Identification Of An NADPH Dehydrogenase Active Super-complex In The Cyanobacterium Synechocystis Sp. Strain PCC 6803 And Its Regulation And Function

Cyanobacteria possess functionally distinct multiple NADPH dehydrogenase (NDH-1)complexes that are essential to respiration, photosystem I-dependent cyclic electron transportand COB2B-uptake. Recently, we found that the activity of NDH-1 was strongly changed duringthe growth phase of cells, and was highest in cells at a logarithmic phase of the growth.Therefore, we used the cells at logarithmic phase and succeeded in identifying active NDH-1complexes. Staining of gels for NADPH-nitroblue tetrazolium (NBT) oxidoreductase activityafter native-PAGE of thylakoid membrane solubilized with n-dodecyl-?-maltoside andimmunoblotting demonstrated the presence of two active NDH-1 complexes, Act-NDH-1Sup(UActUive USupUer-complex; 1,000 kDa) and Act-NDH-1M (UActUive UMUedium-complex; 380 kDa),in Synechocystis sp. strain PCC 6803. The activity of Act-NDH-1Sup is much higher thanthat of Act-NDH-1M on a NDH-1 enzyme protein basis. Act-NDH-1Sup and Act-NDH-1Mappear to be NDH-1L dimer and NDH-1M, respectively, with subunits essential for theactivity.Our studies showed that the enzyme activity of Act-NDH-1Sup was suppressed but that ofAct-NDH-1M was enhanced by low COB2B (i.e., cells grown in air) and that the expression andactivity of Act-NDH-1Sup were down-regulated but those of Act-NDH-1M not siginificantlyaffected by exogonous glucose, revealing the different reponses of the two active complexesof NDH-1 to changing environmental factors. In addition, the expression and activity ofAct-NDH-1Sup were markedly down-regulated (up-regulated) by supplementing exogenousGlucose (DCMU) in BG-11 medium, resulting in a(n) reduction (oxidation) of plastoquinone pool. This indicates that the changes in expression and activity of Act-NDH-1Sup are under aredox control of PQ pool. To our knowledge, the redox control of active NDH-1 complex(es)in cyanobacteria is first revealed in this study.Analysis of various mutants for their physiological properties in relation to the presence orabsence of Act-NDH-1Sup and Act-NDH-1M indicated that Act-NDH-1Sup is essential forrespiration and photosystem I-dependent cyclic electron transport, while Act-NDH-1M isinvolved in high affinity COB2B-uptake. In addition, phycobilisomes (PBS) are the majoraccessory light-harvesting complexes in cyanobacteria and their mobility affects the lightenergy distribution between the two photosystems. We showed that the movement of PBSfrom photosystem II (I) to photosystem I (II) caused the increase (decrease) in photosystemI-dependent cyclic electron transport, and decrease (increase) in respiration. We also foundthat the presence of Act-NDH-1Sup in cells of Synechocystis 6803 is essential for survival ofcell under weak light (2-5μEmP-2PsP-1P). However, little is known regarding how Act-NDH-1Supto affect the survival of cell under such light conditions.