Involvement of the HtrA family of proteases in the protection of the cyanobacterium
            <i>Synechocystis</i>
            PCC 6803 from light stress and in the repair of photosystem II

Silva, Paulo; Choi, Young‐Jun; Hassan, Hanadi A. G.; Nixon, Peter J.

doi:10.1098/rstb.2002.1146

Cited by 30 publications

(33 citation statements)

References 41 publications

(46 reference statements)

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“…Therefore, the use of DegP2 in D1 degradation in chloroplasts might have occurred after the divergence of cyanobacteria and chloroplasts. The contribution of the DegP/ HtrA proteases found in Synechocystis to D1 degradation in vivo is unclear, although it is known that they are needed for growth at high light intensities (Silva et al, 2002). However, the dramatic phenotype of the slr0228 mutant described here suggests an important physiological role for this particular FtsH protease in the degradation of damaged D1.…”

Section: Are Multiple Proteases Involved In D1 Degradation In Synechomentioning

confidence: 70%

FtsH Is Involved in the Early Stages of Repair of Photosystem II inSynechocystissp PCC 6803 [W]

et al. 2003

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When plants, algae, and cyanobacteria are exposed to excessive light, especially in combination with other environmental stress conditions such as extreme temperatures, their photosynthetic performance declines. A major cause of this photoinhibition is the light-induced irreversible photodamage to the photosystem II (PSII) complex responsible for photosynthetic oxygen evolution. A repair cycle operates to selectively replace a damaged D1 subunit within PSII with a newly synthesized copy followed by the light-driven reactivation of the complex. Net loss of PSII activity occurs (photoinhibition) when the rate of damage exceeds the rate of repair. The identities of the chaperones and proteases involved in the replacement of D1 in vivo remain uncertain. Here, we show that one of the four members of the FtsH family of proteases (cyanobase designation slr0228) found in the cyanobacterium Synechocystis sp PCC 6803 is important for the repair of PSII and is vital for preventing chronic photoinhibition. Therefore, the ftsH gene family is not functionally redundant with respect to the repair of PSII in this organism. Our data also indicate that FtsH binds directly to PSII, is involved in the early steps of D1 degradation, and is not restricted to the removal of D1 fragments. These results, together with the recent analysis of ftsH mutants of Arabidopsis, highlight the critical role played by FtsH proteases in the removal of damaged D1 from the membrane and the maintenance of PSII activity in vivo.

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Section: Are Multiple Proteases Involved In D1 Degradation In Synechomentioning

confidence: 70%

FtsH Is Involved in the Early Stages of Repair of Photosystem II inSynechocystissp PCC 6803 [W]

et al. 2003

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“…Triple mutants of Synechocystis sp. strain PCC 6803 in which all three Deg proteases were inactivated exhibited a dramatic growth defect when they were exposed to high temperatures or high light intensities (3,39). Based on these studies, it was proposed that Synechocystis sp.…”

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confidence: 99%

“…In prokaryotes, Deg proteases are usually located in the periplasm and are implicated in the response to a variety of stresses, such as heat (3,30,33), oxidative stress (3,47), and high-light stress (3,39). Deg proteases are also essential for virulence in several pathogenic bacteria (33,47).…”

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confidence: 99%

The Serine Protease HhoA from Synechocystis sp. Strain PCC 6803: Substrate Specificity and Formation of a Hexameric Complex Are Regulated by the PDZ Domain

2007

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Enzymes of the ATP-independent Deg serine endopeptidase family are very flexible with regard to their substrate specificity. Some family members cleave only one substrate, while others act as general proteases on unfolded substrates. The proteolytic activity of Deg proteases is regulated by PDZ protein interaction domains. Here we characterized the HhoA protease from Synechocystis sp. strain PCC 6803 in vitro using several recombinant protein constructs. The proteolytic activity of HhoA was found to increase with temperature and basic pH and was stimulated by the addition of Mg 2؉ or Ca 2؉ . We found that the single PDZ domain of HhoA played a critical role in regulating protease activity and in the assembly of a hexameric complex. Deletion of the PDZ domain strongly reduced proteolysis of a sterically challenging resorufin-labeled casein substrate, but unlabeled ␤-casein was still degraded. Reconstitution of the purified HhoA with total membrane proteins isolated from Synechocystis sp. wild-type strain PCC 6803 and a ⌬hhoA mutant resulted in specific degradation of selected proteins at elevated temperatures. We concluded that a single PDZ domain of HhoA plays a critical role in defining the protease activity and oligomerization state, combining the functions that are attributed to two PDZ domains in the homologous DegP protease from Escherichia coli. Based on this first enzymatic study of a Deg protease from cyanobacteria, we propose a general role for HhoA in the quality control of extracytoplasmic proteins, including membrane proteins, in Synechocystis sp. strain PCC 6803.Proteolysis is an essential process in every living cell and is involved in protein quality control (45), as well as in regulation of diverse cellular events (11). In the cyanobacterium Synechocystis sp. strain PCC 6803, which is a widely used model system for studying photosynthesis and acclimation to abiotic stresses, 77 proteases are encoded in the genome (http://merops.sanger .ac.uk/). Three genes encode ATP-independent serine endopeptidases belonging to the Deg (HtrA) family (14,19,21,40). The protease domain of these enzymes harbors the hallmark catalytic triad consisting of His, Asp, and Ser responsible for the proteolytic activity and may additionally confer a chaperone function (16,42). Deg proteases usually contain one or two protein-protein interaction domains of the PDZ type C terminal of the protease domain (7). Studies of Escherichia coli DegP (also designated HtrA), E. coli DegS (also designated HhoB), and human HtrA2 showed that PDZ domains regulate the proteolytic activity (16,18,27,38,42,46), are involved in the formation of homooligomeric complexes (16,18,38), and play a role in substrate recognition (7,16,23,35).In prokaryotes, Deg proteases are usually located in the periplasm and are implicated in the response to a variety of stresses, such as heat (3, 30, 33), oxidative stress (3, 47), and high-light stress (3, 39). Deg proteases are also essential for virulence in several pathogenic bacteria (33,47). An intriguing fea...

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“…1) bind to the upstream region of the gene. After ROS-mediated conformational changes in the D1 protein and proteolytic degradation, the breakdown products are possibly made accessible to DNA or released by the FtsH protease into the cytoplasm (14,19,23), where they contact the DNA attached to the thylakoid membrane. The occurrence of a 25-kDa soluble D1 degradation product, possibly fragment B4, has been demonstrated in the present paper (Fig.…”

Section: Discussionmentioning

confidence: 99%

Specific Binding of D1 Protein Degradation Products to the psbAI Promoter in Synechococcus sp. Strain PCC 7942

Stelljes

Koenig

2007

J Bacteriol

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The D1:1 protein and its potentially occurring degradation products were overexpressed in Escherichia coli. Protein-DNA interaction is shown for the promoter region of psbAI. The D1:1 degradation products may be involved in transcription regulation of psbAI by binding in the promoter region. Additionally, C-terminal fragments of the D1 protein bind to a sequence with similarity to isiB, a gene which encodes a flavodoxin-like protein.Oxygenic photosynthesis is the energy conversion mechanism in cyanobacteria, algae, and plants. The light-driven processes in the thylakoid membrane require two photosystems, which are linked in series. Photosystem II (PS II) is the place of water splitting and, thus, oxygen evolution. The integral components of PS II reaction centers are the D1 and D2 proteins, which carry the cofactors of charge separation. In the unicellular cyanobacterium Synechococcus sp. strain PCC 7942, the D1 protein is encoded by a gene family of three psbA genes (8). The transcription of the psbA genes is light dependent. Under low-light conditions, the main transcript is psbAI, encoding the D1:1 form of the protein. psbAII and psbAIII are transcribed under high-light conditions and encode the D1:2 form (7, 15). The two D1 forms differ at 25 amino acid residues. Intact D1 and D2 are required for charge separation and electron transport in PS II. Because of oxygen evolution at PS II, the D1 and D2 proteins are targets of reactive oxygen species (ROS). ROS are responsible for carbonylation of protein side chains (21,22,25). This was also shown for the D1 protein (26). ROS-induced modification of the proteins may lead to a high turnover rate of the reaction center proteins. D1 breakdown products were previously shown for cyanobacterial thylakoid membranes (13). In the case of cyanobacterial D1, according to the model of Nixon and coworkers (19), FtsH is responsible for the initial degradation steps (19,24). Protein cleavage by FtsH can occur from both the N and the C termini (4, 30). After proteolysis of D1, the breakdown products are translocated through the central pore of the hexameric FtsH holoenzyme in an ATP-driven process from PS II into the cytoplasm (19). Since the catalytic Zn 2ϩ binding site of FtsH is exposed on the stromal side of the thylakoid membrane, proteolysis at the N terminus of the D1 protein is probable (19). Kihara and coworkers have shown the dislocation of membrane proteins in FtsH-mediated proteolysis (14).Additionally, there is a proteolytic event in the Q B -binding pocket between helices D and E (13). These two possible endoproteolytic steps result in five potential degradation products, which are released from the membrane, probably by FtsH, into the cyanobacterial cytoplasm. As mentioned above, transcription of the three psbA genes in Synechococcus strain PCC 7942 is regulated by light. Promoter analysis showed that the psbAI promoter is one of the strongest in Synechococcus strain PCC 7942 and contains an unusual Ϫ10 element (18). The smallest fragment, promoting the transcript...

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Involvement of the HtrA family of proteases in the protection of the cyanobacterium Synechocystis PCC 6803 from light stress and in the repair of photosystem II

Cited by 30 publications

References 41 publications

FtsH Is Involved in the Early Stages of Repair of Photosystem II inSynechocystissp PCC 6803 [W]

FtsH Is Involved in the Early Stages of Repair of Photosystem II inSynechocystissp PCC 6803 [W]

The Serine Protease HhoA from Synechocystis sp. Strain PCC 6803: Substrate Specificity and Formation of a Hexameric Complex Are Regulated by the PDZ Domain

Specific Binding of D1 Protein Degradation Products to the psbAI Promoter in Synechococcus sp. Strain PCC 7942

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