Abstract
In the model cyanobacterium Synechocystis sp. PCC 6803, the terminal enzyme of chlorophyll biosynthesis, chlorophyll synthase (ChlG), forms a complex with high light‐inducible proteins, the photosystem II assembly factor Ycf39 and the YidC/Alb3/OxaI membrane insertase, co‐ordinating chlorophyll delivery with cotranslational insertion of nascent photosystem polypeptides into the membrane. To gain insight into the ubiquity of this assembly complex in higher photosynthetic organisms, we produced functional foreign chlorophyll synthases in a cyanobacterial host. Synthesis of algal and plant chlorophyll synthases allowed deletion of the otherwise essential native cyanobacterial gene. Analysis of purified protein complexes shows that the interaction with YidC is maintained for both eukaryotic enzymes, indicating that a ChlG‐YidC/Alb3 complex may be evolutionarily conserved in algae and plants.
Highlights
IntroductionPCC 6803, the terminal enzyme of chlorophyll biosynthesis, chlorophyll synthase (ChlG), forms a complex with high light-inducible proteins, the photosystem II assembly factor Ycf and the YidC/Alb3/OxaI membrane insertase, co-ordinating chlorophyll delivery with cotranslational insertion of nascent photosystem polypeptides into the membrane
To investigate whether chlorophyll synthase (ChlG) proteins from algae and higher plants are functional in a cyanobacterial system, and if interactions between foreign ChlGs and the cyanobacterial high light-inducible protein D (HliD), Ycf39 and YidC proteins are maintained, a collection of mutant strains was generated in which foreign chlG genes encoding N-terminally 3xFLAG-tagged proteins were added in trans to Synechocystis (Table 1)
The processes of chlorophyll biosynthesis and photosystem assembly in phototrophic organisms appear to be co-ordinated, ensuring efficient channelling of newly produced chlorophyll pigments to de novo photosystem polypeptides to enable their cotranslational insertion into the thylakoid membrane and assembly into functioning photosystems [27,28]
Summary
PCC 6803, the terminal enzyme of chlorophyll biosynthesis, chlorophyll synthase (ChlG), forms a complex with high light-inducible proteins, the photosystem II assembly factor Ycf and the YidC/Alb3/OxaI membrane insertase, co-ordinating chlorophyll delivery with cotranslational insertion of nascent photosystem polypeptides into the membrane. Solar energy is absorbed by chlorophyll situated in membrane intrinsic photosystems and used for charge separation, which drives ATP and NADPH production The structures of these photosystems show chlorophyll molecules in specific arrangements allowing highly efficient light capture and energy transfer [1,2,3,4]. Chidgey et al [7] investigated handover of chlorophyll from ChlG to nascent light-harvesting polypeptides in the model cyanobacterium Synechocystis sp.
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