Three different DnaK proteins are functionally expressed in the cyanobacterium Synechocystis sp. PCC 6803

Triclosan toxicity in a model cyanobacterium (Anabaena flos-aquae): Growth, photosynthesis and transcriptomic response

Exposure to triclosan (TCS) has been reported to reduce photosynthetic pigments, suppress photosynthesis, and inhibit growth in both prokaryotic and eukaryotic algae including Anabaena flos-aquae (a model cyanobacterium). In particular, cyanobacteria are more sensitive to TCS toxicity compared to eukaryotic algae possibly due to the structural similarity to bacteria (target organisms); however, whether TCS exerts its toxicity to cyanobacteria by targeting signaling pathways of fatty acid biosynthesis as in bacteria remains virtually unknown, particularly at environmental exposure levels. With the complete genome sequence of A. flos-aquae presented in this study, the transcriptomic alterations and potential toxic mechanisms in A. flos-aquae under TCS stress were revealed. The growth, pigments and photosynthetic activity of A. flos-aquae were markedly suppressed following a 7-day TCS exposure at 0.5 µg/L but not 0.1 µg/L (both concentrations applied are environmentally relevant). The transcriptomic sequencing analysis showed that signaling pathways, such as biofilm formation - Pseudomonas aeruginosa, two-component system, starch and sucrose metabolism, and photosynthesis were closely related to the TCS-induced growth inhibition in the 0.5 µg/L TCS treatment. Photosynthesis systems and potentially two-component system were identified to be sensitive targets of TCS toxicity in A. flos-aquae. The present study provides novel insights on TCS toxicity at the transcriptomic level in A. flos-aquae.

DnaK and DnaJ proteins from Hsp70/40 family are involved in Rubisco biosynthesis in Synechocystis sp. PCC6803 and sustain the enzyme assembly in a heterologous system

Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) catalyzes the first step of carbon fixation performed by photosynthetic organisms. Form I of this enzyme found in plants and cyanobacteria is composed of eight large (RbcL) and eight small (RbcS) subunits. To form a functional enzyme, Rubisco subunits need to be properly folded, with the assistance of cellular chaperone machinery, and consecutively assembled in a strictly orchestrated manner, with the help of multiple auxiliary factors. In recent years, multiple Rubisco assembly chaperones and their function in enzyme biogenesis have been extensively characterized. Little is known about the potential specialized factors involved in Rubisco subunits folding at the pre-chaperonin stage, yet this knowledge is greatly needed for the fast and efficient testing of new Rubisco variants.Synechococcus sp. PCC 6803 Rubisco shows limited solubility and a lack of assembly in the Escherichia coli expression system. In this study, we aim to identify which additional chaperones are necessary and sufficient in sustaining the heterologous assembly of native Rubisco. Our findings prove that upon the introduction of Synechocystis DnaK2 to the E. coli system, RbcL is produced in soluble form. The addition of specific DnaJ (Sll1384) enhances this effect. We explain these combined effects based on binding constancies, measured for particular partners in vitro, as well as our analysis of the putative tertiary structure of the proteins. Our results have potential implications for Rubisco engineering.

A DnaK(Hsp70) Chaperone System Connects Type IV Pilus Activity to Polysaccharide Secretion in Cyanobacteria

Surface motility powered by type IV pili (T4P) is widespread among bacteria, including the photosynthetic cyanobacteria. This form of movement typically requires the deposition of a motility-associated polysaccharide, and several studies indicate that there is complex coregulation of T4P motor activity and polysaccharide production, although a mechanistic understanding of this coregulation is not fully defined. Here, using a combination of genetic, comparative genomic, transcriptomic, protein-protein interaction, and cytological approaches in the model filamentous cyanobacterium N. punctiforme, we provided evidence that a DnaK-type chaperone system coupled the activity of the T4P motors to the production of the motility-associated hormogonium polysaccharide (HPS). The results from these studies indicated that DnaK1 and DnaJ3 along with GrpE comprised a chaperone system that interacted specifically with active T4P motors and was required to produce HPS. Genomic conservation in cyanobacteria and the conservation of the protein-protein interaction network in the model unicellular cyanobacterium Synechocystis sp. strain PCC 6803 imply that this system is conserved among nearly all motile cyanobacteria and provides a mechanism to coordinate polysaccharide secretion and T4P activity in these organisms.

Host Plant Adaptation Drives Changes in Diaphorina citri Proteome Regulation, Proteoform Expression, and Transmission of 'Candidatus Liberibacter asiaticus', the Citrus Greening Pathogen

The Asian citrus psyllid (Diaphorina citri) is a pest of citrus and the primary insect vector of the bacterial pathogen, 'Candidatus Liberibacter asiaticus' (CLas), which is associated with citrus greening disease. The citrus relative Murraya paniculata (orange jasmine) is a host plant of D. citri but is more resistant to CLas compared with all tested Citrus genotypes. The effect of host switching of D. citri between Citrus medica (citron) and M. paniculata plants on the acquisition and transmission of CLas was investigated. The psyllid CLas titer and the proportion of CLas-infected psyllids decreased in the generations after transfer from CLas-infected citron to healthy M. paniculata plants. Furthermore, after several generations of feeding on M. paniculata, pathogen acquisition (20 to 40% reduction) and transmission rates (15 to 20% reduction) in psyllids transferred to CLas-infected citron were reduced compared with psyllids continually maintained on infected citron. Top-down (difference gel electrophoresis) and bottom-up (shotgun MS/MS) proteomics methods were used to identify changes in D. citri protein expression resulting from host plant switching between Citrus macrophylla and M. paniculata. Changes in expression of insect metabolism, immunity, and cytoskeleton proteins were associated with host plant switching. Both transient and sustained feeding on M. paniculata induced distinct patterns of protein expression in D. citri compared with psyllids reared on C. macrophylla. The results point to complex interactions that affect vector competence and may lead to strategies to control the spread of citrus greening disease.

Mitochondrial HSP70 Chaperone System-The Influence of Post-Translational Modifications and Involvement in Human Diseases

Since their discovery, heat shock proteins (HSPs) have been identified in all domains of life, which demonstrates their importance and conserved functional role in maintaining protein homeostasis. Mitochondria possess several members of the major HSP sub-families that perform essential tasks for keeping the organelle in a fully functional and healthy state. In humans, the mitochondrial HSP70 chaperone system comprises a central molecular chaperone, mtHSP70 or mortalin (HSPA9), which is actively involved in stabilizing and importing nuclear gene products and in refolding mitochondrial precursor proteins, and three co-chaperones (HSP70-escort protein 1-HEP1, tumorous imaginal disc protein 1-TID-1, and Gro-P like protein E-GRPE), which regulate and accelerate its protein folding functions. In this review, we summarize the roles of mitochondrial molecular chaperones with particular focus on the human mtHsp70 and its co-chaperones, whose deregulated expression, mutations, and post-translational modifications are often considered to be the main cause of neurological disorders, genetic diseases, and malignant growth.

Comparison of alternative integration sites in the chromosome and the native plasmids of the cyanobacterium Synechocystis sp. PCC 6803 in respect to expression efficiency and copy number

Background

Synechocystis sp. PCC 6803 provides a well-established reference point to cyanobacterial metabolic engineering as part of basic photosynthesis research, as well as in the development of next-generation biotechnological production systems. This study focused on expanding the current knowledge on genomic integration of expression constructs in Synechocystis, targeting a range of novel sites in the chromosome and in the native plasmids, together with established loci used in literature. The key objective was to obtain quantitative information on site-specific expression in reference to replicon copy numbers, which has been speculated but never compared side by side in this host.

Results

An optimized sYFP2 expression cassette was successfully integrated in two novel sites in Synechocystis chromosome (slr0944; sll0058) and in all four endogenous megaplasmids (pSYSM/slr5037-slr5038; pSYSX/slr6037; pSYSA/slr7023; pSYSG/slr8030) that have not been previously evaluated for the purpose. Fluorescent analysis of the segregated strains revealed that the expression levels between the megaplasmids and chromosomal constructs were very similar, and reinforced the view that highest expression in Synechocystis can be obtained using RSF1010-derived replicative vectors or the native small plasmid pCA2.4 evaluated in comparison. Parallel replicon copy number analysis by RT-qPCR showed that the expression from the alternative loci is largely determined by the gene dosage in Synechocystis, thereby confirming the dependence formerly proposed based on literature.

Conclusions

This study brings together nine different integrative loci in the genome of Synechocystis to demonstrate quantitative differences between target sites in the chromosome, the native plasmids, and a RSF1010-based replicative expression vector. To date, this is the most comprehensive comparison of alternative integrative sites in Synechocystis, and provides the first direct reference between expression efficiency and replicon gene dosage in the context. In the light of existing literature, the findings support the view that the small native plasmids can be notably more difficult to target than the chromosome or the megaplasmids, and that the RSF1010-derived vectors may be surprisingly well maintained under non-selective culture conditions in this cyanobacterial host. Altogether, the work broadens our views on genomic integration and the rational use of different integrative loci versus replicative plasmids, when aiming at expressing heterologous genes in Synechocystis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12934-021-01622-2.

The J- and G/F-domains of the major Synechocystis DnaJ protein Sll0897 are sufficient for cell viability but not for heat resistance

Hsp70 proteins and their Hsp40 co‐chaperones are essential components of cellular chaperone networks in both prokaryotes and eukaryotes. Here, we performed a genetic analysis to define the protein domains required for the key functions of the major Hsp40/DnaJ protein Sll0897 of the cyanobacterium Synechocystis sp. PCC6803. The expression of the N‐terminally located J‐ and G/F‐domains is essential and sufficient for the proteins’ fundamental in vivo functions, whereas the presence of the full‐length protein, containing the C‐terminal substrate‐binding domains, is crucial under stress conditions.

DnaK3 Is Involved in Biogenesis and/or Maintenance of Thylakoid Membrane Protein Complexes in the Cyanobacterium Synechocystis sp. PCC 6803

DnaK3, a highly conserved cyanobacterial chaperone of the Hsp70 family, binds to cyanobacterial thylakoid membranes, and an involvement of DnaK3 in the biogenesis of thylakoid membranes has been suggested. As shown here, light triggers synthesis of DnaK3 in the cyanobacterium Synechocystis sp. PCC 6803, which links DnaK3 to the biogenesis of thylakoid membranes and to photosynthetic processes. In a DnaK3 depleted strain, the photosystem content is reduced and the photosystem II activity is impaired, whereas photosystem I is regular active. An impact of DnaK3 on the activity of other thylakoid membrane complexes involved in electron transfer is indicated. In conclusion, DnaK3 is a versatile chaperone required for biogenesis and/or maintenance of thylakoid membrane-localized protein complexes involved in electron transfer reactions. As mentioned above, Hsp70 proteins are involved in photoprotection and repair of PS II in chloroplasts.

Functional Implications of Multiple IM30 Oligomeric States

The inner membrane-associated protein of 30 kDa (IM30), also known as the vesicle-inducing protein in plastids 1 (Vipp1), is essential for photo-autotrophic growth of cyanobacteria, algae and higher plants. While its exact function still remains largely elusive, it is commonly accepted that IM30 is crucially involved in thylakoid membrane biogenesis, stabilization and/or maintenance. A characteristic feature of IM30 is its intrinsic propensity to form large homo-oligomeric protein complexes. 15 years ago, it has been reported that these supercomplexes have a ring-shaped structure. However, the in vivo significance of these ring structures is not finally resolved yet and the formation of more complex assemblies has been reported. We here present and discuss research on IM30 conducted within the past 25 years with a special emphasis on the question of why we potentially need IM30 supercomplexes in vivo.

An essential regulatory function of the DnaK chaperone dictates the decision between proliferation and maintenance in Caulobacter crescentus

Hsp70 chaperones are well known for their important functions in maintaining protein homeostasis during thermal stress conditions. In many bacteria the Hsp70 homolog DnaK is also required for growth in the absence of stress. The molecular reasons underlying Hsp70 essentiality remain in most cases unclear. Here, we demonstrate that DnaK is essential in the α-proteobacterium Caulobacter crescentus due to its regulatory function in gene expression. Using a suppressor screen we identified mutations that allow growth in the absence of DnaK. All mutations reduced the activity of the heat shock sigma factor σ³², demonstrating that the DnaK-dependent inactivation of σ³² is a growth requirement. While most mutations occurred in the rpoH gene encoding σ³², we also identified mutations affecting σ³² activity or stability in trans, providing important new insight into the regulatory mechanisms controlling σ³² activity. Most notably, we describe a mutation in the ATP dependent protease HslUV that induces rapid degradation of σ³², and a mutation leading to increased levels of the house keeping σ⁷⁰ that outcompete σ³² for binding to the RNA polymerase. We demonstrate that σ³² inhibits growth and that its unrestrained activity leads to an extensive reprogramming of global gene expression, resulting in upregulation of repair and maintenance functions and downregulation of the growth-promoting functions of protein translation, DNA replication and certain metabolic processes. While this re-allocation from proliferative to maintenance functions could provide an advantage during heat stress, it leads to growth defects under favorable conditions. We conclude that Caulobacter has co-opted the DnaK chaperone system as an essential regulator of gene expression under conditions when its folding activity is dispensable.

Molecular chaperones of the Hsp70 family belong to the most conserved cellular machineries throughout the tree of life. These proteins play key roles in maintaining protein homeostasis, especially under heat stress conditions. In diverse bacteria the Hsp70 homolog DnaK is essential for growth even in the absence of stress. However, the molecular mechanisms underlying the essential nature of DnaK have in most cases not been studied. We found in the α-proteobacterium Caulobacter crescentus that the function of DnaK as a folding catalyst is dispensable in the absence of stress. Instead, its sole essential function under such conditions is to inhibit the activity of the heat shock sigma factor σ³². Our findings highlight that some bacteria have co-opted chaperones as essential regulators of gene expression under conditions when their folding activity is not required. Furthermore, our work illustrates that essential genes can perform different essential functions in discrete growth conditions.

Mechanisms of High Temperature Resistance of Synechocystis sp. PCC 6803: An Impact of Histidine Kinase 34

Synechocystis sp. PCC 6803 is a widely used model cyanobacterium for studying responses and acclimation to different abiotic stresses. Changes in transcriptome, proteome, lipidome, and photosynthesis in response to short term heat stress are well studied in this organism, and histidine kinase 34 (Hik34) is shown to play an important role in mediating such response. Corresponding data on long term responses, however, are fragmentary and vary depending on parameters of experiments and methods of data collection, and thus are hard to compare. In order to elucidate how the early stress responses help cells to sustain long-term heat stress, as well as the role of Hik34 in prolonged acclimation, we examined the resistance to long-term heat stress of wild-type and ΔHik34 mutant of Synechocystis. In this work, we were able to precisely control the long term experimental conditions by cultivating Synechocystis in automated photobioreactors, measuring selected physiological parameters within a time range of minutes. In addition, morphological and ultrastructural changes in cells were analyzed and western blotting of individual proteins was used to study the heat stress-affected protein expression. We have shown that the majority of wild type cell population was able to recover after 24 h of cultivation at 44 °C. In contrast, while ΔHik34 mutant cells were resistant to heat stress within its first hours, they could not recover after 24 h long high temperature treatment. We demonstrated that the early induction of HspA expression and maintenance of high amount of other HSPs throughout the heat incubation is critical for successful adaptation to long-term stress. In addition, it appears that histidine kinase Hik34 is an essential component for the long term high temperature resistance.

The proteome and lipidome of Synechocystis sp. PCC 6803 cells grown under light-activated heterotrophic conditions

Cyanobacteria are photoautotrophic prokaryotes with a plant-like photosynthetic machinery. Because of their short generation times, the ease of their genetic manipulation, and the limited size of their genome and proteome, cyanobacteria are popular model organisms for photosynthetic research. Although the principal mechanisms of photosynthesis are well-known, much less is known about the biogenesis of the thylakoid membrane, hosting the components of the photosynthetic, and respiratory electron transport chain in cyanobacteria. Here we present a detailed proteome analysis of the important model and host organism Synechocystis sp. PCC 6803 under light-activated heterotrophic growth conditions. Because of the mechanistic importance and severe changes in thylakoid membrane morphology under light-activated heterotrophic growth conditions, a focus was put on the analysis of the membrane proteome, which was supported by a targeted lipidome analysis. In total, 1528 proteins (24.5% membrane integral) were identified in our analysis. For 641 of these proteins quantitative information was obtained by spectral counting. Prominent changes were observed for proteins associated with oxidative stress response and protein folding. Because of the heterotrophic growth conditions, also proteins involved in carbon metabolism and C/N-balance were severely affected. Although intracellular thylakoid membranes were significantly reduced, only minor changes were observed in their protein composition. The increased proportion of the membrane-stabilizing sulfoqinovosyl diacyl lipids found in the lipidome analysis, as well as the increased content of lipids with more saturated acyl chains, are clear indications for a coordinated synthesis of proteins and lipids, resulting in stabilization of intracellular thylakoid membranes under stress conditions.

ATP-dependent molecular chaperones in plastids--More complex than expected

Plastids are a class of essential plant cell organelles comprising photosynthetic chloroplasts of green tissues, starch-storing amyloplasts of roots and tubers or the colorful pigment-storing chromoplasts of petals and fruits. They express a few genes encoded on their organellar genome, called plastome, but import most of their proteins from the cytosol. The import into plastids, the folding of freshly-translated or imported proteins, the degradation or renaturation of denatured and entangled proteins, and the quality-control of newly folded proteins all require the action of molecular chaperones. Members of all four major families of ATP-dependent molecular chaperones (chaperonin/Cpn60, Hsp70, Hsp90 and Hsp100 families) have been identified in plastids from unicellular algae to higher plants. This review aims not only at giving an overview of the most current insights into the general and conserved functions of these plastid chaperones, but also into their specific plastid functions. Given that chloroplasts harbor an extreme environment that cycles between reduced and oxidized states, that has to deal with reactive oxygen species and is highly reactive to environmental and developmental signals, it can be presumed that plastid chaperones have evolved a plethora of specific functions some of which are just about to be discovered. Here, the most urgent questions that remain unsolved are discussed, and guidance for future research on plastid chaperones is given. This article is part of a Special Issue entitled: Chloroplast Biogenesis.

Localisation and interactions of the Vipp1 protein in cyanobacteria

The Vipp1 protein is essential in cyanobacteria and chloroplasts for the maintenance of photosynthetic function and thylakoid membrane architecture. To investigate its mode of action we generated strains of the cyanobacteria Synechocystis sp. PCC6803 and Synechococcus sp. PCC7942 in which Vipp1 was tagged with green fluorescent protein at the C-terminus and expressed from the native chromosomal locus. There was little perturbation of function. Live-cell fluorescence imaging shows dramatic relocalisation of Vipp1 under high light. Under low light, Vipp1 is predominantly dispersed in the cytoplasm with occasional concentrations at the outer periphery of the thylakoid membranes. High light induces Vipp1 coalescence into localised puncta within minutes, with net relocation of Vipp1 to the vicinity of the cytoplasmic membrane and the thylakoid membranes. Pull-downs and mass spectrometry identify an extensive collection of proteins that are directly or indirectly associated with Vipp1 only after high-light exposure. These include not only photosynthetic and stress-related proteins but also RNA-processing, translation and protein assembly factors. This suggests that the Vipp1 puncta could be involved in protein assembly. One possibility is that Vipp1 is involved in the formation of stress-induced localised protein assembly centres, enabling enhanced protein synthesis and delivery to membranes under stress conditions.

Cyanobacterial heat-shock response: role and regulation of molecular chaperones

Cyanobacteria constitute a morphologically diverse group of oxygenic photoautotrophic microbes which range from unicellular to multicellular, and non-nitrogen-fixing to nitrogen-fixing types. Sustained long-term exposure to changing environmental conditions, during their three billion years of evolution, has presumably led to their adaptation to diverse ecological niches. The ability to maintain protein conformational homeostasis (folding–misfolding–refolding or aggregation–degradation) by molecular chaperones holds the key to the stress adaptability of cyanobacteria. Although cyanobacteria possess several genes encoding DnaK and DnaJ family proteins, these are not the most abundant heat-shock proteins (Hsps), as is the case in other bacteria. Instead, the Hsp60 family of proteins, comprising two phylogenetically conserved proteins, and small Hsps are more abundant during heat stress. The contribution of the Hsp100 (ClpB) family of proteins and of small Hsps in the unicellular cyanobacteria (Synechocystis and Synechococcus) as well as that of Hsp60 proteins in the filamentous cyanobacteria (Anabaena) to thermotolerance has been elucidated. The regulation of chaperone genes by several cis-elements and trans-acting factors has also been well documented. Recent studies have demonstrated novel transcriptional and translational (mRNA secondary structure) regulatory mechanisms in unicellular cyanobacteria. This article provides an insight into the heat-shock response: its organization, and ecophysiological regulation and role of molecular chaperones, in unicellular and filamentous nitrogen-fixing cyanobacterial strains.

Comparative proteomics reveals that a saxitoxin-producing and a nontoxic strain of Anabaena circinalis are two different ecotypes

In Australia, saxitoxin production is restricted to the cyanobacterial species Anabaena circinalis and is strain-dependent. We aimed to characterize a saxitoxin-producing and nontoxic strain of A. circinalis at the proteomic level using iTRAQ. Seven proteins putatively involved in saxitoxin biosynthesis were identified within our iTRAQ experiment for the first time. The proteomic profile of the toxic A. circinalis was significantly different from the nontoxic strain, indicating that each is likely to inhabit a unique ecological niche. Under control growth conditions, the saxitoxin-producing A. circinalis displayed a higher abundance of photosynthetic, carbon fixation and nitrogen metabolic proteins. Differential abundance of these proteins suggests a higher intracellular C:N ratio and a higher concentration of intracellular 2-oxoglutarate in our toxic strain compared with the nontoxic strain. This may be a novel site for posttranslational regulation because saxitoxin biosynthesis putatively requires a 2-oxoglutarate-dependent dioxygenase. The nontoxic A. circinalis was more abundant in proteins, indicating cellular stress. Overall, our study has provided the first insight into fundamental differences between a toxic and nontoxic strain of A. circinalis, indicating that they are distinct ecotypes.

Vipp1: a very important protein in plastids?!

As a key feature in oxygenic photosynthesis, thylakoid membranes play an essential role in the physiology of plants, algae, and cyanobacteria. Despite their importance in the process of oxygenic photosynthesis, their biogenesis has remained a mystery to the present day. A decade ago, vesicle-inducing protein in plastids 1 (Vipp1) was described to be involved in thylakoid membrane formation in chloroplasts and cyanobacteria. Most follow-up studies clearly linked Vipp1 to membranes and Vipp1 interactions as well as the defects observed after Vipp1 depletion in chloroplasts and cyanobacteria indicate that Vipp1 directly binds to membranes, locally stabilizes bilayer structures, and thereby retains membrane integrity. Here current knowledge about the structure and function of Vipp1 is summarized with a special focus on its relationship to the bacterial phage shock protein A (PspA), as both proteins share a common origin and appear to have retained many similarities in structure and function.

Thermostability of two cyanobacterial GrpE thermosensors

GrpE proteins act as co-chaperones for DnaK heat-shock proteins. The dimeric protein unfolds under heat stress conditions, which results in impaired interaction with a DnaK protein. Since interaction of GrpE with DnaK is crucial for the DnaK chaperone activity, GrpE proteins act as a thermosensor in bacteria. Here we have analyzed the thermostability and function of two GrpE homologs of the mesophilic cyanobacterium Synechocystis sp. PCC 6803 and of the thermophilic cyanobacterium Thermosynechococcus elongatus BP1. While in Synechocystis an N-terminal helix pair of the GrpE dimer appears to be the thermosensing domain and mainly mediates GrpE dimerization, the C-terminal four-helix bundle is involved in additional stabilization of the dimeric structure. The four-helix bundle domain has a key role in the thermophilic cyanobacterium, since dimerization of the Thermosynechococcus protein appears to be mediated by the four-helix bundle domain, and melting of this domain is linked to monomerization of the GrpE protein. Thus, in two related cyanobacteria the GrpE thermosensing function might be mediated by different protein domains.

Specific and promiscuous functions of multiple DnaJ proteins in Synechocystis sp. PCC 6803

Cyanobacterial genomes typically encode multiple Hsp70 (DnaK) and Hsp40 (DnaJ) chaperones, and in the genome of the cyanobacterium Synechocystis PCC 6803, three DnaK proteins are encoded together with seven DnaJ proteins. While only two of the DnaJ proteins can complement the growth defect of an Escherichia coli ΔdnaJ strain, only disruption of the dnaJ gene sll0897 resulted in a growth defect at elevated temperatures. Based on the domain structure and the phenotype observed following disruption of the encoding gene, Sll0897 can be classified as a canonical heat-shock protein in Synechocystis. Furthermore, most dnaJ genes could be deleted individually, whereas disruption of the gene encoding the DnaJ Sll1933 failed, which suggests an essential, yet undefined, function for Sll1933. Since after deletion of the remaining dnaJ genes the phenotypes were not altered, the functions of these DnaJs either are not critical or are taken over by the remaining DnaJs. Nevertheless, only the two dnaJ genes sll0909 and sll1384 could be disrupted in combination, suggesting physiological functions for the two encoded proteins which either are not overlapping and/or can be fulfilled by the remaining DnaJs in the double-disruption strain. Taken together, the present analysis indicates specific and promiscuous functions for multiple DnaJ proteins in Synechocystis.

Similarities and singularities of three DnaK proteins from the cyanobacterium Synechocystis sp. PCC 6803

In the genome of completely sequenced mesophilic cyanobacterium Synechocystis sp. PCC 6803 three DnaK proteins are encoded, which share a high degree of sequence identity in their N-terminal ATPase region as well as in the adjacent peptide-binding domain. However, as typical for DnaK proteins, the C-termini of the three Synechocystis proteins are highly diverse. To study the functions of the three Synechocystis DnaK proteins in more detail, we have analyzed the abundance of the individual proteins in Synechocystis cells as well as dnaK expression under various stress conditions. The presented results show that all three Synechocystis DnaK proteins interact with the same GrpE nucleotide exchange factor. A comparative analysis indicates that DnaK2 is the most abundant DnaK protein in Synechocystis cells and only the expression of dnaK2 is highly up-regulated under various stress conditions. Finally, we show that a small amino acid motif, which is typically conserved at the very C-terminus of cyanobacterial DnaK3 proteins, is essential for the DnaK3 in vivo function.

A 70-kDa molecular chaperone, DnaK, from the industrial bacterium Bacillus licheniformis: gene cloning, purification and molecular characterization of the recombinant protein

The heat shock protein 70 (Hsp70/DnaK) gene of Bacillus licheniformis is 1,839 bp in length encoding a polypeptide of 612 amino acid residues. The deduced amino acid sequence of the gene shares high sequence identity with other Hsp70/DnaK proteins. The characteristic domains typical for Hsps/DnaKs are also well conserved in B. licheniformis DnaK (BlDnaK). BlDnaK was overexpressed in Escherichia coli using pQE expression system and the recombinant protein was purified to homogeneity by nickel-chelate chromatography. The optimal temperature for ATPase activity of the purified BlDnaK was 40°C in the presence of 100 mM KCl. The purified BlDnaK had a V(max) of 32.5 nmol Pi/min and a K(M) of 439 μM. In vivo, the dnaK gene allowed an E. coli dnaK756-ts mutant to grow at 44°C, suggesting that BlDnaK should be functional for survival of host cells under environmental changes especially higher temperature. We also described the use of circular dichroism to characterize the conformation change induced by ATP binding. Binding of ATP was not accompanied by a net change in secondary structure, but ATP together with Mg(2+) and K(+) ions had a greater enhancement in the stability of BlDnaK at stress temperatures. Simultaneous addition of DnaJ, GrpE, and NR-peptide (NRLLLTG) synergistically stimulates the ATPase activity of BlDnaK by 11.7-fold.

Heat pretreatment alleviates UV-B toxicity in the cyanobacterium Anabaena doliolum: A proteomic analysis of cross tolerance

This study offers proteomic elucidation of heat pretreatment-induced alleviation of UV-B toxicity in Anabaena doliolum. Heat-pretreated cells exposed to UV-B showed improved activity of PSI, PSII, whole chain, (14)C fixation, ATP and NADPH contents compared to UV-B alone. Proteomic analysis using two-dimensional gel electrophoresis (2-DE), MALDI-TOF MS/MS and reverse transcription polymerase chain reaction (RT-PCR) of UV-B and heat pretreatment followed by UV-B-treated cells exhibited significant and reproducible alterations in nine proteins homologous to phycocyanin-alpha-chain (PC-alpha-chain), phycoerythrocyanin-alpha-chain (PEC-alpha-chain), hypothetical protein alr0882, phycobilisome core component (PBS-CC), iron superoxide dismutase (Fe-SOD), fructose-1,6-bisphosphate aldolase (FBA), nucleoside diphosphate kinase (NDPK), phosphoribulokinase (PRK) and ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCo) large chain. Except the PEC-alpha-chain, hypothetical protein alr0882 and PBS-CC, all other proteins showed upregulation at low doses of UV-B (U2) and significant downregulation at higher doses of UV-B (U5). The disruption of redox status, signaling, pentose phosphate pathway and Calvin cycle appears to be due to the downregulation of Fe-SOD, NDPK, FBA, PRK and RuBisCo thereby leading to the death of Anabaena. In contrast to this, the upregulation of all the above proteins in heat-pretreated cells, harboring different heat shock proteins (HSPs) like 60, 26 and 16.6, followed by UV-B treatment than only the UV-B-treated ones suggests a protective role of HSPs in mitigating UV-B toxicity.

Copper pretreatment augments ultraviolet B toxicity in the cyanobacterium Anabaena doliolum: a proteomic analysis of cell death

This study provides first-hand proteomic characterisation of Cu-pretreatment-induced augmentation of ultraviolet B toxicity in the cyanobacterium Anabaena doliolum Bharadwaja. Of the three treatments (i.e. Cu, UV-B and Cu + UV-B) tested, the UV-B treatment of Cu-pretreated Anabaena produced a greater inhibition of oxygen evolution, ¹⁴C fixation, ATP and NADPH contents than UV-B alone. Proteomic analysis using two-dimensional gel electrophoresis (2DE), MALDI-TOF MS/MS and reverse transcription polymerase chain reaction (RT-PCR) of Cu, UV-B, and Cu + UV-B treated Anabaena exhibited significant and reproducible alterations in 12 proteins. Of these, manganese superoxide dismutase (Mn-SOD), iron superoxide dismutase (Fe-SOD) and peroxiredoxin (PER) are antioxidative enzymes; ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCo), phosphoribulokinase (PRK), flavodoxin (Flv), plastocyanin (PLC), phosphoglycerate kinase (PGK), phycocyanin (PC) and phycoerythrocyanin α-chain (PC α-chain) are linked with photosynthesis and respiration; and DnaK and nucleoside diphosphate kinase (NDPK) are associated with cellular processes and light signalling, respectively. However, when subjected to a high dose of UV-B, Cu-pretreated Anabaena depicted a severe down-regulation of DnaK, NDPK and Flv, probably because of inevitable oxidative stress. Thus, the augmentation of UV-B toxicity by Cu can be attributed to the down-regulation of DnaK, NDPK and Flv.