Thermal activation of the bovine Hsc70 molecular chaperone at physiological temperatures: physical evidence of a molecular thermometer

Cold-induced loss of interaction with HSC70 triggers inflammasome activity of familial cold autoinflammatory syndrome-causing mutants of NLRP3

NLRP3 is a cytoplasmic receptor protein, which initiates caspase-1 mediated inflammatory immune response upon detection of invading pathogen or a wide array of internal distress signals. Several gain-of function mutations of NLRP3 cause hereditary disorder of cold-induced hyper-inflammation known as familial cold autoinflammatory syndrome-1 (FCAS1). Although, caspase-1 activation and downstream interleukin-1β/interleukin-18 maturation are common effectors in pathophysiology of this disorder, molecular mechanisms of how exposure to subnormal temperature triggers mutant NLRP3-inflammsome activity is not understood. Here, we show that endogenous NLRP3 is in complex with HSC70 (HSPA8), and this interaction is reduced upon exposure to cold. FCAS-causing NLRP3-L353P and NLRP3-R260W mutants show enhanced interaction with HSC70. Upon exposure to subnormal temperature, NLRP3-L353P and NLRP3-R260W show enhanced inflammasome formation, increased caspase-1 activation and reduced interaction with HSC70. Knockdown of HSC70 results in increased inflammasome formation by L353P and R260W mutants of NLRP3. Our results suggest that interaction with HSC70 suppresses inflammasome formation by FCAS-causing NLRP3 mutants at physiological temperature, and loss of this inhibitory association at subnormal temperature causes aggravated inflammasome formation and caspase-1 activation leading to interleukin-1β maturation. These results provide evidence for HSC70 being a cold-sensor and a temperature-dependent regulator of inflammatory signaling by FCAS-causing NLRP3 mutants.

HSC70 as a sensor of low temperature: role in cold-triggered autoinflammatory disorders

Familial cold autoinflammatory syndrome (FCAS) is a subset of heritable autoinflammatory disorders wherein inflammatory symptoms aggravate upon exposure of the individual to subnormal temperature. In the past two decades, several mutations in various genes such as NLRP3, NLRP12, PLCG2 and NLRC4 have been identified that cause cold-triggered inflammation. However, our understanding of the mechanisms by which cells perceive subnormal temperature, and what keeps the inflammation under check until exposure to low temperature, is very limited. We hypothesise that recognition of FCAS-associated mutants as misfolded polypeptides by temperature-sensitive HSC70 (HSPA8) chaperone determines the FCAS phenotype. At 37 °C, HSC70 would interact with the mutant proteins, keeping them almost inactive, and loss of interaction at low temperature due to a conformational change in HSC70 would lead to their activation. The proposed mechanism of low temperature sensing in the context of FCAS may have wider implications for HSC70 as a cold temperature sensor in various pathological conditions where symptoms get aggravated upon exposure to low temperature.

Gene family expansions in Antarctic winged midge as a strategy for adaptation to cold environments

Parochlus steinenii is the only flying insect native to Antarctica. To elucidate the molecular mechanisms underlying its adaptation to cold environments, we conducted comparative genomic analyses of P. steinenii and closely related lineages. In an analysis of gene family evolution, 68 rapidly evolving gene families, involved in the innate immune system, unfolded protein response, DNA packaging, protein folding, and unsaturated fatty acid biosynthesis were detected. Some gene families were P. steinenii-specific and showed phylogenetic instability. Acyl-CoA delta desaturase and heat shock cognate protein 70 (Hsc70) were representative gene families, showing signatures of positive selection with multiple gene duplication events. Acyl-CoA delta desaturases may play pivotal roles in membrane fluidity, and expanded Hsc70 genes may function as chaperones or thermal sensors in cold environments. These findings suggest that multiple gene family expansions contributed to the adaptation of P. steinenii to cold environments.

The molecular chaperone Hsp70 from the thermotolerant Diptera species differs from the Drosophila paralog in its thermostability and higher refolding capacity at extreme temperatures

Previously, we demonstrated that species of the Stratiomyidae family exhibit higher tolerance to thermal stress in comparison with that of many representatives of Diptera, including Drosophila species. We hypothesized that species of this group inherited the specific structures of their chaperones from an ancestor of the Stratiomyidae family, and this enabled the descendants to colonize various extreme habitats. To explore this possibility, we cloned and expressed in Escherichia coli copies of the Hsp70 genes from Stratiomys singularior, a typical eurythermal species, and Drosophila melanogaster, for comparison. To investigate the thermal sensitivity of the chaperone function of the inducible 70-kDa heat shock proteins from these species, we used an in vitro refolding luciferase assay. We demonstrated that under conditions of elevated temperature, S. singularior Hsp70 exhibited higher reactivation activity in comparison with D. melanogaster Hsp70 and even human Hsp70. Similarly, S. singularior Hsp70 was significantly more thermostable and showed in vitro refolding activity after preheatment at higher temperatures than D. melanogaster paralog. Thermally induced unfolding experiments using differential scanning calorimetry indicated that Hsp70 from both Diptera species is formed by two domains with different thermal stabilities and that the ATP-binding domain of S. singularior is stable at temperatures 4 degrees higher than that of the D. melanogaster paralog. To the best of our knowledge, this study represents the first report that provides direct experimental data indicating that the evolutionary history of a species may result in adaptive changes in the structures of chaperones to enable them to elicit protective functions at extreme environments.

HSC70 regulates cold-induced caspase-1 hyperactivation by an autoinflammation-causing mutant of cytoplasmic immune receptor NLRC4

NLRC4 [nucleotide-binding domain and leucine-rich repeat (NLR) family, caspase recruitment domain (CARD) containing 4] is an innate immune receptor, which, upon detection of certain pathogens or internal distress signals, initiates caspase-1-mediated interleukin-1β maturation and an inflammatory response. A gain-of-function mutation, H443P in NLRC4, causes familial cold autoinflammatory syndrome (FCAS) characterized by cold-induced hyperactivation of caspase-1, enhanced interleukin-1β maturation, and inflammation. Although the H443P mutant shows constitutive activity, the mechanism involved in hyperactivation of caspase-1 by NLRC4-H443P upon exposure of cells to lower temperature is not known. Here, we show that heat shock cognate protein 70 (HSC70) complexes with NLRC4 and negatively regulates caspase-1 activation by NLRC4-H443P in human cells. Compared with NLRC4, the structurally altered NLRC4-H443P shows enhanced interaction with HSC70. Nucleotide binding- and leucine-rich repeat domains of NLRC4, but not its CARD, can engage in complex formation with HSC70. Knockdown of HSC70 enhances apoptosis-associated speck-like protein containing a CARD (ASC)-speck formation and caspase-1 activation by NLRC4-H443P. Exposure to subnormal temperature results in reduced interaction of NLRC4-H443P with HSC70, and an increase in its ability to form ASC specks and activate caspase-1. Unlike the NLRC4-H443P mutant, another constitutively active mutant (NLRC4-V341A) associated with autoinflammatory diseases, but not FCAS, showed neither enhanced interaction with HSC70 nor an increase in inflammasome formation upon exposure to subnormal temperature. Our results identify HSC70 as a negative regulator of caspase-1 activation by the temperature-sensitive NLRC4-H443P mutant. We also show that low-temperature-induced hyperactivation of caspase-1 by NLRC4-H443P is due to loss of inhibition by HSC70.

The remarkable multivalency of the Hsp70 chaperones

Hsp70 proteins are key to maintaining intracellular protein homeostasis. To carry out this task, they employ a large number of cochaperones and adapter proteins. Here, we review what is known about the interaction between the chaperones and partners, with a strong slant toward structural biology. Hsp70s in general, and Hsc70 (HSPA8) in particular, display an amazing array of interfaces with their protein cofactors. We also review the known interactions between Hsp70s with lipids and with active compounds that may become leads toward Hsp70 modulation for treatment of a variety of diseases.

Bovine neonatal pancytopenia--comparative proteomic characterization of two BVD vaccines and the producer cell surface proteome (MDBK)

Background

Bovine neonatal pancytopenia (BNP) is a disease syndrome in newborn calves of up to four weeks of age, first observed in southern Germany in 2006. By now, cases have been reported in several countries around the globe. Many affected calves die within days due to multiple haemorrhages, thrombocytopenia, leukocytopenia and bone marrow depletion. A certain vaccine directed against Bovine Virus Diarrhoea Virus (BVDV) was recently shown to be associated with BNP pathogenesis. Immunized cows develop alloantibodies that are transferred to newborn calves via colostrum intake. In order to further elucidate BNP pathogenesis, the purpose of this study was to characterize and compare the protein composition of the associated vaccine to another vaccine directed against BVDV not related to BNP and the cell surface proteome of MDBK (Madin-Darby Bovine Kidney) cells, the cell line used for production of the associated vaccine.

Results

By SDS-PAGE and mass spectrometry, we were able to detect several coagulation-related and immune modulatory proteins, as well as cellular and serum derived molecules being shared between the associated vaccine and MDBK cells. Furthermore, the number of proteins identified in the BNP related vaccine was almost as high as the number of surface proteins detected on MDBK cells and exceeded the amount of proteins identified in the non-BNP related vaccine over 3.5 fold. The great amount of shared cellular and serum derived proteins confirm that the BNP associated vaccine contained many molecules originating from MDBK cells and vaccine production.

Conclusions

The respective vaccine was not purified enough to prevent the development of alloantibodies. To narrow down possible candidate proteins, those most likely to represent a trigger for BNP pathogenesis are presented in this study, giving a fundament for further analysis in future research.

High-throughput melting-temperature analysis of a monoclonal antibody by differential scanning fluorimetry in the presence of surfactants

Differential scanning fluorimetry (DSF) is successfully used as a high-throughput screening method for the analysis of the protein melting temperature (T(m)) in the development of therapeutic monoclonal antibody (MAb) formulations. Typically, surfactants are utilized in MAb formulations as a stabilizer, but the commonly applied polarity-sensitive dye SYPRO® Orange shows bright fluorescence in the presence of micelles, concealing the signal of protein unfolding. Studying various MAb formulations containing polysorbate 20, polysorbate 80, or poloxamer 188 (PX 188), the molecular rotor probe 4-(dicyanovinyl)julolidine (DCVJ) was investigated. Although limited to higher MAb concentrations, DCVJ enabled the determination of T(m) in many formulations where SYPRO® Orange failed. It is important to note that careful background correction of placebo formulations is essential for the precise determination of T(m) and especially T(m onset). Thermal shifts of T(m1) (lowest observed thermal transition) indicating stabilizing or destabilizing effects of pH or excipient were in good agreement across all tested formulations and correlated well with differential scanning calorimetry measurements. Additionally, the micellization temperature of PX 188 was confirmed, which leads to a nonproteinous transition. With this new method, it is possible to apply DSF during the development of therapeutic proteins in surfactant-containing formulations.

Biophysical and computational fragment-based approaches to targeting protein-protein interactions: applications in structure-guided drug discovery

Drug discovery has classically targeted the active sites of enzymes or ligand-binding sites of receptors and ion channels. In an attempt to improve selectivity of drug candidates, modulation of protein-protein interfaces (PPIs) of multiprotein complexes that mediate conformation or colocation of components of cell-regulatory pathways has become a focus of interest. However, PPIs in multiprotein systems continue to pose significant challenges, as they are generally large, flat and poor in distinguishing features, making the design of small molecule antagonists a difficult task. Nevertheless, encouragement has come from the recognition that a few amino acids - so-called hotspots - may contribute the majority of interaction-free energy. The challenges posed by protein-protein interactions have led to a wellspring of creative approaches, including proteomimetics, stapled α-helical peptides and a plethora of antibody inspired molecular designs. Here, we review a more generic approach: fragment-based drug discovery. Fragments allow novel areas of chemical space to be explored more efficiently, but the initial hits have low affinity. This means that they will not normally disrupt PPIs, unless they are tethered, an approach that has been pioneered by Wells and co-workers. An alternative fragment-based approach is to stabilise the uncomplexed components of the multiprotein system in solution and employ conventional fragment-based screening. Here, we describe the current knowledge of the structures and properties of protein-protein interactions and the small molecules that can modulate them. We then describe the use of sensitive biophysical methods - nuclear magnetic resonance, X-ray crystallography, surface plasmon resonance, differential scanning fluorimetry or isothermal calorimetry - to screen and validate fragment binding. Fragment hits can subsequently be evolved into larger molecules with higher affinity and potency. These may provide new leads for drug candidates that target protein-protein interactions and have therapeutic value.

Structural biology and drug discovery for protein-protein interactions

Although targeting protein-protein interfaces of regulatory multiprotein complexes has become a significant focus in drug discovery, it continues to pose major challenges. Most interfaces would be classed as 'undruggable' by conventional analyses, as they tend to be large, flat and featureless. Over the past decade, encouragement has come from the discovery of hotspots that contribute much of the free energy of interaction, and this has led to the development of tethering methods that target small molecules to these sites, often inducing adaptive changes. Equally important has been the recognition that many protein-protein interactions involve a continuous epitope of one partner and a well-defined groove or series of specific small pockets. These observations have stimulated the development of stapled α-helical peptides and other proteomimetic approaches. They have also led to the realisation that fragments might gain low-affinity 'footholds' on some protein-protein interfaces, and that these fragments might be elaborated to useful modulators of the interactions.

High throughput methods of assessing protein stability and aggregation

The significant increase in the demand for purified protein for crystallization and structural studies has made necessary the development of multi-sample methods for identifying solution conditions that affect protein stability and aggregation. Conditions that stabilize proteins can improve protein purification and crystallization. These methods can be used to identify small molecule compounds or inhibitors that interact with the purified proteins, and might serve as starting points for drug discovery. In this article three methods for measuring protein stability and aggregation are described and discussed: differential scanning fluorimetry (DSF), differential static light scattering (DSLS), and isothermal denaturation (ITD).

Translocation of constitutively expressed heat shock protein Hsc70 to synapse-enriched areas of the cerebral cortex after hyperthermic stress

Hsp70 is a multi-gene family composed of stress-inducible members (Hsp70) and other members that are constitutively expressed (Hsc70). The heat shock proteins Hsp70 and Hsc70 exhibit similar molecular structure and biochemical functions. Constitutively expressed Hsc70 is enriched in the mammalian nervous system compared with non-neural tissues and present at high levels in neuronal cell bodies. After thermal stress, Hsc70 is translocated to synapse-enriched areas of the cerebral cortex where it associates with Hsp40 to form a complex that can refold denaturated proteins. These results suggest that the heat shock response in the nervous system involves not only the synthesis of stress-inducible Hsps but also the translocation of constitutively expressed Hsc70 to synapse-enriched areas where it could participate in neuroprotective mechanisms that preserved synaptic function during times of stress.

Selection on knockdown performance in Drosophila melanogaster impacts thermotolerance and heat-shock response differently in females and males

We studied adaptive thermotolerance in replicate populations of Drosophila melanogaster artificially selected for high and low knockdown temperature (T(KD)), the upper temperature at which flies can no longer remain upright or locomote effectively. Responses to selection have generated High T(KD) populations capable of maintaining locomotor function at approximately 40 degrees C, and Low T(KD) populations with T(KD) of approximately 35 degrees C. We examined inducible knockdown thermotolerance, as well as inducible thermal survivorship, following a pretreatment heat-shock (known to induce heat-shock proteins) for males and females from the T(KD) selected lines. Both selection for knockdown and sex influenced inducible knockdown thermotolerance, whereas inducible thermal survivorship was influenced only by sex, and not by selection. Overall, our findings suggest that the relationships between basal and inducible thermotolerance are contingent upon the methods used to gauge thermotolerance, as well as the sex of the flies. Finally, we compared temporal profiles of the combined expression of two major heat-shock proteins, HSC70 and HSP70, during heat stress among the females and males from the selected T(KD) lines. The temporal profiles of the proteins differed between High and Low T(KD) females, suggesting divergence of the heat-shock response. We discuss a possible mechanism that may lead to the heat-shock protein patterns observed in the selected females.

Cell mechanics and stress: from molecular details to the ‘universal cell reaction’ and hormesis

The 'universal cell reaction' (UCR), a coordinated biphasic response to external (noxious and other) stimuli observed in all living cells, was described by Nasonov and his colleagues in the mid-20th century. This work has received no attention from cell biologists in the West, but the UCR merits serious consideration. Although it is non-specific, it is likely to be underpinned by precise mechanisms and, if these mechanisms were characterized and their relationship to the UCR elucidated, then our understanding of the integration of cellular function could be improved. As a step towards identifying such mechanisms, I review some recent advances in understanding cell mechanics and the stress response and I suggest potentially testable hypotheses. There is a particular need for time-course studies of cellular responses to different stimulus doses or intensities. I also suggest a correspondence with hormesis; re-investigation of the UCR using modern biophysical and molecular-biological techniques might throw light on this much-discussed phenomenon.

Heat stress-induced localization of small heat shock proteins in mouse myoblasts: intranuclear lamin A/C speckles as target for αB-crystallin and Hsp25

We examined the effect of heat stress on localization of two sHsps, alphaB-crystallin and Hsp25, and of Hsc70, a member of a different class of heat shock proteins (Hsps), in both undifferentiated and differentiated mouse C2C12 cells. Under normal conditions, alphaB-crystallin and Hsp25 are found in the cytoplasm; only alphaB-crystallin is also found in the nucleus, distributed in a speckled pattern. Hsc70 is found to be homogeneously distributed throughout the cell. On heat stress, all these proteins translocate almost entirely into the nucleus and upon recovery relocate to the cytoplasm. Dual staining experiments using C2C12 myoblasts show that alphaB-crystallin and Hsp25, but not Hsc70, colocalize with the intranuclear lamin A/C and the splicing factor SC-35, suggesting interactions of sHsps and intranuclear lamin A/C. Interestingly, none of these proteins are found in the myotube nuclei. Upon heat stress, only Hsc70 translocates into the myotube nuclei. This differential entry of alphaB-crystallin and Hsp25 into the nuclei of myoblasts and myotubes upon heat stress may have functional role in the development and/or in the maintenance of muscle cells. Our study therefore suggests that these sHsps may be a part of the intranuclear lamin A/C network or stabilizing this specific network.

Role of the Conserved SRLFDQFFG Region of α-Crystallin, a Small Heat Shock Protein

Small heat shock proteins (sHsps) are necessary for several cellular functions and in stress tolerance. Most sHsps are oligomers; intersubunit interactions leading to changes in oligomeric structure and exposure of specific regions may modulate their functioning. Many sHsps, including alpha A- and alpha B-crystallin, contain a well conserved SRLFDQFFG sequence motif in the N-terminal region. Sequence-based prediction shows that it exhibits helical propensity with amphipathic character, suggesting that it plays a critical role in the structure and function of alpha-crystallins. In order to investigate the role of this motif in the structure and function of sHsps, we have made constructs deleting this sequence from alpha A- and alpha B-crystallin, overexpressed, purified, and studied these engineered proteins. Circular dichroism spectroscopic studies show changes in tertiary and secondary structure on deletion of the sequence. Glycerol density gradient centrifugation and dynamic light scattering studies show that the multimeric size of the mutant proteins is significantly reduced, indicating a role for this motif in higher order organization of the subunits. Both deletion mutants exhibit similar oligomeric size and increased chaperone-like activity. Urea-induced denaturation study shows that the SRLFDQFFG sequence contributes significantly to the structural stability. Fluorescence resonance energy transfer studies show that the rate of exchange of the subunits in the alpha Adel-crystallin oligomer is higher compared with that in the alpha A-crystallin oligomer, suggesting that this region contributes to the oligomer dynamics in addition to the higher order assembly and structural stability. Thus, our study shows that the SRLFDQFFG sequence is one of the critical motifs in structure-function regulation of alpha A- and alpha B-crystallin.

Structural perturbation and enhancement of the chaperone-like activity of alpha-crystallin by arginine hydrochloride

Structural perturbation of alpha-crystallin is shown to enhance its molecular chaperone-like activity in preventing aggregation of target proteins. We demonstrate that arginine, a biologically compatible molecule that is known to bind to the peptide backbone and negatively charged side-chains, increases the chaperone-like activity of calf eye lens alpha-crystallin as well as recombinant human alphaA- and alphaB-crystallins. Arginine-induced increase in the chaperone activity is more pronounced for alphaB-crystallin than for alphaA-crystallin. Other guanidinium compounds such as aminoguanidine hydrochloride and guanidine hydrochloride also show a similar effect, but to different extents. A point mutation, R120G, in alphaB-crystallin that is associated with desmin-related myopathy, results in a significant loss of chaperone-like activity. Arginine restores the activity of mutant protein to a considerable extent. We have investigated the effect of arginine on the structural changes of alpha-crystallin by circular dichroism, fluorescence, and glycerol gradient sedimentation. Far-UV CD spectra show no significant changes in secondary structure, whereas near-UV CD spectra show subtle changes in the presence of arginine. Glycerol gradient sedimentation shows a significant decrease in the size of alpha-crystallin oligomer in the presence of arginine. Increased exposure of hydrophobic surfaces of alpha-crystallin, as monitored by pyrene-solubilization and ANS-fluorescence, is observed in the presence of arginine. These results show that arginine brings about subtle changes in the tertiary structure and significant changes in the quaternary structure of alpha-crystallin and enhances its chaperone-like activity significantly. This study should prove useful in designing strategies to improve chaperone function for therapeutic applications.

Effects of single nucleotide polymorphisms in the 5'-flanking region of heat shock protein 70.2 gene on semen quality in boars

This study aims to elucidate the effects of single nucleotide polymorphisms (SNPs) in the 5'-flanking region of porcine heat shock protein 70.2 gene (HSP70.2) on semen quality in boars. Genomic DNA isolated from 55 boars (41 Duroc, nine Landrace, and five Yorkshire) was subjected to PCR amplification of the 5'-flanking region of HSP70.2. The nucleotide sequences were determined by automated sequencing. Five SNPs (sites 44, 232, 250, 345, and 393) were detected in this region. Semen quality was evaluated in terms of sperm motility, percentage of normal sperm, percentage of sperm with proximal plasma droplet, percentage of abnormal sperm, sperm concentration, semen volume per ejaculate and total sperm number per ejaculate. The effect of the SNPs on semen quality was evaluated based on breed-corrected data within a season. During the cool season, the sperm motility of boars with AA genotype at the 232 site was significantly higher than that of boars with CC genotype (P<0.05). Meanwhile, boars with AC genotype at the 232 site had higher total sperm number per ejaculate than did those with CC genotype. In the hot season, heterozygotes at both the 232 and 250 sites had significantly higher total sperm number of per ejaculate than AA homozygotes (P<0.05). Semen volume of boars with TT and TC genotypes at the 345 site was significantly larger than that of those with CC genotype (P<0.05). Meanwhile, semen quality for boars with TT genotype at the 345 site was significantly higher than that of boars with TC or CC genotype (P<0.05), that is the semen contained higher percentages of normal sperm and lower percentages of abnormal sperm or sperm with proximal plasma droplets. Results herein suggest that the SNPs in the 5'-flanking region of porcine HSP70.2 are associated with semen quality traits in the hot season.

The nuclear matrix is a thermolabile cellular structure

Heat shock sensitizes cells to ionizing radiation, cells heated in S phase have increased chromosomal aberrations, and both Hsp27 and Hsp70 translocate to the nucleus following heat shock, suggesting that the nucleus is a site of thermal damage. We show that the nuclear matrix is the most thermolabile nuclear component. The thermal denaturation profile of the nuclear matrix of Chinese hamster lung V79 cells, determined by differential scanning calorimetry (DSC), has at least 2 transitions at Tm = 48 degrees C and 55 degrees C with an onset temperature of approximately 40 degrees C. The heat absorbed during these transitions is 1.5 cal/g protein, which is in the range of enthalpies for protein denaturation. There is a sharp increase in 1-anilinonapthalene-8-sulfonic acid (ANS) fluorescence with Tm = 48 degrees C, indicating increased exposure of hydrophobic residues at this transition. The Tm = 48 degrees C transition has a similar Tm to those predicted for the critical targets for heat-induced clonogenic killing (Tm = 46 degrees C) and thermal radiosensitization (Tm = 47 degrees C), suggesting that denaturation of nuclear matrix proteins with Tm = 48 degrees C contribute to these forms of nuclear damage. Following heating at 43 degrees C for 2 hours, Hsc70 binds to isolated nuclear matrices and isolated nuclei, probably because of the increased exposure of hydrophobic domains. In addition, approximately 25% of exogenous citrate synthase also binds, indicating a general increase in aggregation of proteins onto the nuclear matrix. We propose that this is the mechanism for increased association of nuclear proteins with the nuclear matrix observed in nuclei Isolated from heat-shocked cells and is a form of indirect thermal damage.

Redox-regulated chaperone function and conformational changes of Escherichia coli Hsp33

We have studied the chaperone activity and conformation of Escherichia coli heat shock protein (Hsp)33, whose activity is known to be switched on by oxidative conditions. While oxidized Hsp33 completely prevents the heat-induced aggregation of zeta-crystallin at 42 degrees C at a ratio of 1:1 (w/w), the reduced form exhibits only a marginal effect on the aggregation. Far UV-circular dichroism (CD) spectra show that reduced Hsp33 contains a significant alpha-helical component. Oxidation results in significant changes in the far UV-CD spectrum. Near UV-CD spectra show changes in tertiary structural packing upon oxidation. Polarity-sensitive fluorescent probes report enhanced hydrophobic surfaces in the oxidized Hsp33. Our studies show that the oxidative activation of the chaperone function of Hsp33 involves observable conformational changes accompanying increased exposure of hydrophobic pockets.

Association of heat shock protein 70 with semen quality in boars

This study attempted to clarify the relationship between the levels of 70kDa heat shock protein (HSP70) and semen quality in boars. Semen samples from 29 (13 Duroc, 9 Landrace, and 7 Yorkshire) boars (mean age=25.2+/-2.2 months) were examined. Three to four ejaculates per boar, collected during cool and hot seasons, were evaluated in terms of the sperm concentration, sperm motility, percentage of normal and abnormal sperm, as well as percentage of sperm with proximal and distal plasma droplets. Significant seasonal and breed differences in semen quality were observed. Experimental results indicate that the semen quality of Landrace boars was better than those of Yorkshire and Duroc boars (P<0.05) and semen quality declined significantly during the hot season (P<0.05). One-dimensional SDS-PAGE analysis of spermatozoa proteins indicated that protein profiles did not significantly differ between seasons and among breeds. Both constitutive and stress-inducible form of HSP70 were detected in boar spermatozoa by Western blot analysis. The level of HSP70, which revealed no difference among breeds within a season, was significantly lower during the hot season in all the three breeds (P<0.05). Although there appeared to be low correlation coefficients between the level of HSP70 and semen quality traits, the semen quality tended to decline significantly in samples with a lower level of HSP70. Results in this study suggest that the levels of HSP70 in boar spermatozoa are significantly lower during the hot season and might be associated with semen quality.

Heat shock protein 70 (Hsp70) stimulates proliferation and cytolytic activity of natural killer cells

We previously demonstrated that lysis of tumor cells that express Hsp70, the highly stress-inducible member of the HSP70 family, on their plasma membrane is mediated by natural killer (NK) cells. Here, we studied the effects of different proteins of the HSP70 family in combination with interleukin 2 (IL-2) on the proliferation and cytotoxic activity of human NK cells in vitro. Proliferation of NK cells was significantly enhanced by human recombinant Hsp70 (rHsp70) and to a lesser extent by rHsp70homC, the recombinant C-terminal peptide-binding domain derived from Hsp70hom, but not by the constitutive Hsc70 or DnaK, the Escherichia coli analogue of human Hsp70. Even rHsp70 protein alone moderately enhances proliferation and cytolytic activity of NK cells, thus indicating that the stimulatory effect is not strictly dependent on IL-2. NK cells stimulated with rHsp70 protein also exhibit an increased secretion of interferon gamma (IFN-gamma). The phenotypic characterization of NK cells with specificity for Hsp70-expressing tumor cells revealed a CD16dim/CD56bright and increased CD57 and CD94 expression. The cytolytic activity of NK cells also was significantly reduced when a CD94-specific antibody or rHsp70 was added directly before the cytotoxicity assay, whereas other antibodies directed against CD57 and major histocompatibility complex class I molecules or Hsp70 proteins, including Hsc70 and DnaK, did not affect the NK-mediated killing. However, long-term incubation of NK cells with rHsp70 protein enhances not only the proliferative but also the cytolytic response against Hsp70-expressing tumor cells. Our results indicate that the C-terminal domain of Hsp70 protein affects not only the proliferative but also the cytolytic activity of a phenotypically distinct NK cell population with specificity for Hsp70-expressing tumor cells. 1999 International Society for Experimental Hematology.

N-Ethylmaleimide-modified Hsp70 inhibits protein folding

Hsp70 molecular chaperones facilitate protein folding and translocation by binding to hydrophobic regions of nascent or unfolded proteins, thereby preventing their aggregation. N-Ethylmaleimide (NEM) inhibits the ATPase and protein translocation-stimulating activities of the yeast Hsp70 Ssa1p by modifying its three cysteine residues, which are located in its ATPase domain. NEM alters the conformation of Ssa1p and disrupts the coupling between its nucleotide- and polypeptide-binding domains. Ssa1p and the yeast DnaJ homolog Ydj1p constitute a protein folding machinery of the yeast cytosol. Using firefly luciferase as a model protein to study chaperone-dependent protein refolding, we have found that NEM also inhibits the protein folding activity of Ssa1p. Interestingly, the NEM-modified protein (NEM-Ssa1p) is a potent inhibitor of protein folding. NEM-Ssa1p can prevent the aggregation of luciferase and stimulate the ATPase activity of Ssa1p suggesting that it acts as an inhibitor by binding to nonnative forms of luciferase and by competing with them for the polypeptide binding site of Ssa1p. NEM-Ssa1p inhibits Ssa1p/Ydj1p-dependent protein refolding at different stages indicating that the chaperones bind and release nonnative forms of luciferase multiple times before folding is completed.

Heat- and cold-shock responses and temperature adaptations in subtropical and temperate species of Drosophila

Accumulation of Hsp70 mRNA was investigated with relation to heat and cold tolerance in adult males of three Drosophila species. The subtropical lowland species (D. watanabei) and the cool-temperate species (D. triauraria) were more tolerant to heat than the subtropical highland species (D. trapezifrons), and the cool-temperate species were much more tolerant to cold than the two subtropical species. Thus, heat and cold tolerance was related to temperature conditions in the habitats. The threshold temperatures for the induction of Hsp70 mRNA at heat and cold were higher in D. watanabei than in D. trapezifrons or D. triauraria, but were not different between the latter two species in spite of the difference in their heat and cold tolerance. In D. trapezifrons, exposures to 0 degrees C for 12h and 6 degrees C for 24h killed about 40% of individuals, but the former treatment induced Hsp70 mRNA while the latter one did not. Thus, the relation between the heat- and cold-shock responses and temperature tolerance was not rigid in the species studied. In D. triauraria, the threshold temperatures for the induction of Hsp70 mRNA at heat and cold were lower when reared at a lower temperature.

A mathematical model of the hsp70 regulation in the cell

A mathematical model of the regulation process of the heat shock protein hsp70 in the cell is presented. The model describes the damaging effect of elevated temperature on proteins; the interaction of free hsp70 with injured proteins and its chaperone role in nascent protein translation; the relation between the amount of free hsp70 and the formation of the activated trimer form of the heat shock factor protein (HSF); the binding of activated HSF with the heat shock elements on the DNA; the transcription of mRNA of hsp70 and the synthesis of hsp70. The reaction of the model to a temporal rise in temperature shows an initial decline and a subsequent sharp rise to an ultimately increased level of free hsp70 in the cell. The response of the model to both a single and two consecutive heat shocks appears to closely resemble experimental data on hsp70 synthesis. This general agreement demonstrates the structure of the model to be sound and suitable as a basis for further modelling the complex tolerance mechanism of the cell.