The search for new chlorophyll-binding proteins in the cyanobacterium Synechocystis sp. PCC 6803

Light harvesting provides a major challenge in the production of biofuels from microorganisms; while sunlight provides the energy necessary for biomass/biofuel production, at the same time it damages the cells. The genome of Synechocystis sp. PCC 6803 was searched for open reading frames that might code for yet unidentified chlorophyll-binding proteins with low molecular mass that could be involved in stress-adaptation. Amongst 9167 hypothetical ORFs corresponding to potential polypeptides of 100 amino acids or less, two were identified that had the potential to be pigment-binding, because they (i) encoded a potential transmembrane region, (ii) showed sequence similarity with known chlorophyll-binding domains, (iii) were conserved in other cyanobacterial species, and (iv) their codon adaptation index indicated significant translation probability. The two ORFs were located complementary (antisense) and internal to the ferrochelatase (hemH) and the pyruvate dehydrogenase (pdh) genes and therefore were named a-fch and a-pdh, respectively. Transcription of both genes was confirmed; however, no translated proteins could be detected immunologically. Whereas mutations within a-pdh or a-fch did not lead to any obvious phenotype, it is clear that transcripts and proteins over and above the currently known set may play a role in defining the physiology of cyanobacteria and other organisms.