Temperature interactions of the molecular chaperone Hsc70 from the eurythermal marine goby Gillichthys mirabilis

Effect of temperature and nucleotide on the binding of BiP chaperone to a protein substrate

BiP (immunoglobulin heavy-chain binding protein) is a Hsp70 monomeric ATPase motor that plays broad and crucial roles in maintaining proteostasis inside the cell. Structurally, BiP is formed by two domains, a nucleotide-binding domain (NBD) with ATPase activity connected by a flexible hydrophobic linker to the substrate-binding domain. While the ATPase and substrate binding activities of BiP are allosterically coupled, the latter is also dependent on nucleotide binding. Recent structural studies have provided new insights into BiP's allostery; however, the influence of temperature on the coupling between substrate and nucleotide binding to BiP remains unexplored. Here, we study BiP's binding to its substrate at the single molecule level using thermo-regulated optical tweezers which allows us to mechanically unfold the client protein and explore the effect of temperature and different nucleotides on BiP binding. Our results confirm that the affinity of BiP for its protein substrate relies on nucleotide binding, by mainly regulating the binding kinetics between BiP and its substrate. Interestingly, our findings also showed that the apparent affinity of BiP for its protein substrate in the presence of nucleotides remains invariable over a wide range of temperatures, suggesting that BiP may interact with its client proteins with similar affinities even when the temperature is not optimal. Thus, BiP could play a role as a "thermal buffer" in proteostasis.

Oxidative stress ecology in brook trout (Salvelinus fontinalis) from a high-mountain lake (Cottian Alps)

High-mountain lakes are pristine ecosystems characterized by extreme environmental conditions. The atmospheric transport of pollutants from lowlands may add further stress to organisms inhabiting these environments. We investigated the environmental stress pressure on brook trout (Salvelinus fontinalis) from a high-mountain lake in the Cottian Alps (Piedmont, northwest Italy). To do this, males and females of brook trout were sampled from Balma Lake in summer (August) and autumn (October) 2017 in order to assess the influence of trace elements accumulation and environmental parameters (physicochemical parameters and nutrient characteristics of water) on oxidative stress biomarkers. Bioaccumulation of Al, As, Cd, Cr, Cu, Fe, Hg, Pb, Ni, Se, and Zn and metallothionein levels were measured in muscle tissue of males and females. Liver, gills, kidney, and spleen tissue samples were analyzed for superoxide dismutase, catalase, total glutathione peroxidase, selenium-dependent glutathione peroxidase, glutathione reductase, and glutathione S-transferase activity. Analysis of environmental parameters showed changes in biomarker levels with seasonal variations. Water temperature was significantly higher in summer than autumn (Wilcoxon test; p = .0078), while pH was significantly higher in autumn than in summer (Wilcoxon test; p = .0078). Sex-related differences in oxidative stress biomarkers in tissues were unremarkable, whereas seasonal variability of oxidative stress biomarkers was observed, with major differences occurred for liver in summer and for gills, kidney, spleen and muscle in autumn. Positive correlations between environmental parameters and biomarkers were noted. Major fluctuations in water temperature, pH, Cu, Pb and Hg produced changes in biomarker levels; however, increased food intake during the ice-free season was probably the main factor that influenced changes in oxidative stress biomarker levels in brook trout in this extreme ecosystem.

Temporal changes in superoxide dismutase, catalase, and heat shock protein 70 gene expression, cortisol and antioxidant enzymes activity of Labeo rohita fingerlings subjected to starvation and refeeding

A short term starvation and refeeding experiment was conducted to study the temporal changes in SOD, CAT and HSP70 gene expression of Labeo rohita fingerlings. The study was carried out for 15 days with initial 7 days of starvation and then refeeding up to 15th day of the experimental trial. The expressions of SOD and CAT genes of liver and gills were significantly up-regulated after 7 days of starvation, down-regulated after 3 days of refeeding, and returned to the basal values after 8 days of refeeding. The HSP70 gene expression was significantly (p < 0.05) increased after starvation, with highest mRNA expression found on 7th day and reduced to the levels of control on refeeding. The activities of antioxidant enzymes, SOD and CAT were also studied to correlate with the results of gene expression. The changes in activities of SOD and CAT were found significantly (p < 0.05) higher in the starved group compared to the fed group. The dynamics of AST and ALT in serum revealed a progressive increase till the 7th day and decreased upon refeeding, cortisol level also has shown significant increase up to 7th day of starvation and sharp decline on refeeding. The concentration of blood glucose level start declining on 3rd day onwards with lowest level found on 7th day of starvation and was quickly restored to the levels of control on refeeding. The present study reveals that starvation elicits oxidative stress response as revealed by enhanced expression and activities of antioxidant enzymes, HSP 70 and serum biochemical alterations. However, these alterations were restored upon refeeding of L. rohita within 7 days.

Synergistic effects of toxic elements on heat shock proteins

Heat shock proteins show remarkable variations in their expression levels under a variety of toxic conditions. A research span expanded over five decades has revealed their molecular characterization, gene regulation, expression patterns, vast similarity in diverse groups, and broad range of functional capabilities. Their functions include protection and tolerance against cytotoxic conditions through their molecular chaperoning activity, maintaining cytoskeleton stability, and assisting in cell signaling. However, their role as biomarkers for monitoring the environmental risk assessment is controversial due to a number of conflicting, validating, and nonvalidating reports. The current knowledge regarding the interpretation of HSPs expression levels has been discussed in the present review. The candidature of heat shock proteins as biomarkers of toxicity is thus far unreliable due to synergistic effects of toxicants and other environmental factors. The adoption of heat shock proteins as "suit of biomarkers in a set of organisms" requires further investigation.

Hsp70 from Cyprinion macrostomus macrostomus and Garra rufa obtuse: stability and stability-dependent activity

Two fish species, Cyprinion macrostomus macrostomus and Garra rufa obtuse, tolerate adverse conditions in the Kangal hot springs and cope with multiple stressors such as food deprivation, extreme temperature, toxins, protein degradation, hypoxia, and microbial damage. These fish have evolved strategies to counteract the stressors including the induction of heat shock proteins (Hsps). Hsps play an essential role in maintaining cellular homeostasis, and one of the key proteins in the mechanism is Hsp70. Hsp70 itself is exposed to the same stressors as all other proteins, and, hence, the stability of Hsp70 was investigated. For this purpose, Hsp70 ATPase activity was determined at different urea concentrations. It was found that the protein maintains considerable ATP hydrolysis activity at higher denaturant conditions. Temperature effects on the substrate peptide binding showed that Hsp70s bind prominently at elevated temperatures. Furthermore, temperature effects on Hsp70 aggregation indicated that the presence of nucleotides decreases the aggregation process. The present work has determined the stability and activity of cmHsp70 and grHsp70 themselves under extreme conditions. The stability of the Hsp70 proteins maintains substrate proteins in the native state, which may aid in the adaptation of the fish species to the hot spring environment.

Different levels of hsp70 and hsc70 mRNA expression in Iberian fish exposed to distinct river conditions

Comprehension of the mechanisms by which ectotherms, such as fish, respond to thermal stress is paramount for understanding the threats that environmental changes may pose to wild populations. Heat shock proteins are molecular chaperones with an important role in several stress conditions such as high temperatures. In the Iberian Peninsula, particularly in Portugal, freshwater fish of the genus Squalius are subject to daily and seasonal temperature variations. To examine the extent to which different thermal regimes influence the expression patterns of hsp70 and hsc70 transcripts we exposed two species of Squalius (S. torgalensis and S. carolitertii) to different temperatures (20, 25, 30 and 35 °C). At 35 °C, there was a significant increase in the expression of hsp70 and hsc70 in the southern species, S. torgalensis, while the northern species, S. carolitertii, showed no increase in the expression of these genes; however, some individuals of the latter species died when exposed to 35 °C. These results suggest that S. torgalensis may cope better with harsher temperatures that are characteristic of this species natural environment; S. carolitertii, on the other hand, may be unable to deal with the extreme temperatures faced by the southern species.

Genomic Cloning of a Heat Shock Cognate 71-1 Gene (HSC71-1) from the Hermaphroditic FishRivulus marmoratus(Cyprinodontiformes, Rivulidae)

The self-fertilizing fish Rivulus marmoratus (R. marmoratus) heat shock cognate 71 (HSC71) gene was cloned and characterized recently (Park et al., 2001). Here, we report the isolation of a homologue of the R. marmoratus HSC71 gene via screening of an R. marmoratus genomic DNA library. A 12,591 bp genomic fragment was sequenced and found to contain a 2844 bp open reading frame that consisted of 8 exons and showed high similarity to the previously reported R. marmoratus HSC71 gene. The two genes differed slightly at exons 5 and 8, and intron 3. On a deduced amino acid sequence level, the two R. marmoratus HSC71 genes were highly similar (89.3% in amino acid residues). In this paper, the author presented a homologous gene (R. marmoratus HSC71-1) similar to R. marmoratus HSC71 gene.

Biochemical adaptations of notothenioid fishes: comparisons between cold temperate South American and New Zealand species and Antarctic species

Fishes of the perciform suborder Notothenioidei afford an excellent opportunity for studying the evolution and functional importance of diverse types of biochemical adaptation to temperature. Antarctic notothenioids have evolved numerous biochemical adaptations to stably cold waters, including antifreeze glycoproteins, which inhibit growth of ice crystals, and enzymatic proteins with cold-adapted specific activities (k(cat) values) and substrate binding abilities (K(m) values), which support metabolism at low temperatures. Antarctic notothenioids also exhibit the loss of certain biochemical traits that are ubiquitous in other fishes, including the heat-shock response (HSR) and, in members of the family Channichthyidae, hemoglobins and myoglobins. Tolerance of warm temperatures is also truncated in stenothermal Antarctic notothenioids. In contrast to Antarctic notothenioids, notothenioid species found in South American and New Zealand waters have biochemistries more reflective of cold-temperate environments. Some of the contemporary non-Antarctic notothenioids likely derive from ancestral species that evolved in the Antarctic and later "escaped" to lower latitude waters when the Antarctic Polar Front temporarily shifted northward during the late Miocene. Studies of cold-temperate notothenioids may enable the timing of critical events in the evolution of Antarctic notothenioids to be determined, notably the chronology of acquisition and amplification of antifreeze glycoprotein genes and the loss of the HSR. Genomic studies may reveal how the gene regulatory networks involved in acclimation to temperature differ between stenotherms like the Antarctic notothenioids and more eurythermal species like cold-temperate notothenioids. Comparative studies of Antarctic and cold-temperate notothenioids thus have high promise for revealing the mechanisms by which temperature-adaptive biochemical traits are acquired - or through which traits that cease to be of advantage under conditions of stable, near-freezing temperatures are lost - during evolution.

Temperature differentially affects adenosine triphosphatase activity in Hsc70 orthologs from Antarctic and New Zealand notothenioid fishes

To test the temperature sensitivity of molecular chaperones in poikilothermic animals, we purified the molecular chaperone Hsc70 from 2 closely related notothenioid fishes--the Antarctic species Trematomus bernacchii and the temperate New Zealand species Notothenia angustata--and characterized the effect of temperature on Hsc70 adenosine triphosphatase (ATPase) activity. Hsc70 ATPase activity was measured using [alpha-32P]-adenosine triphosphate (ATP)-based in vitro assays followed by separation of adenylates by thin-layer chromatography. For both species, a significant increase in Hsc70 ATPase activity was observed across a range of temperatures that was ecologically relevant for each respective species. Hsc70 from T bernacchii hydrolyzed 2-fold more ATP than did N angustata Hsc70 at 0 degrees C, suggesting that the Antarctic molecular chaperone may be adapted to function more efficiently at extreme cold temperatures. In addition, Q10 measurements indicate differential temperature sensitivity of the ATPase activity of Hsc70 from these differentially adapted fish that correlates with the temperature niche inhabited by each species. Hsc70 from T bernacchii was relatively temperature insensitive, as indicated by Q10 values calculated near 1.0 across each temperature range measured. In the case of Hsc70 purified from N angustata, Q10 values indicated thermal sensitivity across the temperature range of 0 degrees C to 10 degrees C, with a Q10 of 2.714. However, Hsc70 from both T bernacchii and N angustata exhibited unusually high thermal stabilities with ATPase activity at temperatures that far exceeded temperatures encountered by these fish in nature. Overall, as evidenced by in vitro ATP hydrolysis, Hsc70 from T bernacchii and N angustata displayed biochemical characteristics that were supportive of molecular chaperone function at ecologically relevant temperatures.

Turning up the heat: The effects of thermal acclimation on the kinetics of hsp70 gene expression in the eurythermal goby, Gillichthys mirabilis

Most organisms respond to temperature fluctuations by altering the expression of an evolutionarily conserved family of proteins known as heat shock proteins (Hsps). Studies have shown Hsp expression and the activation of HSF1, one of the primary regulators of Hsp transcription, are highly malleable, varying with the recent thermal history of the organism; however, the mechanisms that confer plasticity to the regulation of this ubiquitous response are not well-understood. This study furthers our knowledge in this area by characterizing the activation kinetics of HSF1 and the corresponding transcription of hsp70 in the liver of the eurythermal goby, Gillichthys mirabilis, following a month-long acclimation at 13, 21 or 28 degrees C. Our data revealed HSF1 DNA-binding kinetics varied as a function of acclimation temperature and magnitude/duration of exposure, with gobies acclimated at 21 degrees C exhibiting the most robust response. Hsp70 mRNA followed a similar pattern with induction first occurring in the 13 and 21 degrees C fish, and then most robustly in the 28 degrees C group at 36 degrees C. The hsp70 mRNA induction pattern was corroborated by levels of HSF1 DNA-binding activity in each group and may have been lowest in the 28 degrees C group due to the 2-fold greater levels of hsp70 protein prior to thermal exposure. This study illustrates the integral role of HSF1 as a key regulator of Hsp induction and helps explain the plasticity of this response in ectothermic organisms.

Comparison of Hsc70 orthologs from polar and temperate notothenioid fishes: differences in prevention of aggregation and refolding of denatured proteins

Although a great deal is known about the cellular function of molecular chaperones in general, very little is known about the effect of temperature selection on the function of molecular chaperones in nonmodel organisms. One major unanswered question is whether orthologous variants of a molecular chaperone from differential thermally adapted species vary in their thermal responses. To address this issue, we utilized a comparative approach to examine the temperature interactions of a major cytosolic molecular chaperone, Hsc70, from differently thermally adapted notothenioids. Using in vitro assays, we measured the ability of Hsc70 to prevent thermal aggregation of lactate dehydrogenase (LDH). We further compared the capacity of Hsc70 to refold chemically denatured LDH over the temperature range of −2 to +45°C. Hsc70 purified from the temperate species exhibited greater ability to prevent the thermal denaturation of LDH at 55°C compared with Hsc70 from the cold-adapted species. Furthermore, Hsc70 from the Antarctic species lost the ability to competently refold chemically denatured LDH at a lower temperature compared with Hsc70 from the temperate species. These data indicate the function of Hsc70 in notothenioid fishes maps onto their thermal history and that temperature selection has acted on these molecular chaperones.

Magnitude and Duration of Thermal Stress Determine Kinetics ofhspGene Regulation in the GobyGillichthys mirabilis

The stress-induced transcription of heat shock genes is controlled by heat shock transcription factor 1 (HSF1), which becomes activated in response to heat and other protein denaturants. In previous research on the eurythermal goby Gillichthys mirabilis, thermal activation of HSF1 was shown to vary as a function of acclimation temperature, suggesting the mechanistic importance of HSF1 activation to the plasticity of heat shock protein (Hsp) induction temperature. We examined the effect of season on the thermal activation of HSF1 in G. mirabilis, as well as the relative kinetics of HSF1 activation and Hsp70 mRNA production at ecologically relevant temperatures. There was no predictable seasonality in the thermal activation of HSF1, perhaps due to the existence of stressors, in addition to heat, acting in the field. Concentrations of Hsp70, a negative regulator of HSF1, as well as those of HSF1, varied with collection date. The rapidity of HSF1 activation and of Hsp70 mRNA synthesis increased with laboratory exposure temperature. Furthermore, Hsp70 mRNA production was more sustained at 35 degrees C than at 30 degrees C. Therefore, both the magnitude and the duration of a heat shock are important in determining the intensity of heat shock gene induction.

The molecular chaperone Hsc70 from a eurythermal marine goby exhibits temperature insensitivity during luciferase refolding assays

The role and function of molecular chaperones has been widely studied in model systems (e.g. yeast, Escherichia coli and cultured mammalian cells), however, comparatively little is known about the function of molecular chaperones in eurythermal ectotherms. To investigate the thermal sensitivity of molecular chaperone function in non-model ectotherms, we examined the in vitro activity of Hsc70, a constitutively expressed member of the 70-kDa heat-shock protein gene family, purified from white muscle of the eurythermal marine goby Gillichthys mirabilis. The activity of G. mirabilis Hsc70 was assessed with an in vitro refolding assay where the percent refolding of thermally denatured luciferase was monitored using a luminometer. Assays were conducted from 10-40 degrees C, a range of temperatures that is ecologically relevant for this estuarine species. The results showed that isolated Hsc70 displayed chaperone characteristics in vitro, and was relatively thermally insensitive across the range of experimental temperatures. In addition, the thermal stability of the luciferase refolding capacity of Hsc70 was relatively stable, with refolding activity occurring as high as 50 degrees C. Overall, Hsc70 from G. mirabilis displayed thermal properties in vitro that suggest that the molecular chaperone is capable of binding and chaperoning proteins at temperatures that the goby encounters in nature.

Constitutive heat shock protein 70 (HSC70) expression in rainbow trout hepatocytes: effect of heat shock and heavy metal exposure

The 70-kDa family of heat shock proteins plays an important role as molecular chaperones in unstressed and stressed cells. The constitutive member of the 70 family (hsc70) is crucial for the chaperoning function of unstressed cells, whereas the inducible form (hsp70) is important for allowing cells to cope with acute stressor insult, especially those affecting the protein machinery. In fish, the role of hsc70 in the cellular stress response process is less clear primarily because of the lack of a fish-specific antibody for hsc70 detection. In this study, we purified hsc70 to homogeneity from trout liver using a three-step purification protocol with differential centrifugation, ATP-agarose affinity chromatography and electroelution. Polyclonal antibodies to trout hsc70 generated in rabbits cross-reacted strongly with both purified trout hsc70 protein and also purified recombinant bovine hsc70. Two-dimensional electrophoresis followed by Western blotting confirmed that the isoelectric point of rainbow trout hsc70 was more acidic than hsp70. Using this antibody, we detected hsc70 content in the liver, heart, gill and skeletal muscle of unstressed rainbow trout. Primary cultures of trout hepatocytes subjected to a heat shock (+15 degrees C for 1 h) or exposed to either CuSO(4) (200 microM for 24 h), CdCl(2) (10 microM for 24 h) or NaAsO(2) (50 microM for 1 h) resulted in higher hsp70 accumulation over a 24-h period. However, hsc70 content showed no change with either heat shock or heavy metal exposure suggesting that hsc70 is not modulated by sublethal acute stressors in trout hepatocytes. Taken together, we have for the first time generated polyclonal antibodies specific to rainbow trout hsc70 and this antibody will allow for the characterization of the role of hsc70 in the cellular stress response process in fish.