FtsH proteases (FtsHs) belong to intramembrane ATP-dependent metalloproteases which are widely distributed in eubacteria, mitochondria and chloroplasts. The best-studied roles of FtsH in Escherichia coli include quality control of membrane proteins, regulation of response to heat shock, superoxide stress and viral infection, and control of lipopolysaccharide biosynthesis. While heterotrophic bacteria mostly contain a single indispensable FtsH complex, photosynthetic cyanobacteria usually contain three FtsH complexes: two heterocomplexes and one homocomplex. The essential cytoplasmic FtsH1/3 most probably fulfills a role similar to other bacterial FtsHs, whereas the thylakoid FtsH2/3 heterocomplex and FtsH4 homocomplex appear to maintain the photosynthetic apparatus of cyanobacteria and optimize its functionality. Moreover, recent studies suggest the involvement of all FtsH proteases in a complex response to nutrient stresses. In this review, we aim to comprehensively evaluate the functions of the cyanobacterial FtsHs specifically under stress conditions with emphasis on nutrient deficiency and high irradiance. We also point to various unresolved issues concerning FtsH functions, which deserve further attention.

• Klíčová slova
• Cyanobacteria, FtsH, Nutrient stress, Photodamage, Photosystem,
• MeSH
• bakteriální proteiny * metabolismus   genetika   MeSH
• fyziologický stres * MeSH
• proteasy závislé na ATP metabolismus   genetika   MeSH
• sinice * metabolismus   fyziologie   MeSH
• Publikační typ
• časopisecké články MeSH
• přehledy MeSH
• Názvy látek
• bakteriální proteiny * MeSH
• proteasy závislé na ATP MeSH

FtsH proteases are membrane-embedded proteolytic complexes important for protein quality control and regulation of various physiological processes in bacteria, mitochondria, and chloroplasts. Like most cyanobacteria, the model species Synechocystis sp. PCC 6803 contains four FtsH homologs, FtsH1-FtsH4. FtsH1-FtsH3 form two hetero-oligomeric complexes, FtsH1/3 and FtsH2/3, which play a pivotal role in acclimation to nutrient deficiency and photosystem II quality control, respectively. FtsH4 differs from the other three homologs by the formation of a homo-oligomeric complex, and together with Arabidopsis thaliana AtFtsH7/9 orthologs, it has been assigned to another phylogenetic group of unknown function. Our results exclude the possibility that Synechocystis FtsH4 structurally or functionally substitutes for the missing or non-functional FtsH2 subunit in the FtsH2/3 complex. Instead, we demonstrate that FtsH4 is involved in the biogenesis of photosystem II by dual regulation of high light-inducible proteins (Hlips). FtsH4 positively regulates expression of Hlips shortly after high light exposure but is also responsible for Hlip removal under conditions when their elevated levels are no longer needed. We provide experimental support for Hlips as proteolytic substrates of FtsH4. Fluorescent labeling of FtsH4 enabled us to assess its localization using advanced microscopic techniques. Results show that FtsH4 complexes are concentrated in well-defined membrane regions at the inner and outer periphery of the thylakoid system. Based on the identification of proteins that co-purified with the tagged FtsH4, we speculate that FtsH4 concentrates in special compartments in which the biogenesis of photosynthetic complexes takes place.

• Klíčová slova
• FtsH4, high light-inducible protein, photosystem II biogenesis, proteolysis, thylakoid,
• MeSH
• Arabidopsis * genetika   metabolismus   MeSH
• chloroplasty metabolismus   MeSH
• fotosystém II - proteinový komplex genetika   metabolismus   MeSH
• fylogeneze MeSH
• metaloproteasy genetika   metabolismus   MeSH
• proteasy MeSH
• proteiny huseníčku * genetika   metabolismus   MeSH
• Synechocystis * genetika   metabolismus   MeSH
• tylakoidy metabolismus   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• fotosystém II - proteinový komplex MeSH
• FtsH4 protein, Arabidopsis MeSH Prohlížeč
• metaloproteasy MeSH
• proteasy MeSH
• proteiny huseníčku * MeSH

The membrane-embedded FtsH proteases found in bacteria, chloroplasts, and mitochondria are involved in diverse cellular processes including protein quality control and regulation. The genome of the model cyanobacterium Synechocystis sp PCC 6803 encodes four FtsH homologs designated FtsH1 to FtsH4. The FtsH3 homolog is present in two hetero-oligomeric complexes: FtsH2/3, which is responsible for photosystem II quality control, and the essential FtsH1/3 complex, which helps maintain Fe homeostasis by regulating the level of the transcription factor Fur. To gain a more comprehensive insight into the physiological roles of FtsH hetero-complexes, we performed genome-wide expression profiling and global proteomic analyses of Synechocystis mutants conditionally depleted of FtsH3 or FtsH1 grown under various nutrient conditions. We show that the lack of FtsH1/3 leads to a drastic reduction in the transcriptional response to nutrient stress of not only Fur but also the Pho, NdhR, and NtcA regulons. In addition, this effect is accompanied by the accumulation of the respective transcription factors. Thus, the FtsH1/3 complex is of critical importance for acclimation to iron, phosphate, carbon, and nitrogen starvation in Synechocystis.plantcell;31/12/2912/FX1F1fx1.

• MeSH
• aklimatizace genetika   MeSH
• bakteriální proteiny genetika   metabolismus   MeSH
• dusík nedostatek   metabolismus   MeSH
• exprese genu MeSH
• fosfáty nedostatek   metabolismus   MeSH
• fosforylace MeSH
• fotosystém II - proteinový komplex chemie   genetika   metabolismus   MeSH
• metaloproteasy genetika   metabolismus   MeSH
• mutace MeSH
• proteiny vázající fosfáty genetika   metabolismus   MeSH
• proteolýza MeSH
• proteom genetika   metabolismus   MeSH
• proteomika MeSH
• regulace genové exprese u bakterií genetika   MeSH
• regulon genetika   MeSH
• represorové proteiny genetika   metabolismus   MeSH
• ribozomální proteiny genetika   metabolismus   MeSH
• Synechocystis enzymologie   metabolismus   MeSH
• transkripční faktory genetika   metabolismus   MeSH
• uhlík nedostatek   metabolismus   MeSH
• živiny nedostatek   metabolismus   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• bakteriální proteiny MeSH
• dusík MeSH
• ferric uptake regulating proteins, bacterial MeSH Prohlížeč
• fosfáty MeSH
• fotosystém II - proteinový komplex MeSH
• metaloproteasy MeSH
• proteiny vázající fosfáty MeSH
• proteom MeSH
• represorové proteiny MeSH
• ribozomální proteiny MeSH
• transkripční faktory MeSH
• uhlík MeSH

Protoporphyrinogen IX oxidase (PPO), the last enzyme that is common to both chlorophyll and heme biosynthesis pathways, catalyzes the oxidation of protoporphyrinogen IX to protoporphyrin IX. PPO has several isoforms, including the oxygen-dependent HemY and an oxygen-independent enzyme, HemG. However, most cyanobacteria encode HemJ, the least characterized PPO form. We have characterized HemJ from the cyanobacterium Synechocystis sp. PCC 6803 (Synechocystis 6803) as a bona fide PPO; HemJ down-regulation resulted in accumulation of tetrapyrrole precursors and in the depletion of chlorophyll precursors. The expression of FLAG-tagged Synechocystis 6803 HemJ protein (HemJ.f) and affinity isolation of HemJ.f under native conditions revealed that it binds heme b The most stable HemJ.f form was a dimer, and higher oligomeric forms were also observed. Using both oxygen and artificial electron acceptors, we detected no enzymatic activity with the purified HemJ.f, consistent with the hypothesis that the enzymatic mechanism for HemJ is distinct from those of other PPO isoforms. The heme absorption spectra and distant HemJ homology to several membrane oxidases indicated that the heme in HemJ is redox-active and involved in electron transfer. HemJ was conditionally complemented by another PPO, HemG from Escherichia coli. If grown photoautotrophically, the complemented strain accumulated tripropionic tetrapyrrole harderoporphyrin, suggesting a defect in enzymatic conversion of coproporphyrinogen III to protoporphyrinogen IX, catalyzed by coproporphyrinogen III oxidase (CPO). This observation supports the hypothesis that HemJ is functionally coupled with CPO and that this coupling is disrupted after replacement of HemJ by HemG.

• Klíčová slova
• HemJ, Synechocystis sp. PCC 6803, coproporphyrinogen III oxidase, cyanobacteria, enzyme purification, heme, membrane protein, photosynthesis, protoporphyrinogen IX oxidase,
• MeSH
• hem chemie   metabolismus   MeSH
• koproporfyrinogenoxidasa chemie   metabolismus   MeSH
• molekulární modely MeSH
• oxidace-redukce MeSH
• protoporfyrinogenoxidasa chemie   metabolismus   MeSH
• Synechocystis enzymologie   MeSH
• tetrapyrroly chemie   metabolismus   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• hem MeSH
• koproporfyrinogenoxidasa MeSH
• protoporfyrinogenoxidasa MeSH
• tetrapyrroly MeSH

One strategy for enhancing photosynthesis in crop plants is to improve their ability to repair photosystem II (PSII) in response to irreversible damage by light. Despite the pivotal role of thylakoid-embedded FtsH protease complexes in the selective degradation of PSII subunits during repair, little is known about the factors involved in regulating FtsH expression. Here we show using the cyanobacterium Synechocystis sp. PCC 6803 that the Psb29 subunit, originally identified as a minor component of His-tagged PSII preparations, physically interacts with FtsH complexes in vivo and is required for normal accumulation of the FtsH2/FtsH3 hetero-oligomeric complex involved in PSII repair. We show using X-ray crystallography that Psb29 from Thermosynechococcus elongatus has a unique fold consisting of a helical bundle and an extended C-terminal helix and contains a highly conserved region that might be involved in binding to FtsH. A similar interaction is likely to occur in Arabidopsis chloroplasts between the Psb29 homologue, termed THF1, and the FTSH2/FTSH5 complex. The direct involvement of Psb29/THF1 in FtsH accumulation helps explain why THF1 is a target during the hypersensitive response in plants induced by pathogen infection. Downregulating FtsH function and the PSII repair cycle via THF1 would contribute to the production of reactive oxygen species, the loss of chloroplast function and cell death.This article is part of the themed issue 'Enhancing photosynthesis in crop plants: targets for improvement'.

• Klíčová slova
• D1 subunit, Synechocystis, hypersensitive response, photoinhibition, thylakoid formation 1 gene, thylakoid membrane,
• MeSH
• Arabidopsis genetika   fyziologie   MeSH
• bakteriální proteiny genetika   metabolismus   MeSH
• chloroplasty metabolismus   MeSH
• fotosyntéza * MeSH
• fotosystém II - proteinový komplex genetika   metabolismus   MeSH
• proteiny huseníčku genetika   metabolismus   MeSH
• sinice genetika   fyziologie   MeSH
• Synechocystis genetika   fyziologie   MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• bakteriální proteiny MeSH
• fotosystém II - proteinový komplex MeSH
• proteiny huseníčku MeSH