Starch degradation

Starch (alfa 1,4 and alfa 1,6 glucan) is processed by gut microbiota (e.g., Bacteroides thetaiotaomicron)

Functional model of glycan processing based on the eight-gene Bacteroides thetaiotaomicron starch utilization system (Sus)). Individual starch processing steps are:

• Step 1: Glycans pass through the superficial capsular polysaccharide layer.


• Step 2: Glycans are bound by components associated with the outer membrane, such as SusD, which makes direct contact with starch due to the three-dimensional structure of its helices.


• Step 3: Surface-bound glycans are degraded by outer membrane-associated glycoside hydrolases such as SusG, resulting in smaller oligosaccharides transported across the outer membrane by SusC-like proteins.


• Step 4: Oligosaccharides are broken down into their component monosaccharides or disaccharides by periplasmic glycan-degrading enzymes such as SusA and SusB.


• Steps 5 and 6, released saccharides, serve as signals for transcription regulators that activate the polysaccharide utilization locus (PUL)) gene expression.


• Step 7, depolymerized sugars are imported across the cytoplasmic membrane.

Martens et al. 2009 J Biol Chem. 284: 24673-24677