The Bacteroidetes are a dominant bacterial phylum in the mammalian gastrointestinaltract and have a greatly expanded capacity for complex carbohy drate utilization. Most of the glycosidic potential within the Bacteroidetes is packaged into discrete polysaccharide utilization loci (PULs) that each encode a series of enzymes and cell-surface proteins that coordinate with a cognate TonB-dependent transporter in order to bind, degrade and import carbohydrate nutrition. PUL-encoded carbohydrate processing systems are referred to as “Sus-like systems” after the starch utilization system first described in Bacteroides thetaiotaomicron.
However, since the discovery of the Sus, similar systems have been found in the genomes of every gut associated Bacteroidetes, and many terrestrial and aquatic Bacteroidetes, extending a Sus-like paradigm for glycan uptake within this phylum. Our work over the past few years has described the protein structures of the surface glycan binding proteins (SGBPs) found within the Sus of B.thetaiotaomicron, as well other PUL-encoded Sus-like systems that target differentglycans. Here we describe our current work to determine how the SGBPs of varioushuman gut Bacteroides species allow cells toselect and import specific glycans from theintestinal environment.