In Vitro Biosynthesis of Violacein from l-Tryptophan by the Enzymes VioA−E from Chromobacterium violaceum

The purple chromobacterial pigment violacein arises by enzymatic oxidation and coupling of two molecules of l-tryptophan to give a rearranged pyrrolidone-containing scaffold in the final pigment. We have purified five contiguously encoded proteins VioA−E after expression in Escherichia coli and demonstrate the full 14-electron oxidation pathway to yield the final chromophore. The flavoenzyme VioA and the heme protein VioB work in conjunction to oxidize and dimerize l-tryptophan to a nascent product that can default to the off pathway metabolite chromopyrrolic acid. In the presence of VioE, the intermediate instead undergoes on-pathway [1,2] indole rearrangement to prodeoxyviolacein. The last two enzymes in the pathway are flavin-dependent oxygenases, VioC and VioD, that act sequentially. VioD hydroxylates one indole ring at the 5-position to yield proviolacein, and VioC then acts on the other indole ring at the 2-position to create the oxindole and complete violacein formation.