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Figure 1
General degradation pathway of the pectin backbones of polygalacturonan (PGA) and rhamnogalacturonan-I (RG-I) by bacterial enzymes to obtain monomers for metabolic processes. The PGA backbone is targeted at the 1–4 α-linkage between galacturonic acids (GalA) by pectate lyases and pectin lyases, which cleave the backbone until single and small polysaccharides remain. The reaction will leave a saturated and unsaturated GalA. The small polysaccharides containing terminal GalA are imported into the bacterium and then targeted by either UGL, URH or galacturonases to leave a saturated GalA and unsaturated GalA. The RG-I backbone is degraded in a similar fashion by RG lyases, leaving a saturated rhamnose (Rha) and a polysaccharide containing an unsaturated terminal GalA. The short-chain polysaccharides follow the same process as PGA polysaccharides, and once inside the cell are cleaved by URH, leaving a rhamnose and unsaturated GalA. In both instances the unsaturated GalA may spontaneously open to 4-­deoxy-L-threo-5-hexosulose-uronate. R– indicates polysaccharide side chains linked to both backbones. The backbones are also decorated with acetyl esters (ActEst) and methyl esters (MetEst).

ISSN: 2053-230X
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