MOS utilization loci of lactobacilli, including acidophilus cluster members that dominate the human small intestine.IMPORTANCEThe degradation of starch in the small intestine generates short linear and branched α-glucans. The latter are poorly digestible by humans, rendering them available to the gut microbiota e.g. lactobacilli adapted to the human small intestine and considered as beneficial to health. This study unveils a previously unknown scheme of maltooligosaccharide (MOS) catabolism, via the concerted action of activity together with a classical hydrolase and a phosphorylase. The intriguing involvement of a glucosyltransferase is likely to allow fine-tuning the regulation of MOS catabolism for optimal harnessing of this key metabolic resource in the human small intestine. The study extends the suite of specificities that have been identified in GH13_31 and highlights amino acid signatures underpinning the evolution of 1,4-α-glucosyl transferases that have been recruited in the MOS catabolism pathway in lactobacilli.

Niche-specific adaptation of Lactobacillus helveticus strains isolated from malt whisky and dairy fermentations

“…The genes encoding the two enzymes were located adjacently in the genome and were next to a gene encoding GH65-1 maltose phosphorylase, resulting in the formation of PUL-GH13-GH65 in the milk strain CNRZ32. Similar PUL organization was observed in several species in the L. acidophilus group [35]. The PUL was characterized by the release of maltose from maltooligosaccharides through the cooperation of two GH13 enzymes and further phosphorylation of maltose into βd-glucose 1-phosphate and glucose by the GH65 enzyme in L. acidophilus.…”

“…GH13-5 and GH13-7 included reference maltooligosaccharide/starch degrading enzymes of L. acidophilus [35]. The genes encoding the two enzymes were located adjacently in the genome and were next to a gene encoding GH65-1 maltose phosphorylase, resulting in the formation of PUL-GH13-GH65 in the milk strain CNRZ32.…”

“…Oligo-1,6-α-glucosidase and 1,4-α-glucosyltransferase of L. acidophilus NCFM, which cooperatively function in the hydrolysis of maltooligosaccharides/starch [35], belong to cluster 5 (GH13-5) and cluster 7 (GH13-7), respectively. GH13-5 and GH13-7 proteins were found in all whisky strains and 8 of the 14 milk strains.…”

An α type gluco-oligosaccharide from brown algae Laminaria japonica stimulated the growth of lactic acid bacteria encoding specific ABC transport system components

“…The GH1 gene was annotated as a series of β-type glycoside hydrolases, including multiple β-glucosidases, which might contribute to the degradation of β-glycosidic bonds in LJGO. The GH13 gene is an α-type hydrolase with 43 subfamilies, many of which are glucosidases that decompose starchrelated substrates 11 like the main structure in LJGO. However,…”

“…We also found that LAB can utilize α-glucans such as short, branched starches containing α-1,4and α-1,6-glucans and maltooligosaccharides that mainly contain α-1,4and branched α-1,6gluco-oligosaccharides. [11][12][13] The glycoside hydrolase family 13 (GH13) of α-glucosidases mainly decomposes α-1,4and α-1,6linked glucose residues and is widely distributed in LAB strains. However, most focus is directed towards the structural characterization of marine glucan and regulation of the gut microbiota structure, whereas the specific mechanisms of action of glucans on microorganisms have not been investigated in detail.…”