Crystal structure of the hexamer of human heat shock factor binding protein 1

Structural and functional characterization of Hdh-HSBP1 and its involvement in heat stress and early development in Pacific abalone, Haliotis discus hannai

Heat shock factor binding protein 1 (HSBP1) is known to regulate the activity of heat shock factor 1 (HSF1) and the early development of organisms. To understand the involvement of HSBP1 in the heat shock response and embryonic and larval development of Pacific abalone (Haliotis discus hannai), the Hdh-HSBP1 gene was sequenced from the digestive gland (DG) tissue. The full-length sequence of Hdh-HSBP1 encompassed 738 nucleotides, encoding an 8.42 kDa protein consisting of 75 deduced amino acids. The protein contains an HSBP1 domain and a coiled-coil domain, which are conserved features in the HSBP1 protein family. Protein-protein molecular docking revealed that the coiled-coil region of Hdh-HSBP1 binds to the coiled-coil region of Hdh-HSF1. Tissue expression analysis demonstrated that the highest Hdh-HSBP1 expression occurred in the DG, whereas seasonal expression analysis revealed that this gene was most highly expressed in summer. In heat-stressed abalone, the highest expression of Hdh-HSBP1 occurred at 30 °C. Moreover, time-series analysis revealed that the expression of this gene began to increase significantly at 6 h post-heat stress, with higher expression observed at 12 h and 24 h post-heat stress. Furthermore, Hdh-HSBP1 mRNA expression showed a link to ROS production. Additionally, the expression of Hdh-HSBP1 showed significantly higher expression in the early stages of embryonic development in Pacific abalone. These results suggest that Hdh-HSBP1 plays a crucial role in the stress physiology of Pacific abalone by interacting with Hdh-HSF1, as well as its embryonic development.

An 85-amino-acid polypeptide from Myrmeleon bore larvae (antlions) homologous to heat shock factor binding protein 1 with antiproliferative activity against MG-63 osteosarcoma cells in vitro

Background

Venomous arthropods have substances in their venom with antiproliferative potential for neoplastic cells.

Objectives

To identify a polypeptide from Myrmeleon bore (antlion) with antiproliferative activity against neoplastic cells, and to elucidate the molecular mechanism of the activity.

Methods

We used gel filtration and ion exchange chromatography to purify a polypeptide with antiproliferative activity against MG-63 human osteosarcoma cells from a proteinaceous extract of antlion. The polypeptide was sequenced and the stability of its antiproliferative activity was tested under a range of conditions in vitro. An 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay was used to determine the antiproliferative activity of the polypeptide against the MG-63 osteosarcoma cells and MC3T3-E1 mouse calvarial osteoblasts, which were used as a non-neoplastic control. We used western blotting to compare the levels of expression of heat shock transcription factor 1 (HSF1), heat shock protein 90 (HSP90), cyclin-dependent kinase 4 (CDK4), and protein kinase B alpha (ATK1) in MG-63 osteosarcoma cells and their mouse homologs in MC3T3-E1 osteoblasts after their treatment with the antlion antiproliferative polypeptide (ALAPP).

Results

The 85-amino-acid ALAPP has a 56% sequence identity with the human heat shock factor binding protein 1 (HSBP1). The antiproliferative activity of the polypeptide is relatively insensitive to temperature, pH, and metal ions. ALAPP has a strong concentration-dependent antiproliferative activity against MG-63 osteosarcoma cells compared with its effect on MC3T3-E1 osteoblasts. ALAPP significantly upregulates the expression of HSF1 in MC3T3-EL osteoblasts, but not in MG-63 osteosarcoma. ALAPP significantly downregulated the expression of HSP90, CDK4, and AKT1 expression in MG-63 osteosarcoma, but not in the osteoblasts.

Conclusions

ALAPP has significant antiproliferative activity against MG-63 osteosarcoma cells, but not nonneoplastic MC3T3-E1 osteoblasts. We speculate that non-neoplastic cells may evade the antiproliferative effect of ALAPP by upregulating HSF1 to maintain their HSP90, CDK4, and AKT1 expression at a relatively constant level.

HSBP1 Is a Novel Interactor of FIP200 and ATG13 That Promotes Autophagy Initiation and Picornavirus Replication

ATG13 and FIP200 are two subunits of the ULK kinase complex, a key regulatory component of the autophagy machinery. We have previously found that the FIP200-ATG13 subcomplex controls picornavirus replication outside its role in the ULK kinase complex and autophagy. Here, we characterized HSBP1, a very small cytoplasmic coiled-coil protein, as a novel interactor of FIP200 and ATG13 that binds these two proteins via FIP200. HSBP1 is a novel pro-picornaviral host factor since its knockdown or knockout, inhibits the replication of various picornaviruses. The anti-picornaviral function of the FIP200-ATG13 subcomplex was abolished when HSBP1 was depleted, inferring that this subcomplex negatively regulates HSBP1’s pro-picornaviral function during infections. HSBP1depletion also reduces the stability of ULK kinase complex subunits, resulting in an impairment in autophagy induction. Altogether, our data show that HSBP1 interaction with FIP200-ATG13-containing complexes is involved in the regulation of different cellular pathways.

Heteromeric HSFA2/HSFA3 complexes drive transcriptional memory after heat stress in Arabidopsis

Adaptive plasticity in stress responses is a key element of plant survival strategies. For instance, moderate heat stress (HS) primes a plant to acquire thermotolerance, which allows subsequent survival of more severe HS conditions. Acquired thermotolerance is actively maintained over several days (HS memory) and involves the sustained induction of memory-related genes. Here we show that FORGETTER3/ HEAT SHOCK TRANSCRIPTION FACTOR A3 (FGT3/HSFA3) is specifically required for physiological HS memory and maintaining high memory-gene expression during the days following a HS exposure. HSFA3 mediates HS memory by direct transcriptional activation of memory-related genes after return to normal growth temperatures. HSFA3 binds HSFA2, and in vivo both proteins form heteromeric complexes with additional HSFs. Our results indicate that only complexes containing both HSFA2 and HSFA3 efficiently promote transcriptional memory by positively influencing histone H3 lysine 4 (H3K4) hyper-methylation. In summary, our work defines the major HSF complex controlling transcriptional memory and elucidates the in vivo dynamics of HSF complexes during somatic stress memory.

Lin28A Regulates Stem-like Properties of Ovarian Cancer Cells by Enriching RAN and HSBP1 mRNA and Up-regulating its Protein Expression

Ovarian cancer (OC) is one of the malignant tumors that seriously threaten women's health, with the highest mortality rate in gynecological malignancies. The prognosis of patients with advanced OC is still poor, and the 5-year survival rate is only 20-30%. Therefore, how to improve the early diagnosis rate and therapeutic effect are urgent for patients with OC. In this research, we found that Lin28A can promote the expression of stem cell marker molecules CD133, CD44, OCT4 and Nanog. We later confirmed that Lin28A can enrich the mRNA of ras-related nuclear protein (RAN) and heat shock factor binding protein 1 (HSBP1) through RIP assay, and that Lin28A can regulate their protein expression. We also identified that RAN and HSBP1 are highly expressed in OC tissues, and that they are significantly positively correlated with the expression of Lin28A and negatively correlated with the survival prognosis of OC patients. After stable knockdown of RAN or HSBP1 in OC cells with high expression of Lin28A, the expression of the stem cell marker molecules such as OCT4, CD44 and Nanog are reduced. And after knocking down of RAN or HSBP1 in Lin28A highly expressed OC cells, the survival and invasion of OC cells and tumor size of OC xenograft in nude mice were markedly inhibited and apoptosis was increased. Our data also showed that knock down of RAN or HSBP1 can inhibit the invasion ability of OC cells by decreasing the expression of N-cadherin, Vimentin and promoting the expression of E-cadherin. Meanwhile, knockdown of RAN or HSBP1 induced cell apoptosis by inhibiting the expression of PARP. Our results indicated that Lin28A could regulate the biological behaviors in OC cells through RAN/HSBP1. These findings suggest that Lin28A/RAN/HSBP1 can be used as a marker for diagnosis and prognosis of OC patients, and RAN/HSBP1 may be a potential new target for gene therapy of OC.

Intrinsically disordered proteins of viruses: Involvement in the mechanism of cell regulation and pathogenesis

Intrinsically disordered proteins (IDPs) possess the property of inherent flexibility and can be distinguished from other proteins in terms of lack of any fixed structure. Such dynamic behavior of IDPs earned the name "Dancing Proteins." The exploration of these dancing proteins in viruses has just started and crucial details such as correlation of rapid evolution, high rate of mutation and accumulation of disordered contents in viral proteome at least understood partially. In order to gain a complete understanding of this correlation, there is a need to decipher the complexity of viral mediated cell hijacking and pathogenesis in the host organism. Further there is necessity to identify the specific patterns within viral and host IDPs such as aggregation; Molecular recognition features (MoRFs) and their association to virulence, host range and rate of evolution of viruses in order to tackle the viral-mediated diseases. The current book chapter summarizes the aforementioned details and suggests the novel opportunities for further research of IDPs senses in viruses.

Identification and Characterization of a Thermotolerant TILLING Allele of Heat Shock Binding Protein 1 in Tomato

The identification of heat stress (HS)-resilient germplasm is important to ensure food security under less favorable environmental conditions. For that, germplasm with an altered activity of factors regulating the HS response is an important genetic tool for crop improvement. Heat shock binding protein (HSBP) is one of the main negative regulators of HS response, acting as a repressor of the activity of HS transcription factors. We identified a TILLING allele of Solanum lycopersicum (tomato) HSBP1. We examined the effects of the mutation on the functionality of the protein in tomato protoplasts, and compared the thermotolerance capacity of lines carrying the wild-type and mutant alleles of HSBP1. The methionine-to-isoleucine mutation in the central heptad repeats of HSBP1 leads to a partial loss of protein function, thereby reducing the inhibitory effect on Hsf activity. Mutant seedlings show enhanced basal thermotolerance, while mature plants exhibit increased resilience in repeated HS treatments, as shown by several physiological parameters. Importantly, plants that are homozygous for the wild-type or mutant HSBP1 alleles showed no significant differences under non-stressed conditions. Altogether, these results indicate that the identified mutant HSBP1 allele can be used as a genetic tool in breeding, aiming to improve the thermotolerance of tomato varieties.

Temperature shift activates bloodstream VSG expression site promoters in Trypanosoma brucei

Trypanosoma brucei relies on two types of variant surface glycoprotein (VSG) expression sites (ESs) for RNA polymerase I (Pol I) transcription of VSG pre-mRNA. Trypanosomes developing into infectious metacyclic cells in the tsetse vector use metacyclic VSG ESs (MESs) and proliferating parasites in the mammalian host deploy bloodstream VSG ESs (BESs). Unlike the monocistronic MESs, BESs are polycistronic and their highly conserved promoters differ considerably from the MES promoters. The significance of the divergent sequences of MES and BES promoters remains to be determined. We used a reporter system to specifically test the effect of temperature on the activity of MES and BES promoters in procyclic trypanosomes and our results demonstrate that transcription from the MES promoter is largely insensitive to changes in temperature. In contrast, the BES promoter drives rapid activation of transcription upon a change of temperature from 28 °C to 37 °C. Additionally, endogenous BESs respond similarly to the elevation of temperature and initiate increased production of BES pre-mRNA and mRNA. Our results indicate that the sequence of the BES promoter is a specificity signal which triggers BES activation in vivo upon entry into the mammalian host.

The trimeric coiled-coil HSBP1 protein promotes WASH complex assembly at centrosomes

The Arp2/3 complex generates branched actin networks that exert pushing forces onto different cellular membranes. WASH complexes activate Arp2/3 complexes at the surface of endosomes and thereby fission transport intermediates containing endocytosed receptors, such as α5β1 integrins. How WASH complexes are assembled in the cell is unknown. Here, we identify the small coiled-coil protein HSBP1 as a factor that specifically promotes the assembly of a ternary complex composed of CCDC53, WASH, and FAM21 by dissociating the CCDC53 homotrimeric precursor. HSBP1 operates at the centrosome, which concentrates the building blocks. HSBP1 depletion in human cancer cell lines and in Dictyostelium amoebae phenocopies WASH depletion, suggesting a critical role of the ternary WASH complex for WASH functions. HSBP1 is required for the development of focal adhesions and of cell polarity. These defects impair the migration and invasion of tumor cells. Overexpression of HSBP1 in breast tumors is associated with increased levels of WASH complexes and with poor prognosis for patients.

Molecular cloning of hsf1 and hsbp1 cDNAs, and the expression of hsf1, hsbp1 and hsp70 under heat stress in the sea cucumber Apostichopus japonicus

The heat shock response (HSR) is known for the elevated synthesis of heat shock proteins (HSPs) under heat stress, which is mediated primarily by heat shock factor 1 (HSF1). Heat shock factor binding protein 1 (HSBP1) and feedback control of heat shock protein 70 (HSP70) are major regulators of the activity of HSF1. We obtained full-length cDNA of genes hsf1 and hsbp1 in the sea cucumber Apostichopus japonicus, which are the second available for echinoderm (after Strongylocentrotus purpuratus), and the first available for holothurian. The full-length cDNA of hsf1 was 2208bp, containing a 1326bp open reading frame encoding 441 amino acids. The full-length cDNA of hsbp1 was 2850bp, containing a 225bp open reading frame encoding 74 amino acids. The similarities of A. japonicus HSF1 with other species are low, and much higher similarity identities of A. japonicus HSBP1 were shared. Phylogenetic trees showed that A. japonicus HSF1 and HSBP1 were clustered with sequences from S. purpuratus, and fell into distinct clades with sequences from mollusca, arthropoda and vertebrata. Analysis by real-time PCR showed hsf1 and hsbp1 mRNA was expressed constitutively in all tissues examined. The expression of hsf1, hsbp1 and hsp70 in the intestine at 26°C was time-dependent. The results of this study might provide new insights into the regulation of heat shock response in this species.

How does transmembrane electrochemical potential drive the rotation of Fo motor in an ATP synthase?

While the field of ATP synthase research has a long history filled with landmark discoveries, recent structural works provide us with important insights into the mechanisms that links the proton movement with the rotation of the Fo motor. Here, we propose a mechanism of unidirectional rotation of the Fo complex, which is in agreement with these new structural insights as well as our more general ΔΨ-driving hypothesis of membrane proteins: A proton path in the rotor-stator interface is formed dynamically in concert with the rotation of the Fo rotor. The trajectory of the proton viewed in the reference system of the rotor (R-path) must lag behind that of the stator (S-path). The proton moves from a higher energy site to a lower site following both trajectories simultaneously. The two trajectories meet each other at the transient proton-binding site, resulting in a relative rotation between the rotor and stator. The kinetic energy of protons gained from ΔΨ is transferred to the c-ring as the protons are captured sequentially by the binding sites along the proton path, thus driving the unidirectional rotation of the c-ring. Our ΔΨ-driving hypothesis on Fo motor is an attempt to unveil the robust mechanism of energy conversion in the highly conserved, ubiquitously expressed rotary ATP synthases.

Identification of heat shock factor binding protein in Plasmodium falciparum

Background

Heat shock factor binding protein (HSBP) was originally discovered in a yeast two-hybrid screen as an interacting partner of heat shock factor (HSF). It appears to be conserved in all eukaryotes studied so far, with yeast being the only exception. Cell biological analysis of HSBP in mammals suggests its role as a negative regulator of heat shock response as it appears to interact with HSF only during the recovery phase following exposure to heat stress. While the identification of HSF in the malaria parasite is still eluding biologists, this study for the first time, reports the presence of a homologue of HSBP in Plasmodium falciparum.

Methods

PfHSBP was cloned and purified as his-tag fusion protein. CD (Circular dichroism) spectroscopy was performed to predict the secondary structure. Immunoblots and immunofluorescence approaches were used to study expression and localization of HSBP in P. falciparum. Cellular fractionation was performed to examine subcellular distribution of PfHSBP. Immunoprecipitation was carried out to identify HSBP interacting partner in P. falciparum.

Results

PfHSBP is a conserved protein with a high helical content and has a propensity to form homo-oligomers. PfHSBP was cloned, expressed and purified. The in vivo protein expression profile shows maximal expression in trophozoites. The protein was found to exist in oligomeric form as trimer and hexamer. PfHSBP is predominantly localized in the parasite cytosol, however, upon heat shock, it translocates to the nucleus. This study also reports the interaction of PfHSBP with PfHSP70-1 in the cytoplasm of the parasite.

Conclusions

This study emphasizes the structural and biochemical conservation of PfHSBP with its mammalian counterpart and highlights its potential role in regulation of heat shock response in the malaria parasite. Analysis of HSBP may be an important step towards identification of the transcription factor regulating the heat shock response in P. falciparum.

An essential role for heat shock transcription factor binding protein 1 (HSBP1) during early embryonic development

Heat shock factor binding protein 1 (HSBP1) is a 76 amino acid polypeptide that contains two arrays of hydrophobic heptad repeats and was originally identified through its interaction with the oligomerization domain of heat shock factor 1 (Hsf1), suppressing Hsf1's transcriptional activity following stress. To examine the function of HSBP1 in vivo, we generated mice with targeted disruption of the hsbp1 gene and examined zebrafish embryos treated with HSBP1-specific morpholino oligonucleotides. Our results show that hsbp1 is critical for preimplantation embryonic development. Embryonic stem (ES) cells deficient in hsbp1 survive and proliferate normally into the neural lineage in vitro; however, lack of hsbp1 in embryoid bodies (EBs) leads to disorganization of the germ layers and a reduction in the endoderm-specific markers (such as α-fetoprotein). We further show that hsbp1-deficient mouse EBs and knockdown of HSBP1 in zebrafish leads to an increase in the expression of the neural crest inducers Snail2, Tfap2α and Foxd3, suggesting a potential role for HSBP1 in the Wnt pathway. The hsbp1-deficient ES cells, EBs and zebrafish embryos with reduced HSBP1 levels exhibit elevated levels of Hsf1 activity and expression of heat shock proteins (Hsps). We conclude that HSBP1 plays an essential role during early mouse and zebrafish embryonic development.

Functional analysis of OsHSBP1 and OsHSBP2 revealed their involvement in the heat shock response in rice (Oryza sativa L.)

The heat shock response (HSR) induces the production of heat shock proteins (HSPs) through the activation of heat shock factors (HSF). HSF binding protein (HSBP) is reported to modulate the function of HSF by binding to their trimer and hence to regulate HSR. This report describes the role of OsHSBP1 and OsHSBP2 in the regulation of the HSR and seed development of rice. Both genes expressed ubiquitously in all tissues under normal growth conditions while their expression levels were significantly increased during recovery after heat shock treatment. Subcellular localization revealed the cytosol-nuclear localization of both OsHSBP1 and OsHSBP2 in onion epidermal cells. The yeast two-hybrid assay depicted the self-binding ability of both genes. Both genes were also important for seed development, as their knock-down lines were associated with significant seed abortion. The thermotolerance assay revealed that OsHSBP1 and OsHSBP2 are negative regulators of HSR and involved in acquired thermotolerance but not in basal thermotolerance since their over-expression transgenic lines pre-heated at sublethal temperature, showed significantly decreased seedling survival after heat shock treatment. Furthermore, antioxidant activity and gene expression of catalase and peroxidase was significantly increased in knock-down transgenic seedlings of OsHSBP1 and OsHSBP2 after heat stress compared with the wild type. The expression of heat specific HSPs was also increased significantly in knockdown line of both genes but in a specific manner, suggesting the involvement of HSBP genes in different pathways. Overall, the present study reveals the role of OsHSBP1 and OsHSBP2 in the regulation of the HSR and seed development of rice.

Characterisation of hookworm heat shock factor binding protein (HSB-1) during heat shock and larval activation

When hookworm infective L3s infect their mammalian host, they undergo a temperature shift from that of the ambient environment to that of their endothermic host. Additionally, L3s living in the environment can be exposed to temperature extremes associated with weather fluctuations. The heat shock response (HSR) is a conserved response to heat shock and other stress that involves the expression of protective heat shock proteins (HSPs). The HSR is controlled by heat shock factor-1 (HSF-1), a conserved transcription factor that binds to a heat shock element in the promoter of HSPs, causing their expression. HSF-1 is negatively regulated in part by a HSF binding protein (HSB-1) that binds to and removes HSF-1 trimers bound to HSP gene promoters, resulting in attenuation of the HSR. Herein we describe an HSB-1 orthologue, Ac-HSB-1, from the hookworm Ancylostoma caninum. The Ac-hsb-1 cDNA encodes a 79 amino acid protein that is 71% identical to the Caenorhabditis elegans HSB-1, and is predicted to share the characteristic coiled-coil structural motif comprised of two interacting alpha helices. Recombinant Ac-HSB-1 immunoprecipitated Ce-HSF-1 expressed in mammalian cells that had been heat shocked for 1h at 42°C, but not from cells incubated at 37°C, indicating that HSB-1 only bound to the active DNA binding form of HSF-1. Expression of Ac-hsb-1 transcripts decreased following 1h of heat shock, but increased when L3s were incubated at 37°C for 1h. Activation of hookworm L3s induces a five-sixfold increase in Ac-hsb-1 expression that peaks at 12h, coincident with L3 feeding, but that subsequently decreases to two-threefold above control at 24h. Recombinant Ac-HSB-1 immunoprecipitates greater amounts of 70 and 40kDa proteins from extracts of activated L3s than from non-activated L3s. We propose that an increase in Ac-hsb-1 levels early in activation allows feeding to resume, but that a subsequent decrease in expression permits a HSR that protects non-developing L3s at host-like temperatures. Further investigations of the HSR will clarify the role of HSB-1 and HSF-1 in hookworm infection.

Transcriptome responses to heat stress in the nucleated red blood cells of the rainbow trout (Oncorhynchus mykiss)

The retention of a nucleus in the mature state of fish red blood cells (RBCs) and the ability to easily collect and manipulate blood in nonterminal experiments make blood an ideal tissue on which to study the cellular stress response in fish. Through the use of the cGRASP 16K salmonid microarray, we investigated differences in RBC global gene transcription in fish held under control conditions (11°C) and exposed to heat stress (1 h at 25°C followed by recovery at 11°C). Repeated blood sampling (via a dorsal aorta cannula) enables us to examine the individual stress response over time. Samples were taken preheat stress (representing individual control) and at 4 and 24 h postheat stress (representing early and late transcriptional regulation). Approximately 3,000 microarray features had signal above threshold when hybridized with RBC RNA-derived targets, and cannulation did not have a detectable effect on RBC mRNA expression at the investigated time points. Genes involved in the stress response, immune response, and apoptosis were among those showing the highest dysregulation during both early and late transcriptional regulation. Additionally, genes related to the differentiation and development of blood cells were transcriptionally upregulated at the 24 h time point. This study provides a broader understanding of the mechanisms underpinning the stress response in fish and the discovery of novel genes that are regulated in a stress specific manner. Moreover, salmonid transcripts that are consistently dysregulated in blood in response to heat stress are potential candidates of nonlethal biomarkers of exposure to this particular stressor.

AtHSBP functions in seed development and the motif is required for subcellular localization and interaction with AtHSFs

In Arabidopsis thaliana, heat shock factor binding protein (AtHSBP) is a negative regulator of the heat shock response (HSR), and defective AtHSBP leads to seed abortion. We found that the wild-type and AtHSBP-knockout plants did not differ in ovule phenotypes at flower position 3, which indicates that the seed abortion occurs after fertilization and during embryogenesis. The conserved residues of the hydrophobic heptad repeat (HR) domains in AtHSBP were mutated and examined for their subcellular localization and interacting ability with heat shock factors (AtHSFs). The HR domains at the C terminus of AtHSBP are important for retaining AtHSBP in the cytoplasm under normal growth conditions and for interacting with AtHSFs, which negatively affects the DNA-binding capacity and transactivation activity of AtHSFs during the HSR.

Structure-based drug discovery and protein targets in the CNS

Structure-based methods are having an increasing role and impact in drug discovery. The crystal structures of an increasing number of therapeutic targets are becoming available. These structures can transform our understanding of how these proteins perform their biological function and often provide insights into the molecular basis of disease. In addition, the structures can help the discovery process. Methods such as virtual screening and experimental fragment screening can provide starting hit compounds for a discovery project. Crystal structures of compounds bound to the protein can direct or guide the medicinal chemistry optimisation to improve drug-like properties - not only providing ideas on how to improve binding affinity or selectivity, but also showing where the compound can be modified in attempting to modulate physico-chemical properties and biological efficacy. The majority of drug discovery projects against globular protein targets now use these methods at some stage. This review provides a summary of the range of structure-based drug discovery methods that are in use and surveys the suitability of the methods for targets currently identified for CNS drugs. Until recently, structure-based discovery was difficult or unknown for these targets. The recent determination of the structures of a number of GPCR proteins, together with the steady increase in structures for other membrane proteins, is opening up the possibility for these structure-based methods to find increased use in drug discovery for CNS diseases and conditions.

Cytosol-localized heat shock factor-binding protein, AtHSBP, functions as a negative regulator of heat shock response by translocation to the nucleus and is required for seed development in Arabidopsis

Heat shock response (HSR) is a universal mechanism in all organisms. It is under tight regulation by heat shock factors (HSFs) and heat shock proteins (HSPs) after heat shock (HS) to prevent stress damage. On the attenuation of HSR, HSP70 and HSF Binding Protein1 (HSBP1) interact with HSF1 and thus dissociate trimeric HSF1 into an inert monomeric form in humans. However, little is known about the effect of HSBP with thermal stress in plants. This report describes our investigation of the role of AtHSBP in Arabidopsis (Arabidopsis thaliana) by genetic and molecular approaches. AtHSBP was heat inducible and ubiquitously expressed in all tissues; AtHSBP was also crucial for seed development, as demonstrated by AtHSBP-knockout lines showing seed abortion. Thermotolerance results showed that AtHSBP participates in acquired thermotolerance but not basal thermotolerance and is a negative regulator of HSR. Subcellular localization revealed that the cytosol-localized AtHSBP translocated to the nucleus in response to HS. Protoplast two-hybrid assay results confirmed that AtHSBP interacts with itself and with the HSFs, AtHSFA1a, AtHSFA1b, and AtHSFA2. AtHSBP also negatively affected AtHSFA1b DNA-binding capacity in vitro. Quantitative polymerase chain reaction and western-blot analysis demonstrated that altered levels of AtHSBP lead to differential HSP expression, mainly during the recovery from HS. These studies provide a new insight into HSBP in plants and reveal that AtHSBP is a negative regulator of HSR and required for seed development.