Rhamnolipids (RL) consist of a fatty acyl moiety composed of a 3-(3-hydroxyalkanoyloxy)alkaloid acid (HAA) and a sugar moiety composed of one or two rhamnose sugars. Rhamnolipids function as surfactants and virulence factors and are involved in biofilm formation and cell motility. The rhamnose sugar component is produced via the dTDP-L-rhamnose biosynthetic pathway which forms dTDP-L-rhamnose from glucose 6-phosphate (G6P) in five steps. First, glucose 6-phosphate is converted into glucose 1-phosphate (G1P) via the enzyme phosphoglucomutase (AlgC). Second, glucose 1-phosphate is converted into dTDP-D-glucose via the enzyme glucose-1-phosphate thymidylyltransferase (RmlA). Third, dTDP-D-glucose is converted into dTDP-4-dehydro-6-deoxy-D-glucose via the enzyme dTDP-glucose 4,6-dehydratase (RmlB). Fourth, dTDP-4-dehydro-6-deoxy-D-glucose is converted into dTDP-4-dehydro-L-rhamnose via the enzyme dTDP-4-dehydrorhamnose 3,5-epimerase (RmlC). Fifth, dTDP-4-dehydro-L-rhamnose is converted into dTDP-L-rhamnose via the enzyme dTDP-4-dehydrorhamnose reductase (RmlD). The HAA component is synthesized from 3-hydroxyacyl-[acyl-carrier protein] diverted from fatty acid biosynthesis via the enzyme 3-(3-hydroxydecanoyloxy)decanoate synthase (RhIA). The final step in rhamnolipid biosynthesis is the formation of the glycosidic link between the rhamnose sugar component and the HAA component. This is accomplished by two rhamnosyltransferases (RhlB and RhlC) which catalyze sequential glycosyl transfer reactions to first form mono-rhamnolipids (via RhIB) and then di-rhamnolipids (via RhIC). RHlA, RHlB, and RHlC are associated with the inner membrane.

Rhamnolipid Biosynthesis References