Proteomic comparison of HliD and Ycf39 protein abundances in FLAG-tagged chlorophyll synthase co-immunoprecipitation assays of control and CrtR/CruF (carotenoid biosynthesis) knockout strains of Synechocystis sp. PCC 6803.

Chlorophyll a synthase (ChlG) is the enzyme responsible for attaching either a geranygeranyl or phytyl group to the chlorophyllide macrocycle during chlorophyll biosynthesis. Previous co-immunoprecipitation assays using FLAG-tagged ChlG identified the high light inducible protein HliD and the photosystem II assembly factor Ycf39 among the interaction partners. Non-protein components of this complex are the carotenoids zeaxanthin and myxoxanthophyll. To elucidate the function of these carotenoids in the association of ChlG/HliD/Ycf39, knockout strains of Synechocystis were produced to disrupt carotenoid biosynthesis. The abundances of HliD and Ycf39 relative to FLAG-tagged ChlG were compared in the different strains by proteomic analysis.