6Y9T

Family GH13_31 enzyme

Summary for 6Y9T

• Entry DOI: 10.2210/pdb6y9t/pdb
• Descriptor: Alpha-glucosidase, CALCIUM ION (3 entities in total)
• Functional Keywords: carbohydrate metabolism, disproportionating enzyme, gut microbiota, starch, hydrolase
• Biological source: Lactobacillus acidophilus NCFM
• Total number of polymer chains: 2
• Total formula weight: 130885.02

Authors

Andersen, S.,Poulsen, J.C.N.,Moeller, M.S.,Abou Hachem, M.,Lo Leggio, L. (deposition date: 2020-03-10, release date: 2020-05-27, Last modification date: 2024-01-24)

Primary citation

Andersen, S.,Moller, M.S.,Poulsen, J.N.,Pichler, M.J.,Svensson, B.,Lo Leggio, L.,Goh, Y.J.,Abou Hachem, M.
An 1,4-alpha-Glucosyltransferase Defines a New Maltodextrin Catabolism Scheme in Lactobacillus acidophilus.
Appl.Environ.Microbiol., 86:-, 2020

PubMed Abstract: The maltooligosaccharide (MOS) utilization locus in NCFM, a model for human small-intestine lactobacilli, encodes three glycoside hydrolases (GHs): a putative maltogenic α-amylase of family 13, subfamily 20 (GH13_20), a maltose phosphorylase of GH65 (GH65), and a family 13, subfamily 31, member (GH13_31B), annotated as a 1,6-α-glucosidase. Here, we reveal that GH13_31B is a 1,4-α-glucosyltransferase that disproportionates MOS with a degree of polymerization of ≥2, with a preference for maltotriose. Kinetic analyses of the three GHs encoded by the MOS locus revealed that the substrate preference of GH13_31B toward maltotriose complements the ~40-fold lower of GH13_20 toward this substrate, thereby enhancing the conversion of odd-numbered MOS to maltose. The concerted action of GH13_20 and GH13_31B confers the efficient conversion of MOS to maltose that is phosphorolyzed by GH65. Structural analyses revealed the presence of a flexible elongated loop that is unique for a previously unexplored clade of GH13_31, represented by GH13_31B. The identified loop insertion harbors a conserved aromatic residue that modulates the activity and substrate affinity of the enzyme, thereby offering a functional signature of this clade, which segregates from 1,6-α-glucosidases and sucrose isomerases previously described within GH13_31. Genomic analyses revealed that the GH13_31B gene is conserved in the MOS utilization loci of lactobacilli, including acidophilus cluster members that dominate the human small intestine. The 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 small intestine and considered beneficial to health. This study unveils a previously unknown scheme of maltooligosaccharide (MOS) catabolism via the concerted activity of an 1,4-α-glucosyltransferase together with a classical hydrolase and a phosphorylase. The intriguing involvement of a glucosyltransferase likely allows the fine-tuning of 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.

PubMed: 32444471
DOI: 10.1128/AEM.00661-20

Experimental method

X-RAY DIFFRACTION (2.78 Å)