Construction of carotenoid biosynthetic pathways using squalene synthase

•Squalene synthase and carotenoid desaturase CrtN produced carotenoid pigments.•Various experiments suggested CrtN desaturates squalene into dehydrosqualene.•Possible existence of “squalene/lycopersene-to-carotenoid route” was suggested.•A new method of color screening for squalene synthase activity was proposed. The first committed steps of steroid/hopanoid pathways involve squalene synthase (SQS). Here, we report the Escherichia coli production of diaponeurosporene and diapolycopene, yellow C30 carotenoid pigments, by expressing human SQS and Staphylococcus aureus dehydrosqualene (C30 carotenoid) desaturase (CrtN). We suggest that the carotenoid pigments are synthesized mainly via the desaturation of squalene rather than the direct synthesis of dehydrosqualene through the non-reductive condensation of prenyl diphosphate precursors, indicating the possible existence of a “squalene route” and a “lycopersene route” for C30 and C40 carotenoids, respectively. Additionally, this finding yields a new method of colorimetric screening for the cellular activity of squalene synthases, which are major targets for cholesterol-lowering drugs.