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. 2021 Feb 3;13(1):1848158. doi: 10.1080/19490976.2020.1848158

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© 2021 The Author(s). Published with license by Taylor & Francis Group, LLC.

This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Figure 2. — The starch utilization system (Sus) of Bacteroides thetaiotaomicron.

SusC is a TonB-dependent transporter that works in collaboration with the starch bindinglipoproteins SusD, SusE and SusF. These lipoproteins play roles in binding and immobilizing the extracellular starch polymers. Subsequently, SusG, an α-amylase, degrades the starch into smaller oligosaccharides which proceed to the periplasm via SusC. In the periplasm, SusA (α-amylase) and SusB (α-glucosidase) breakdown the oligosaccharides into maltose and glucose. These di- and mono-saccharides are transported into the cytoplasm via sugar transporting permeases. The sensor/regulator, SusR, (sensor domain in the periplasm; DNA binding domain in the cytoplasm) regulates the expression of the susA-G genes in response to maltose in the periplasm. The Sus system of Bth gives it an advantage in the competitive gut environment and also assists in the attachment to mucus glycans.