Asymmetrically acting lycopene -cyclases (CrtLm)from non-photosynthetic bacteria

Carotenoids have important functions in photosynthesis, nutrition, and protection against oxidative damage. Some natural carotenoids are asymmetrical molecules that are difficult to produce chemically. Biological production of carotenoids using specific enzymes is a potential alternative to extraction from natural sources. Here we report the isolation of lycopene -cyclases that selectively cyclize only one end of lycopene or neurosporene. The crtLm genes encoding the asymmetrically acting lycopene -cyclases were isolated from non-photosynthetic bacteria that produced monocyclic carotenoids. Co-expression of these crtLm genes with the crtEIB genes from Pantoea stewartii (responsible for lycopene synthesis)resulted in the production of monocyclic -carotene in Escherichia coli. The asymmetric cyclization activity of CrtLm could be inhibited by the lycopene -cyclase inhibitor 2-(4-chlorophenylthio)-triethylamine (CPTA). Phylogenetic analysis suggested that bacterial CrtL-type lycopene -cyclases might represent an evolutionary link between the common bacterial CrtY-type of lycopene -cyclases and plant lycopene - and -cyclases. These lycopene -cyclases may be used for efficient production of high-value asymmetrically cyclized carotenoids.