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 similar to4.4%, On the basis of these results, the evolution of pigment systems in an early stage of cyanobacterial development is discussed in this paper.