Multiple Rieske Iron Sulfur Proteins of Photosynthesis in the Cyanobacterium Synechocystis SP PCC 6803

Photosynthesis;Cyanobacteria;Electron transfer;Iron-sulfur proteins

Ranade, Saurabh J.Kallas, Toivo ;

University of Wisconsin

关键词: Photosynthesis;    Cyanobacteria;    Electron transfer;    Iron-sulfur proteins;   

Others  :  https://minds.wisconsin.edu/bitstream/handle/1793/62210/Ranade.pdf?sequence=3&isAllowed=y

瑞士|英语

来源: University of Wisconsin

【 摘 要 】

The cytochrome bf complex is essential for both photosynthetic and respiratory electrontransport in cyanobacteria. A Rieske iron-sulfur protein (ISP) is an essential subunit ofthis complex. The cyanobacterium, Synechocystis sp. PCC 6803 carries three genes,petC1, petC2, petC3, for different forms of Rieske ISPs. PetC1 is the major ISP. Thefunctions of the PetC2 and PetC3 ISPs are not well understood. My goal was toinvestigate the roles of these Rieske proteins in electron transfer and redox signalingmediated by the cytochrome bf complex. Wild type Synechocystis and a mutant strain(PetC1) that lacks the PetC1 ISP and thus uses the PetC2 ISP in its cytochrome bfcomplex were used for these studies. These strains were grown photosyntheticallyfollowed by shifts to dark aerobic and anaerobic conditions to test the postulated role ofthe PetC2 Rieske ISP in dark metabolism. Expression of the three Rieske ISP genes andcontrol genes (psaC, for a photosystem I subunit; zwf, for glucose-6-phosphatedehydrogenase; and rpnB, for an RNAse P subunit) was investigated by reversetranscriptasequantitative polymerase chain reactions (RT-qPCR). The relative abundanceof photosystem and cytochrome bf proteins in the wild type and PetC1 mutant strainwas investigated by liquid chromatography, tandem mass spectrometry (LC-MS/MS).Electron transfer reactions were investigated by light-induced, kinetics spectroscopy togain information about relative quantities of electron transfer protein complexes andcomponents in the wild type and PetC1 strains and to compare the catalytic efficienciesof the PetC1 and PetC2 Rieske ISPs. RT-qPCR data from the wild type showed elevatedexpression of petC2 relative to petC1 during dark anaerobiosis and greatly increasedpetC2 expression, as might be expected, in the PetC1 mutant. Gene expression andother data suggests that PetC3 has a function independent of the cytochrome bf complex.Kinetics spectroscopy data suggest that the PetC1 mutant has a highly unusualcytochrome bf complex consisting primarily of the PetC2 Rieske ISP and cytochrome b6proteins. Surprisingly, the latter is kinetically coupled despite a very low content of thenormally essential cytochrome f protein. The kinetics data further indicate that the PetC1and PetC2 Rieske iron-sulfur proteins have similar catalytic efficiencies. Questionsremain as to the specific roles of the PetC2 and PetC3 Rieske proteins. Overall, theresearch contributes to understanding electron transfer pathways and mechanisms bywhich cyanobacteria adapt to changing environments. This knowledge will be importantfor engineering cyanobacterial electron transfer pathways for biofuels applications.