Geranyl modification on the tryptophan residue of ComXRO-E-2 pheromone by a cell-free system

► ComX pheromone has prenylated tryptophan residue. ► Universality of this unique modification has not been elucidated. ► We established a cell-free system, whereby the tryptophan residue is geranylated. ► Using a cell-free system, we investigated enzymatic reaction conditions. ► This is the first report of in vitro geranylation on the tryptophan residue.