Plant and algal chlorophyll synthases function in Synechocystis and interact with the YidC/Alb3 membrane insertase.

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.

PufQ regulates porphyrin flux at the haem/bacteriochlorophyll branchpoint of tetrapyrrole biosynthesis via interactions with ferrochelatase.

Facultative phototrophs such as Rhodobacter sphaeroides can switch between heterotrophic and photosynthetic growth. This transition is governed by oxygen tension and involves the large-scale production of bacteriochlorophyll, which shares a biosynthetic pathway with haem up to protoporphyrin IX. Here, the pathways diverge with the insertion of Fe or Mg into protoporphyrin by ferrochelatase or magnesium chelatase, respectively.

Biosynthesis of Chlorophyll a in a Purple Bacterial Phototroph and Assembly into a Plant Chlorophyll-Protein Complex.

Improvements to photosynthetic efficiency could be achieved by manipulating pigment biosynthetic pathways of photosynthetic organisms in order to increase the spectral coverage for light absorption. The development of organisms that can produce both bacteriochlorophylls and chlorophylls is one way to achieve this aim, and accordingly we have engineered the bacteriochlorophyll-utilizing anoxygenic phototroph Rhodobacter sphaeroides to make chlorophyll a. Bacteriochlorophyll and chlorophyll share a common biosynthetic pathway up to the precursor chlorophyllide.

Elucidation of the preferred routes of C8-vinyl reduction in chlorophyll and bacteriochlorophyll biosynthesis.

Most of the chlorophylls and bacteriochlorophylls utilized for light harvesting by phototrophic organisms carry an ethyl group at the C8 position of the molecule, the product of a C8-vinyl reductase acting on a chlorophyll/bacteriochlorophyll biosynthetic precursor. Two unrelated classes of C8-vinyl reductase are known to exist, BciA and BciB, found in the purple phototroph Rhodobacter sphaeroides and the cyanobacterium Synechocystis sp. PCC6803 respectively.

A cyanobacterial chlorophyll synthase-HliD complex associates with the Ycf39 protein and the YidC/Alb3 insertase.

Macromolecular membrane assemblies of chlorophyll-protein complexes efficiently harvest and trap light energy for photosynthesis. To investigate the delivery of chlorophylls to the newly synthesized photosystem apoproteins, a terminal enzyme of chlorophyll biosynthesis, chlorophyll synthase (ChlG), was tagged in the cyanobacterium Synechocystis PCC 6803 (Synechocystis) and used as bait in pull-down experiments. We retrieved an enzymatically active complex comprising ChlG and the high-light-inducible protein HliD, which associates with the Ycf39 protein, a putative assembly factor for photosystem II, and with the YidC/Alb3 insertase.