Summary: APPLIED AND ENVIRONMENTAL MICROBIOLOGY, June 2003, p. 35733579 Vol. 69, No. 6
0099-2240/03/$08.00 0 DOI: 10.1128/AEM.69.6.35733579.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.
A C35 Carotenoid Biosynthetic Pathway
Daisuke Umeno* and Frances H. Arnold*
Division of Chemistry and Chemical Engineering, California Institute of Technology,
Pasadena, California 91125
Received 20 November 2002/Accepted 20 March 2003
Upon coexpression with Erwinia geranylgeranyldiphosphate (GGDP) synthase in Escherichia coli, C30 ca-
rotenoid synthase CrtM from Staphylococcus aureus produces novel carotenoids with the asymmetrical C35
backbone. The products of condensation of farnesyldiphosphate and GDP, C35 structures comprise 40 to 60%
of total carotenoid accumulated. Carotene desaturases and carotene cyclases from C40 or C30 pathways
accepted and converted the C35 substrate, thus creating a C35 carotenoid biosynthetic pathway in E. coli.
Directed evolution to modulate desaturase step number, together with combinatorial expression of the desatu-
rase variants with lycopene cyclases, allowed us to produce at least 10 compounds not previously described.
This result highlights the plastic and expansible nature of carotenoid pathways and illustrates how combina-
torial biosynthesis coupled with directed evolution can rapidly access diverse chemical structures.
Impressively diverse and rich in biological activity, natural
secondary metabolites comprise but a fraction of the chemicals
that could be made by biological systems. Some new metabo-