The Sus operon: a model system for starch uptake by the human gut Bacteroidetes

Resident bacteria in the densely populated human intestinal tract must efficiently compete for carbohydrate nutrition. The Bacteroidetes, a dominant bacterial phylum in the mammalian gut, encode a plethora of discrete polysaccharide utilization loci (PULs) that are selectively activated to facilitat...

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Bibliographic Details
Published in:Cellular and molecular life sciences : CMLS 2016-07, Vol.73 (14), p.2603-2617
Main Authors: Foley, Matthew H., Cockburn, Darrell W., Koropatkin, Nicole M.
Format: Article
Language:English
Subjects:
Bacteria
Bacterial Proteins - chemistry
Bacterial Proteins - metabolism
Bacteroidetes - metabolism
Biochemistry
Biomedical and Life Sciences
Biomedicine
Carbohydrates
Cell Biology
Digestive system
Gastrointestinal Tract - microbiology
Humans
Life Sciences
Models, Biological
Multi-Author Review
Nutrition
Operon - genetics
Proteins
Starch - metabolism
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Summary:Resident bacteria in the densely populated human intestinal tract must efficiently compete for carbohydrate nutrition. The Bacteroidetes, a dominant bacterial phylum in the mammalian gut, encode a plethora of discrete polysaccharide utilization loci (PULs) that are selectively activated to facilitate glycan capture at the cell surface. The most well-studied PUL-encoded glycan-uptake system is the starch utilization system (Sus) of Bacteroides thetaiotaomicron. The Sus includes the requisite proteins for binding and degrading starch at the surface of the cell preceding oligosaccharide transport across the outer membrane for further depolymerization to glucose in the periplasm. All mammalian gut Bacteroidetes possess analogous Sus-like systems that target numerous diverse glycans. In this review, we discuss what is known about the eight Sus proteins of B. thetaiotaomicron that define the Sus-like paradigm of nutrient acquisition that is exclusive to the Gram-negative Bacteroidetes. We emphasize the well-characterized outer membrane proteins SusDEF and the α-amylase SusG, each of which have unique structural features that allow them to interact with starch on the cell surface. Despite the apparent redundancy in starch-binding sites among these proteins, each has a distinct role during starch catabolism. Additionally, we consider what is known about how these proteins dynamically interact and cooperate in the membrane and propose a model for the formation of the Sus outer membrane complex.
ISSN:1420-682X
1420-9071
DOI:10.1007/s00018-016-2242-x