Orchardgrass ACTIVATOR OF HSP90 ATPASE possesses autonomous chaperone properties and activates Hsp90 transcription to enhance thermotolerance.

High temperature stress is an environmental factor that negatively affects the growth and development of crops. Hsp90 (90 kDa heat shock protein) is a major molecular chaperone in eukaryotic cells, contributing to the maintenance of cell homeostasis through interaction with co-chaperones. Aha1 (activator of Hsp90 ATPase) is well known as a co-chaperone that activates ATPase activity of Hsp90 in mammals. However, biochemical and physiological evidence relating to Aha has not yet been identified in plants. In this study, we investigated the heat-tolerance function of orchardgrass (Dactylis glomerata L.) Aha (DgAha). Recombinant DgAha interacted with cytosolic DgHsp90s and efficiently protected substrates from thermal denaturation. Furthermore, heterologous expression of DgAha in yeast (Saccharomyces cerevisiae) cells and Arabidopsis (Arabidopsis thaliana) plants conferred thermotolerance in vivo. Enhanced expression of DgAha in Arabidopsis stimulates the transcription of Hsp90 under heat stress. Our data demonstrate that plant Aha plays a positive role in heat stress tolerance via chaperone properties and/or activation of Hsp90 to protect substrate proteins in plants from thermal injury.

N-terminal arm of orchardgrass Hsp17.2 (DgHsp17.2) is essential for both in vitro chaperone activity and in vivo thermotolerance in yeast.

Small heat shock proteins are well-known to function as chaperone in the protection of proteins and subcellular structures against stress-induced denaturation in many cell compartments. Irrespective of such general functional assignment, a proof of function in a living organism is missing. Here, we used heat-induced orchardgrass small Hsp17.2 (DgHsp17.2). Its function in in vitro chaperone properties has shown in protecting the model substrate, malate dehydrogenase (MDH) and citrate synthase (CS). Overexpression of DgHsp17.2 triggering strong chaperone activity enhanced in vivo thermotolerance of yeast cells. To identify the functional domain on DgHsp17.2 and correlationship between in vitro chaperone property and in vivo thermotolerance, we generated truncation mutants of DgHsp17.2 and showed essentiality of the N-terminal arm of DgHsp17.2 for the chaperone function. In addition, beyond for acquisition of thermotolerance irrespective of sequences are diverse among the small Hsps. However, any truncation mutants of DgHsp17.2 did not exhibit strong interaction with orchardgrass heat shock protein 70 (DgHsp70) different from mature DgHsp17.2, indicating that full-length DgHsp17.2 is necessary for cooperating with Hsp70 protein. Our study indicates that the N-terminal arm of DgHsp17.2 is an important region for chaperone activity and thermotolerance.

Identification and functional characterization of Siberian wild rye (Elymus sibiricus L.) small heat shock protein 16.9 gene (EsHsp16.9) conferring diverse stress tolerance in prokaryotic cells.

Small heat shock proteins (Hsps) protect against stress-inducible denaturation of substrates. Our objectives were to clone and examine the mRNA expression of the Hsp16.9 gene from Siberian wild rye grown under diverse stress treatments. We characterized EsHsp16.9 from Elymus sibiricus L. EsHsp16.9 has a 456-bp open reading frame that encodes a 151-amino acid protein with a conserved α-crystallin domain. Northern blot analysis showed that EsHsp16.9 transcripts were enhanced by heat, drought, arsenate, methyl viologen, and H2O2 treatment. In addition, recombinant EsHsp16.9 protein acts as a molecular chaperone to prevent the denaturation of malate dehydrogenase. Growth of cells overexpressing EsHsp16.9 was up to 200% more rapid in the presence of NaCl, arsenate, and polyethylene glycol than that of cells harboring an empty vector. These data suggest that EsHsp16.9 acts as a molecular chaperone that enhances stress tolerance in living organisms.

Structural and functional differences of cytosolic 90-kDa heat-shock proteins (Hsp90s) in Arabidopsis thaliana.

The seven members of the 90-kDa heat shock protein (Hsp90) family encode highly conserved molecular chaperones essential for cell survival in Arabidopsis thaliana. Hsp90 are abundant proteins, localized in different compartments with AtHsp90.1-4 in the cytosol and AtHsp90.5-7 in different organelles. Among the AtHsp90, AtHsp90.1, is stress-inducible and shares comparatively low sequence identity with the constitutively expressed AtHsp90.2-4. Even though abundant information is available on mammalian cytosolic Hsp90 proteins, it is unknown whether cytosolic Hsp90 proteins display different structural and functional properties. We have now analyzed two A. thalianas cytosolic Hsp90s, AtHsp90.1 and AtHsp90.3, for functional divergence. AtHsp90.3 showed higher holdase chaperone activity than AtHsp90.1, although both AtHsp90s exhibited effective chaperone activity. Size-exclusion chromatography revealed different oligomeric states distinguishing the two Hsp90 proteins. While AtHsp90.1 exists in several oligomeric states, including monomers, dimers and higher oligomers, AtHsp90.3 exists predominantly in a high oligomeric state. High oligomeric state of AtHsp90.1 showed higher holdase chaperone activity than the respective monomer or dimer states. When high oligomeric forms of AtHsp90.1 and AtHsp90.3 are reduced by DTT, activity was reduced compared to that found in the native high oligomeric state. In addition, ATP-dependent foldase chaperone activity of AtHsp90.3 was higher with strong intrinsic ATPase activity than that of AtHsp90.1. As a conclusion, the two A. thaliana cytosolic Hsp90 proteins display different functional activities depending on structural differences, implying functional divergence although the proteins are localized to the same sub-cellular organelle.

High level of genetic diversity among Steinernema monticolum in Korea revealed by single-enzyme amplified fragment length polymorphism.

Steinernema monticolum was first described from a mountainous forest at sites of Sancheong, Gyeongnam province in Korea. Since S. monticolum is one of the most commonly isolated entomopathogenic nematodes from Korea, it is desirable to investigate the diversity of this species. Single-enzyme amplified fragment length polymorphism (SE-AFLP) analyses were used to differentiate 32 S. monticolum populations. Our results revealed a high level of genetic diversity within S. monticolum at the population level. On the geographic scale, SE-AFLP analysis revealed that there was no correlation between the genetic similarity of populations of this species and their geographical proximity.

Functional characterization of orchardgrass cytosolic Hsp70 (DgHsp70) and the negative regulation by Ca2+/AtCaM2 binding.

When plants are exposed to extreme temperature, stress-inducible proteins are highly induced and involved in subcellular defence mechanisms. Hsp70, one of stress-inducible proteins, functions as an ATP-dependent molecular chaperone in broad organisms to process such as the inhibition of protein denaturation, promotion of protein folding, and renaturation of denatured proteins. In this study, we isolated a heat-inducible orchardgrass Hsp70 (DgHsp70) that is a homolog of cytosolic Hsp70 that possesses a CaM-binding domain. Purified DgHsp70 protein displayed dose-dependent ATPase, holdase, and ATP-dependent foldase activities. To investigate functional roles of DgHsp70 by the association of Arabidopsis calmodulin-2 (AtCaM2), showing heat-sensitive reduction on transcription, we first characterized the binding activity by gel-overlay assay. DgHsp70 binds to AtCaM2 in the presence of Ca(2+) via a conserved CaM-binding domain. Ca(2+)/AtCaM2 binding decreased ATPase activity of DgHsp70, and concomitantly, reduced foldase activity. Based on the protein structure of bovine Hsc70, which is the closest structural homolog of DgHsp70, a CaM-binding domain is located near the ATP-binding site and CaM may span the ATP-binding pocket of Hsp70. Its decreased functional foldase activity may be caused by blocking ATP hydrolysis after Ca(2+)/AtCaM2 binding. It may associate with inhibition of functional activity of DgHsp70 in the absence of stress and/or de novo protein synthesis of DgHsp70 in the presence of thermal stress condition.

Crystallization and preliminary X-ray data analysis of a DJ-1 homologue from Arabidopsis thaliana (AtDJ-1D).

A DJ-1 homologue protein from Arabidopsis thaliana (AtDJ-1D) belongs to the DJ-1/ThiJ/Pfpl superfamily and contains two tandem arrays of DJ-1-like sequences, but no structural information is available to date for this protein. AtDJ-1D was expressed in Escherichia coli, purified and crystallized for structural analysis. A crystal of AtDJ-1D was obtained by the hanging-drop vapour-diffusion method using 0.22 M NaCl, 0.1 M bis-tris pH 6.5, 21% polyethylene glycol 3350. AtDJ-1D crystals belonged to the monoclinic space group P2(1), with unit-cell parameters a = 56.78, b = 75.21, c = 141.68 Å, ß = 96.87°, and contained a trimer in the asymmetric unit. Diffraction data were collected to 2.05 Å resolution. The structure of AtDJ-1D has been determined using the multiple-wavelength anomalous dispersion (MAD) method.

Potential role of the rice OsCCS52A gene in endoreduplication.

In eukaryotes, the cell cycle consists of four distinct phases: G1, S, G2 and M. In certain condition, the cells skip M-phase and undergo endoreduplication. Endoreduplication, occurring during a modified cell cycle, duplicates the entire genome without being followed by M-phase. A cycle of endoreduplication is common in most of the differentiated cells of plant vegetative tissues and it occurs extensively in cereal endosperm cells. Endoreduplication occurs when CDK/Cyclin complex low or inactive caused by ubiquitin-mediated degradation by APC and their activators. In this study, rice cell cycle switch 52 A (OsCCS52A), an APC activator, is functionally characterized using the reverse genetic approach. In rice, OsCCS52A is highly expressed in seedlings, flowers, immature panicles and 15 DAP kernels. Localization studies revealed that OsCCS52A is a nuclear protein. OsCCS52A interacts with OsCdc16 in yeast. In addition, overexpression of OsCCS52A inhibits mitotic cell division and induces endoreduplication and cell elongation in fission yeast. The homozygous mutant exhibits dwarfism and smaller seeds. Further analysis demonstrated that endoreduplication cycles in the endosperm of mutant seeds were disturbed, evidenced by reduced nuclear and cell sizes. Taken together, these results suggest that OsCCS52A is involved in maintaining normal seed size formation by mediating the exit from mitotic cell division to enter the endoreduplication cycles in rice endosperm.

OsCIPK31, a CBL-interacting protein kinase is involved in germination and seedling growth under abiotic stress conditions in rice plants.

Calcineurin B-like protein-interacting protein kinases (CIPKs) are a group of typical Ser/Thr protein kinases that mediate calcium signals. Extensive studies using Arabidopsis plants have demonstrated that many calcium signatures that activate CIPKs originate from abiotic stresses. However, there are few reports on the functional demonstration of CIPKs in other plants, especially in grasses. In this study, we used a loss-of-function mutation to characterize the function of the rice CIPK gene OsCIPK31. Exposure to high concentrations of NaCl or mannitol effected a rapid and transient enhancement of OsCIPK31 expression. These findings were observed only in the light. However, longer exposure to most stresses resulted in downregulation of OsCIPK31 expression in both the presence and absence of light. To determine the physiological roles of OsCIPK31 in rice plants, the sensitivity of oscipk31::Ds, which is a transposon Ds insertion mutant, to abiotic stresses was examined during germination and seedling stages. oscipk31::Ds mutants exhibited hypersensitive phenotypes to ABA, salt, mannitol, and glucose. Compared with wild-type rice plants, mutants exhibited retarded germination and slow seedling growth. In addition, oscipk31::Ds seedlings exhibited enhanced expression of several stress-responsive genes after exposure to these abiotic stresses. However, the expression of ABA metabolic genes and the endogenous levels of ABA were not altered significantly in the oscipk31::Ds mutant. This study demonstrated that rice plants use OsCIPK31 to modulate responses to abiotic stresses during the seed germination and seedling stages and to modulate the expression of stress-responsive genes.

Functional characterization of orchardgrass endoplasmic reticulum-resident Hsp90 (DgHsp90) as a chaperone and an ATPase.

Hsp90 proteins are essential molecular chaperones regulating multiple cellular processes in distinct subcellular organelles. In this study, we report the functional characterization of a cDNA encoding endoplasmic reticulum (ER)-resident Hsp90 from orchardgrass (DgHsp90). DgHsp90 is a 2742bp cDNA with an open reading frame predicted to encode an 808 amino acid protein. DgHsp90 has a well conserved N-terminal ATPase domain and a C-terminal Hsp90 domain and ER-retention motif. Expression of DgHsp90 increased during heat stress at 35 degrees C or H(2)O(2) treatment. DgHsp90 also functions as a chaperone protein by preventing thermal aggregation of malate dehydrogenase (EC 1.1.1.37) and citrate synthase (EC 2.3.3.1). The intrinsic ATPase activity of DgHsp90 was inhibited by geldanamycin, an Hsp90 inhibitor, and the inhibition reduced the chaperone activity of DgHsp90. Yeast cells overexpressing DgHsp90 exhibited enhanced thermotolerance.

Characterization of orchardgrass p23, a flowering plant Hsp90 cohort protein.

p23 is a heat shock protein 90 (Hsp90) co-chaperone and stabilizes the Hsp90 heterocomplex in mammals and yeast. In this study, we isolated a complementary DNA (cDNA) encoding p23 from orchardgrass (Dgp23) and characterized its functional roles under conditions of thermal stress. Dgp23 is a 911 bp cDNA with an open reading frame predicted to encode a 180 amino acid protein. Northern analysis showed that expression of Dgp23 transcripts was heat inducible. Dgp23 has a well-conserved p23 domain and interacted with an orchardgrass Hsp90 homolog in vivo, like mammalian and yeast p23 homologs. Recombinant Dgp23 is a small acidic protein with a molecular mass of approximately 27 kDa and pI 4.3. Dgp23 was also shown to function as a chaperone protein by suppression of malate dehydrogenase thermal aggregation. Differential scanning calorimetry thermograms indicated that Dgp23 is a heat-stable protein, capable of increasing the T (m) of lysozyme. Moreover, overexpression of Dgp23 in a yeast p23 homolog deletion strain, Deltasba1, increased cell viability. These results suggest that Dgp23 plays a role in thermal stress-tolerance and functions as a co-chaperone of Hsp90 and as a chaperone.

Structure of Chlorobium tepidum sepiapterin reductase complex reveals the novel substrate binding mode for stereospecific production of L-threo-tetrahydrobiopterin.

Sepiapterin reductase (SR) is involved in the last step of tetrahydrobiopterin (BH(4)) biosynthesis by reducing the di-keto group of 6-pyruvoyl tetrahydropterin. Chlorobium tepidum SR (cSR) generates a distinct BH(4) product, L-threo-BH(4) (6R-(1'S,2'S)-5,6,7,8-BH(4)), whereas animal enzymes produce L-erythro-BH(4) (6R-(1'R,2'S)-5,6,7,8-BH(4)) although it has high amino acid sequence similarities to the other animal enzymes. To elucidate the structural basis for the different reaction stereospecificities, we have determined the three-dimensional structures of cSR alone and complexed with NADP and sepiapterin at 2.1 and 1.7 A resolution, respectively. The overall folding of the cSR, the binding site for the cofactor NADP(H), and the positions of active site residues were quite similar to the mouse and the human SR. However, significant differences were found in the substrate binding region of the cSR. In comparison to the mouse SR complex, the sepiapterin in the cSR is rotated about 180 degrees around the active site and bound between two aromatic side chains of Trp-196 and Phe-99 so that its pterin ring is shifted to the opposite side, but its side chain position is not changed. The swiveled sepiapterin binding results in the conversion of the side chain configuration, exposing the opposite face for hydride transfer from NADPH. The different sepiapterin binding mode within the conserved catalytic architecture presents a novel strategy of switching the reaction stereospecificities in the same protein fold.

Expression, purification, crystallization and preliminary X-ray analysis of sepiapterin reductase from Chlorobium tepidum.

Sepiapterin reductase from Chlorobium tepidum (CT-SR) produces L-threo-tetrahydrobiopterin, an isomer of tetrahydrobiopterin, in the last step of de novo synthesis initiating from GTP. Native CT-SR and a selenomethionine (SeMet) derivative of CT-SR have been crystallized by the hanging-drop vapour-diffusion method using PEG 400 as precipitant. CT-SR crystals belong to space group R32, with unit-cell parameters a = b = 201.142, c = 210.184 A, and contain four molecules in the asymmetric unit. Diffraction data were collected to 2.1 A resolution using synchrotron radiation. The structure of CT-SR has been determined using MAD phasing. There is one CT-SR tetramer in the asymmetric unit formed by two closely interacting CT-SR dimers. The solvent content is calculated to be about 67.2%.

Paraquat resistance of transgenic tobacco plants over-expressing the Ochrobactrum anthropi pqrA gene.

Transgenic tobacco plants over-expressing the Ochrobactrum anthropi pqrA gene, which encodes a membrane transporter mediating resistance to paraquat, were generated. Transgenic plants displayed higher resistance against paraquat than wild-type plants, as estimated by plant viability, ion leakage and chlorophyll loss, but no resistance against other active oxygen generators, such as H2O2 and menadione. Moreover, lower levels of paraquat accumulated in transgenic plants, compared to wild-type plants, indicating that the PqrA protein detoxifies paraquat either via increased efflux or decreased uptake of the herbicide, but not by removing active oxygen species. The results collectively demonstrate that the bacterial paraquat resistance gene, pqrA, can be functionally expressed in plant cells, and utilized for the development of paraquat-resistant crop plants.

Structural analysis of thermosome from hyperthermophilic archaeon Thermococcus.

The purification and characterization of thermostable chaperonin of the thermosome family from hyperthermophilic archaeon Thermococcus profunds are described. The purified thermosome is a homooligomeric complex and an ATPase with maximal activity at 80 degrees C. The electron micrographs obtained from negatively stained as well as frozen-hydrated specimen showed an eight-fold symmetry of chaperonin. They were about 15 nm height and 16 nm in diameter with a central cavity of 5 nm. In order to understand the ATPase cycling of thermosome, we analyzed the oligomeric structure of thermosome treated with several nucleotides.