Chlorophylls are essential cofactors for photosynthesis, which sustains global food chains and oxygen production. Billions of tons of chlorophylls are synthesized annually, yet full understanding of chlorophyll biosynthesis has been hindered by the lack of characterization of the Mg–protoporphyrin IX monomethyl ester oxidative cyclase step, responsible for the distinctive green colour of these pigments. We demonstrate cyclase activity using heterologously expressed enzyme. Next, we assemble a genetic module that encodes the complete chlorophyll biosynthetic pathway and show that it functions in Escherichia coli, converting endogenous protoporphyrin IX into chlorophyll a and turning E. coli cells green. Our results delineate a minimum set of enzymes required to make chlorophyll .
As an illustration of chlorophyll function, we studied the bacteriochlorophyll b-based reaction centre light-harvesting 1 (RC-LH1) complex from the phototrophic bacterium Blastochloris viridis. The cryo-EM structure of this complex at 2.9 Å resolution reveals the structural basis for absorption of infrared light, and the molecular mechanism of quinone migration across the LH1 complex .
 Chen, G.E., Canniffe, D.P., Barnett, S.F.H., Hollingshead, S., Brindley, A.A., Vasilev, C., Bryant, D.A. and Hunter, C.N. (2018) Complete enzyme set for chlorophyll biosynthesis in Escherichia coli. Science Advances 4, eaaq1407.
 Qian, P., Siebert, C.A., Wang, P., Canniffe, D.P. and Hunter, C.N. (2018) Cryo-EM structure of the Blastochloris viridis RC-LH1 complex at 2.9 Å. Nature 556, 203-208.