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Carotenoids

Background

Carotenoids are organic pigments naturally present in plants, algae and some bacteria. There are more than 600 carotenoids, which can be categorised into xanthophylls (hydrocarbons containing oxygen element) and carotenes (hydrocarbons containing no oxygen). Carotenoids perform a range of functions, including light energy absorption, protection against photo-damage, acting as antioxidants, and as precursor to other organic compounds. In human, for example, beta-carotene is the precursor to vitamin A.

Biochemical pathway of carotenoid synthesis

The common starting point for carotenoid synthesis is farnesyl pyrophosphate (FPP), which derives from two precursors, isopentenyl pyrophosphate (IPP) and dimethylallyl pyrophosphate (DMAPP). In general, there are two pathways for synthesising IPP and DMAPP: the Mevalonate Pathway (starting with acetyl CoA) and the Non-mevalonate Pathway (starting with pyruvate and glyceradehyde-3-phosphate). While the Mevalonate Pathway is present in all higher eukaryotes, the Non-mevalonate Pathway is present in E.coli.

Mevalonate Pathway (image adopted from Wikipedia, http://en.wikipedia.org/wiki/Mevalonate_pathway)

Non-mevalonate Pathway (image adopted from Yuan et al. 2006)

After IPP and DMAPP go on to form FPP, a series of enzymatic reactions convert the colourless FPP to coloured compounds: red lycopene and orange β-carotene.

By modulating the enzymes involved in this conversion pathway ("CrtE", "CrtB", "CrtI", and "CrtY"), we aim to produce and control different coloured pigments as signal output.