The human large intestine is home to a diverse microbial community, the gut microbiome, which is essential for human health. Complex dietary glycans that are inaccessible to the enzymes of the human digestive tract are the primary nutrient source for the microbiome, and the utilization of these complex sugars is essential for their survival. This utilization is integral to mutualism between host and bacteria, leading, for example, to the generation of short-chain fatty acids that are associated with normal gastrointestinal physiology and systemic health benefits to the host. The distal gut microbiome is dominated by two bacterial phyla: the Gram-positive Firmicutes, and the Gram-negative Bacteroidetes. The outer membrane (OM) of Gram-negative bacteria presents a formidable barrier to the uptake of large nutrients and gut Bacteroidetes use a common strategy for glycan utilization, wherein the machinery for the uptake, processing, transport and metabolism of glycans is encoded in co-regulated gene clusters known as polysaccharide utilization loci (PULs). Glycan transport across the OM is dependent on the SusCD core components of a PUL. SusC is an integral OM, TonB-dependent active transporter, whereas SusD is a surface-exposed OM lipoprotein. SusCD complexes exist as SusC2D2 tetramers, creating a core transportation unit with a twin barrel structure, in which each barrel is associated with its own SusD that caps the extracellular face of the transporter. Here you can see a recent cryoEM structure of the SusC components of the dextran utilisation system from Bacteroides thetaiotaomicron (PDB code: 8AA4)
#molecularart ... #immolecular ... #bacteriodes ... #gut ... #microbiome ... #dextran ... #betabarrel ... #membrane ... #transport ... #cryoem
Structure rendered with @proteinimaging and depicted with @corelphotopaint
#molecularart ... #immolecular ... #bacteriodes ... #gut ... #microbiome ... #dextran ... #betabarrel ... #membrane ... #transport ... #cryoem
Structure rendered with @proteinimaging and depicted with @corelphotopaint
