Carotenoid diversity: a modular role for the phytoene desaturase step

Carotenoids play a crucial role in light harvesting and are essential photoprotective agents in photosynthesis. It has also been suggested that their ability to scavenge harmful radicals may offer protection against cancer and heart disease. Key enzymes in the carotenoid biosynthetic pathway of the photosynthetic bacterium Rhodobacter sphaeroides can be successfully replaced with the corresponding enzyme from the non-photosynthetic bacterium Erwinia herbicola. This results in the synthesis of carotenoids new to Rhodobacter. The response of the pathway to 'swapping' these enzymes may explain how a wide range of carotenoids can be produced with relatively minor changes to the basic biosynthetic pathway.