Functional Characterization of Endo- and Exo-Hydrolase Genes in Arabinan Degradation Gene Cluster of <i>Bifidobacterium longum</i> subsp. <i>suis</i>
Bifidobacteria are probiotic microorganisms commonly found in the gastrointestinal tract, some of which are known to utilize linear arabino-oligosaccharides (AOS) as prebiotic carbohydrates. In general, the synergistic actions of exo-type α-<span style="font-variant: small-caps;">l&l...
| Main Authors: | , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
MDPI AG
2024-03-01
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| Series: | International Journal of Molecular Sciences |
| Subjects: | |
| Online Access: | https://www.mdpi.com/1422-0067/25/6/3175 |
| Summary: | Bifidobacteria are probiotic microorganisms commonly found in the gastrointestinal tract, some of which are known to utilize linear arabino-oligosaccharides (AOS) as prebiotic carbohydrates. In general, the synergistic actions of exo-type α-<span style="font-variant: small-caps;">l</span>-arabinofuranosidases (ABFs) and endo-α-1,5-<span style="font-variant: small-caps;">l</span>-arabinanases (ABNs) are required for efficient arabinan degradation. In this study, the putative gene cluster for arabinan degradation was discovered in the genome of <i>Bifidobacterium longum</i> subsp. <i>suis</i>. It consists of a variety of genes encoding exo- and endo-hydrolases, sugar-binding proteins, ABC-binding cassettes, and transcriptional regulators. Among them, two endo-ABNs GH43 (BflsABN43A and BflsABN43B), two exo-ABFs GH43 (BflsABF43A and BflsABF43B), and an exo-ABF GH51 (BflsABF51) were predicted to be the key hydrolases for arabinan degradation. These hydrolase genes were functionally expressed in <i>Escherichia coli</i>, and their enzymatic properties were characterized. Their synergism in arabinan degradation has been proposed from the detailed modes of action. Extracellular endo-BflsABN43A hydrolyzes sugar beet and debranched arabinans into the short-chain branched and linear AOS. Intracellularly, AOS can be further degraded into <span style="font-variant: small-caps;">l</span>-arabinose via the cooperative actions of endo-BflsABN43B, exo-BflsABF43A with debranching activity, α-1,5-linkage-specific exo-BflsABF43B, and exo-BflsABF51 with dual activities. The resulting <span style="font-variant: small-caps;">l</span>-arabinose is expected to be metabolized into energy through the pentose phosphate pathway by three enzymes expressed from the <i>ara</i> operon of bifidobacteria. It is anticipated that uncovering arabinan utilization gene clusters and their detailed functions in the genomes of diverse microorganisms will facilitate the development of customized synbiotics. |
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| ISSN: | 1661-6596 1422-0067 |