β-Cryptoxanthin Production in Escherichia coli by Optimization of the Cytochrome P450 CYP97H1 Activity

Cytochromes P450, forming a superfamily of monooxygenases containing heme as a cofactor, show great versatility in substrate specificity. Metabolic engineering can take advantage of this feature to unlock novel metabolic pathways. However, the cytochromes P450 often show difficulty being expressed in a heterologous chassis. As a case study in the prokaryotic host Escherichia coli, the heterologous synthesis of β-cryptoxanthin was addressed. This carotenoid intermediate is difficult to produce, as its synthesis requires a monoterminal hydroxylation of β-carotene whereas most of the classic carotene hydroxylases are dihydroxylases. This study was focused on the optimization of the in vivo activity of CYP97H1, an original P450 β-carotene monohydroxylase. Engineering the N-terminal part of CYP97H1, identifying the matching redox partners, defining the optimal cellular background and adjusting the culture and induction conditions improved the production by 400 times compared to that of the initial strain, representing 2.7 mg/L β-cryptoxanthin and 20% of the total carotenoids produced.