pH-regulated chaperone function of cyanobacterial Hsp90 and Hsp70: implications for light/dark regulation.

We have shown that cyanobacterial chaperonins have pH-dependent anti-aggregation activity. The pH in cyanobacterial cytosol increases by one pH unit following a shift from darkness to light. In this study, we examined whether other major chaperones such as Hsp90 (HtpG) and Hsp70 (DnaK2) from the cyanobacterium Synechococcus elongatus PCC 7942 also display pH-dependent activity.

A cyclic lipopeptide surfactin is a species-selective Hsp90 inhibitor that suppresses cyanobacterial growth.

Heat shock protein 90 (Hsp90) is essential for eukaryotic cells, whereas bacterial homologs play a role under stresses and in pathogenesis. Identifying species-specific Hsp90 inhibitors is challenging because Hsp90 is evolutionarily conserved. We found that a cyclic lipopeptide surfactin inhibits the ATPase activity of Hsp90 from the cyanobacterium Synechococcus elongatus (S.

pH-mediated control of anti-aggregation activities of cyanobacterial and E. coli chaperonin GroELs.

In contrast to Escherichia coli, cyanobacteria have multiple GroELs, the bacterial homologues of chaperonin/Hsp60. We have shown that cyanobacterial GroELs are mutually distinct and different from E. coli GroEL with which the paradigm for chaperonin structure/function has been established.

Regulation of the groESL1 transcription by the HrcA repressor and a novel transcription factor Orf7.5 in the cyanobacterium Synechococcus elongatus PCC7942.

The CIRCE/HrcA system is highly conserved in cyanobacterial genomes. We have shown that heat-shock induction of the groESL1 operon in the cyanobacterium Synechocystis sp. PCC6803 is negatively regulated by the CIRCE/HrcA system.

Evaluation of Open Reduction and Internal Fixation of Mandibular Condyle Fracture by Intraoperative Cone-Beam Computed Tomography in a Hybrid Operating Room.

Condylar fractures are the most common fractures of the mandible, and treatment of mandibular condylar fractures by maxillofacial surgeons is a very important procedure. However, the surgical approaches have anatomical limitations. Therefore, it is difficult to evaluate the reduction achieved in open reduction and internal fixation because of the uncertainty in securing a sufficient operative field.

Stimulation of the ATPase activity of Hsp90 by zerumbone modification of its cysteine residues destabilizes its clients and causes cytotoxicity.

Hsp90 is an ATP-dependent molecular chaperone that assists folding and conformational maturation/maintenance of many proteins. It is a potential cancer drug target because it chaperones oncoproteins. A prokaryotic homolog of Hsp90 (HtpG) is essential for thermo-tolerance in some bacteria and virulence of zoonotic pathogens.

Non-housekeeping, non-essential GroEL (chaperonin) has acquired novel structure and function beneficial under stress in cyanobacteria.

GroELs which are prokaryotic members of the chaperonin (Cpn)/Hsp60 family are molecular chaperones of which Escherichia coli GroEL is a model for subsequent research. The majority of bacterial species including E. coli and Bacillus subtilis have only one essential groEL gene that forms an operon with the co-chaperone groES gene.

Goniothalamin enhances the ATPase activity of the molecular chaperone Hsp90 but inhibits its chaperone activity.

Hsp90 is an ATP-dependent molecular chaperone that is involved in important cellular pathways such as signal transduction pathways. It is a potential cancer drug target because it plays a critical role for stabilization and activation of oncoproteins. Thus, small molecule compounds that control the Hsp90 function are useful to elucidate potential lead compounds against cancer.

Physical interaction between bacterial heat shock protein (Hsp) 90 and Hsp70 chaperones mediates their cooperative action to refold denatured proteins.

In eukaryotes, heat shock protein 90 (Hsp90) is an essential ATP-dependent molecular chaperone that associates with numerous client proteins. HtpG, a prokaryotic homolog of Hsp90, is essential for thermotolerance in cyanobacteria, and in vitro it suppresses the aggregation of denatured proteins efficiently. Understanding how the non-native client proteins bound to HtpG refold is of central importance to comprehend the essential role of HtpG under stress.

The therapeutic target Hsp90 and cancer hallmarks.

Hsp90 is a major molecular chaperone that is expressed abundantly and plays a pivotal role in assisting correct folding and functionality of its client proteins in cells. The Hsp90 client proteins include a wide variety of signal transducing molecules such as protein kinases and steroid hormone receptors. Cancer is a complex disease, but most types of human cancer share common hallmarks, including self-sufficiency in growth signals, insensitivity to growth-inhibitory mechanism, evasion of programmed cell death, limitless replicative potential, sustained angiogenesis, and tissue invasion and metastasis.

Heat shock response in photosynthetic organisms: membrane and lipid connections.

The ability of photosynthetic organisms to adapt to increases in environmental temperatures is becoming more important with climate change. Heat stress is known to induce heat-shock proteins (HSPs) many of which act as chaperones. Traditionally, it has been thought that protein denaturation acts as a trigger for HSP induction.

Cyclic lipopeptide antibiotics bind to the N-terminal domain of the prokaryotic Hsp90 to inhibit the chaperone activity.

Chemical arrays were employed to screen ligands for HtpG, the prokaryotic homologue of Hsp (heat-shock protein) 90. We found that colistins and the closely related polymyxin B interact physically with HtpG. They bind to the N-terminal domain of HtpG specifically without affecting its ATPase activity.

Comparative biochemical characterization of two GroEL homologs from the cyanobacterium Synechococcus elongatus PCC 7942.

Unlike Escherichia coli, cyanobacteria generally contain two GroEL homologs. The chaperone function of cyanobacterial GroELs was examined in vitro for the first time with GroEL1 and GroEL2 of Synechococcus elongatus PCC 7942. Both GroELs prevented aggregation of heat-denatured proteins.

HtpG, the prokaryotic homologue of Hsp90, stabilizes a phycobilisome protein in the cyanobacterium Synechococcus elongatus PCC 7942.

HtpG, a homologue of HSP90, is essential for thermotolerance in cyanobacteria. It is not known how it plays this important role. We obtained evidence that HtpG interacts with linker polypeptides of phycobilisome in the cyanobacterium Synechococcus elongatus PCC 7942.

The NADPH thioredoxin reductase C functions as an electron donor to 2-Cys peroxiredoxin in a thermophilic cyanobacterium Thermosynechococcus elongatus BP-1.

An NADPH thioredoxin reductase C was co-purified with a 2-Cys peroxiredoxin by the combination of anion exchange chromatography and electroelution from gel slices after native PAGE from a thermophilic cyanobacterium Thermosynechococcus elongatus as an NAD(P)H oxidase complex induced by oxidative stress. The result provided a strong evidence that the NADPH thioredoxin reductase C interacts with the 2-Cys peroxiredoxin in vivo. An in vitro reconstitution assay with purified recombinant proteins revealed that both proteins were essential for an NADPH-dependent reduction of H2O2.

A small heat-shock protein confers stress tolerance and stabilizes thylakoid membrane proteins in cyanobacteria under oxidative stress.

Small heat-shock proteins are molecular chaperones that bind and prevent aggregation of nonnative proteins. They also associate with membranes. In this study, we show that the small heat-shock protein HspA plays a protective role under oxidative stress in the cyanobacterium Synechococcus elongatus strain ECT16-1, which constitutively expresses HspA.

Expression and function of a groEL paralog in the thermophilic cyanobacterium Thermosynechococcus elongatus under heat and cold stress.

Cyanobacterial genomes generally contain two groEL genes, referred to as groEL1 and groEL2. The purpose of this study is to elucidate a role of groEL2 in the adaptation of the thermophilic cyanobacterium Thermosynechococcuselongatus to hot environments. Both groEL genes were found to be heat-induced, while only groEL2 was greatly cold-induced.

Interaction of the molecular chaperone HtpG with uroporphyrinogen decarboxylase in the cyanobacterium Synechococcus elongatus PCC 7942.

Uroporphyrinogen decarboxylase (HemE) is important due to its location at the first branch-point in tetrapyrrole biosynthesis. We detected a complex formation between full-length polypeptides of HtpG and HemE by biochemical studies in vivo and in vitro. The interaction suppressed the enzyme activity, suggesting a regulatory role of HtpG in tetrapyrrole biosynthesis.

Membrane regulation of the stress response from prokaryotic models to mammalian cells.

"Membrane regulation" of stress responses in various systems is widely studied. In poikilotherms, membrane rigidification could be the first reaction to cold perception: reducing membrane fluidity of membranes at physiological temperatures is coupled with enhanced cold inducibility of a number of genes, including desaturases (see J.L.

A novel light- and heat-responsive regulation of the groE transcription in the absence of HrcA or CIRCE in cyanobacteria.

The inactivation of the hrcA gene resulted in de-repression of the two CIRCE-containing groE genes in a cyanobacterium Synechocystis sp. strain PCC6803, indicating that the CIRCE operator/HrcA repressor system operates in the cyanobacterium. We found that the groE expression in the hrcA mutant is greatly induced by heat and/or light.

Studies on the role of HtpG in the tetrapyrrole biosynthesis pathway of the cyanobacterium Synechococcus elongatus PCC 7942.

In cyanobacterium Synechococcus elongatus PCC 7942, we observed that htpG-overexpression caused remarkable growth inhibition. In addition, subcellular fractionation experiments showed that HtpG was localized in the membrane fraction. To understand its function in cyanobacteria, we carried out yeast two-hybrid screening to identify specific proteins interacting with HtpG, and found out, HemE, uroporphyrinogen decarboxylase.

Photoinduced hydrogen production by direct electron transfer from photosystem I cross-linked with cytochrome c3 to [NiFe]-hydrogenase.

The photosynthetic reaction center is an efficient molecular device for the conversion of light energy to chemical energy. In a previous study, we synthesized the hydrogenase/photosystem I (PSI) complex, in which Ralstonia hydrogenase was linked to the cytoplasmic side of Synechocystis PSI, to modify PSI so that it photoproduced molecular hydrogen (H2). In that study, hydrogenase was fused with a PSI subunit, PsaE, and the resulting hydrogenase-PsaE fusion protein was self-assembled with PsaE-free PSI to give the hydrogenase/PSI complex.

Interaction of a small heat shock protein with light-harvesting cyanobacterial phycocyanins under stress conditions.

Phycobiliproteins such as phycocyanins are the most abundant proteins found in cyanobacteria which are assembled to form the phycobilisome. Here, we showed that a small heat shock protein, HspA, interacts directly with phycocyanins from the cyanobacterium Synechococcus sp. strain PCC 7942 in vitro and suppresses inactivation of their light-harvesting functions due to heat denaturation in the presence of hydrogen peroxide.

Light-driven hydrogen production by a hybrid complex of a [NiFe]-hydrogenase and the cyanobacterial photosystem I.

In order to generate renewable and clean fuels, increasing efforts are focused on the exploitation of photosynthetic microorganisms for the production of molecular hydrogen from water and light. In this study we engineered a 'hard-wired' protein complex consisting of a hydrogenase and photosystem I (hydrogenase-PSI complex) as a direct light-to-hydrogen conversion system. The key component was an artificial fusion protein composed of the membrane-bound [NiFe] hydrogenase from the beta-proteobacterium Ralstonia eutropha H16 and the peripheral PSI subunit PsaE of the cyanobacterium Thermosynechococcus elongatus.