Molecular cloning and functional expression in E. coli of a novel plant enzyme mediating ξ-carotene desaturation

AbstractWe have cloned a cDNA from the plant Capsicum annuum which encodes a novel enzyme mediating the dehydrogenation of ξ-carotene and neurosporene to lycopene when expressed in E. coli cells accumulating ξ-carotene or neurosporene. This enzyme is unable to dehydrogenate either phytoene or lycopene. The deduced amino acid sequence suggests that this cDNA encodes a polypeptide whose mature size is ca. 59 kDa and which is synthesized as a precursor with a NH2-terminal extension resembling transit peptides for plastid targeting. Sequence comparison reveals 33–35% similarity with previously cloned plant or cyanobacterial phytoene desaturases. In contrast, only limited sequence similarity is found with a ξ-carotene desaturase from the cyanobacterium Anabaena