Chlorophyll b expressed in Cyanobacteria functions as a light-harvesting antenna in photosystem I through flexibility of the proteins.
Photosynthetic pigments bind to their specific proteins to form pigment-protein complexes. To investigate the pigment-binding activities of the proteins, chlorophyll b was for introduced the first time to a cyanobacterium that did not synthesize that pigment, and expression of its function in the native pigment-protein complex of cyanobacterium was confirmed by energy transfer. Arabidopsis CAO (chlorophyll a oxygenase) cDNA was introduced into the genome of Synechocystis sp. PCC6803. The transformant cells accumulated chlorophyll b, with the chlorophyll b content being in the range of 1.4 to 10.6% of the total chlorophyll depending on the growth phase. Polyacrylamide gel electrophoresis analysis of the chlorophyll-protein complexes of transformant cells showed that chlorophyll b was incorporated preferentially into the P700-chlorophyll a-protein complex (CP1). Furthermore, chlorophyll b in CP1 transferred light energy to chlorophyll a, indicating a functional transformation. We also found that CP1 of Chlamydomonas reinhardtii, believed to be a chlorophyll a protein, bound chlorophyll b with a chlorophyll b content of approximately 4.4%. On the basis of these results, the evolution of pigment systems in an early stage of cyanobacterial development is discussed in this paper.
Satoh
S
S
Institute of Low Temperature Science, Hokkaido University, Sapporo 060-0819, Japan.
Ikeuchi
M
M
Mimuro
M
M
Tanaka
A
A
D000818:Animals; D016825:Chlamydomonas reinhardtii / Q000378:metabolism; D002734:Chlorophyll / Q000235:genetics / Q000378:metabolism*; D000458:Cyanobacteria / Q000235:genetics / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial; D015971:Gene Expression Regulation, Enzymologic; D010105:Oxygenases / Q000235:genetics; D045322:Photosynthetic Reaction Center Complex Proteins / Q000378:metabolism*
D045322:Photosynthetic Reaction Center Complex Proteins; D002734:Chlorophyll; C037184:chlorophyll b; D010105:Oxygenases; C115272:chlorophyll a oxygenase