Genetically engineered biosynthetic pathways for nonnatural C carotenoids using C-elongases and C-cyclases in Escherichia coli.

While the majority of the natural carotenoid pigments are based on 40-carbon (C) skeleton, some carotenoids from bacteria have larger C skeleton, biosynthesized by attaching two isoprene units (C) to both sides of the C carotenoid pigment lycopene. Subsequent cyclization reactions result in the production of C carotenoids with diverse and unique skeletal structures. To produce even larger nonnatural novel carotenoids with C + C + C = C skeletons, we systematically coexpressed natural C carotenoid biosynthetic enzymes (lycopene C-elongases and C-cyclases) from various bacterial sources together with the laboratory-engineered nonnatural C-lycopene pathway in Escherichia coli. Among the tested enzymes, the elongases and cyclases from Micrococcus luteus exhibited significant activity toward C-lycopene, and yielded the novel carotenoids C-flavuxanthin and C-sarcinaxanthin. Moreover, coexpression of M. luteus elongase with Corynebacterium cyclase resulted in the production of C-sarcinaxanthin, C-sarprenoxanthin, and C-decaprenoxanthin.