title: Two essential FtsH proteases control the level of the Fur repressor during iron deficiency in the cyanobacterium Synechocystis sp. PCC 6803.
abstract: The cyanobacterium Synechocystis sp. PCC 6803 expresses four different FtsH protease subunits (FtsH1-4) that assemble into specific homo- and heterocomplexes. The FtsH2/FtsH3 complex is involved in photoprotection but the physiological roles of the other complexes, notably the essential FtsH1/FtsH3 complex, remain unclear. Here we show that the FtsH1 and FtsH3 proteases are involved in the acclimation of cells to iron deficiency. A mutant conditionally depleted in FtsH3 was unable to induce normal expression of the IsiA chlorophyll-protein and FutA1 iron transporter upon iron deficiency due to a block in transcription, which is regulated by the Fur transcriptional repressor. Levels of Fur declined in the WT and the FtsH2 null mutant upon iron depletion but not in the FtsH3 downregulated strain. A similar stabilizing effect on Fur was also observed in a mutant conditionally depleted in the FtsH1 subunit. Moreover, a mutant overexpressing FtsH1 showed reduced levels of Fur and enhanced accumulation of both IsiA and FutA1 even under iron sufficiency. Analysis of GFP-tagged derivatives and biochemical fractionation supported a common location for FtsH1 and FtsH3 in the cytoplasmic membrane. Overall we propose that degradation of the Fur repressor mediated by the FtsH1/FtsH3 heterocomplex is critical for acclimation to iron depletion.
authors.affiliation: Institute of Microbiology, Academy of Sciences, Opatovický mlýn, 37981, Třeboň, Czech Republic; Faculty of Science, University of South Bohemia, Branišovská 31, 370 05, České Budějovice, Czech Republic.
authors.forename: Vendula
authors.initials: V
authors.lastname: Krynická
authors.forename: Martin
authors.initials: M
authors.lastname: Tichý
authors.forename: Jaroslav
authors.initials: J
authors.lastname: Krafl
authors.forename: Jianfeng
authors.initials: J
authors.lastname: Yu
authors.forename: Radek
authors.initials: R
authors.lastname: Kaňa
authors.forename: Marko
authors.initials: M
authors.lastname: Boehm
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Nixon
authors.forename: Josef
authors.initials: J
authors.lastname: Komenda
mesh_terms: D049069:ATP-Dependent Proteases / Q000378:metabolism*; D000222:Adaptation, Physiological; D001426:Bacterial Proteins / Q000378:metabolism*; D002462:Cell Membrane / Q000201:enzymology; D015964:Gene Expression Regulation, Bacterial; D007501:Iron / Q000378:metabolism*; D012097:Repressor Proteins / Q000378:metabolism*; D046939:Synechocystis / Q000201:enzymology* / Q000235:genetics* / Q000502:physiology
chemical_list: D001426:Bacterial Proteins; D012097:Repressor Proteins; C068477:ferric uptake regulating proteins, bacterial; D007501:Iron; D049069:ATP-Dependent Proteases