Structure and properties of avian small heat shock protein with molecular weight 25 kDa

The Chaperone Activity and Substrate Spectrum of Human Small Heat Shock Proteins

Small heat shock proteins (sHsps) are a ubiquitous family of molecular chaperones that suppress the unspecific aggregation of miscellaneous proteins. Multicellular organisms contain a large number of different sHsps, raising questions as to whether they function redundantly or are specialized in terms of substrates and mechanism. To gain insight into this issue, we undertook a comparative analysis of the eight major human sHsps on the aggregation of both model proteins and cytosolic lysates under standardized conditions. We discovered that sHsps, which form large oligomers (HspB1/Hsp27, HspB3, HspB4/αA-crystallin, and HspB5/αB-crystallin) are promiscuous chaperones, whereas the chaperone activity of the other sHsps is more substrate-dependent. However, all human sHsps analyzed except HspB7 suppressed the aggregation of cytosolic proteins of HEK293 cells. We identified ∼1100 heat-sensitive HEK293 proteins, 12% of which could be isolated in complexes with sHsps. Analysis of their biochemical properties revealed that most of the sHsp substrates have a molecular mass from 50 to 100 kDa and a slightly acidic pI (5.4-6.8). The potency of the sHsps to suppress aggregation of model substrates is correlated with their ability to form stable substrate complexes; especially HspB1 and HspB5, but also B3, bind tightly to a variety of proteins, whereas fewer substrates were detected in complex with the other sHsps, although these were also efficient in preventing the aggregation of cytosolic proteins.

Profiling of differential gene expression in the hypothalamus of broiler-type Taiwan country chickens in response to acute heat stress

Acute heat stress severely impacts poultry production. The hypothalamus acts as a crucial center to regulate body temperature, detect temperature changes, and modulate the autonomic nervous system and endocrine loop for heat retention and dissipation. The purpose of this study was to investigate global gene expression in the hypothalamus of broiler-type B strain Taiwan country chickens after acute heat stress. Twelve 30-week-old hens were allocated to four groups. Three heat-stressed groups were subjected to acute heat stress at 38 °C for 2 hours without recovery (H2R0), with 2 hours of recovery (H2R2), and with 6 hours of recovery (H2R6). The control hens were maintained at 25 °C. At the end, hypothalamus samples were collected for gene expression analysis. The results showed that 24, 11, and 25 genes were upregulated and 41, 15, and 42 genes were downregulated in H2R0, H2R2, and H2R6 treatments, respectively. The expressions of gonadotropin-releasing hormone 1 (GNRH1), heat shock 27-kDa protein 1 (HSPB1), neuropeptide Y (NPY), and heat shock protein 25 (HSP25) were upregulated at all recovery times after heat exposure. Conversely, the expression of TPH2 was downregulated at all recovery times. A gene ontology analysis showed that most of the differentially expressed genes were involved in biological processes including cellular processes, metabolic processes, localization, multicellular organismal processes, developmental processes, and biological regulation. A functional annotation analysis showed that the differentially expressed genes were related to the gene networks of responses to stress and reproductive functions. These differentially expressed genes might be essential and unique key factors in the heat stress response of the hypothalamus in chickens.

Heat shock protein 25-enriched plasma transfusion preconditions the heart against doxorubicin-induced dilated cardiomyopathy in mice

Extracellular heat shock proteins (eHsps) in the circulation have recently been found to activate both apoptotic and protective signaling in the heart. However, the role of eHsps in doxorubicin (Dox)-induced heart failure has not yet been studied. The objective of the present study was to determine how Dox affects circulating eHsp25 in blood plasma and how eHsp25 affects Dox-induced dilated cardiomyopathy. Wild-type mice [HSF-1(+/+)] were pretreated with 100 μl of heterozygous heat shock factor-1 [HSF-1(+/-)] mouse plasma (which contained 4-fold higher eHsp25 compared with wild-type mice), HSF-1(+/+) plasma, or saline, before treatment with Dox (6 mg/kg). After 4 weeks of this treatment protocol, HSF-1(+/-) plasma-pretreated mice showed increased eHsp25 in plasma and improved cardiac function (percentage of fractional shortening 37.3 ± 2.1 versus 26.4 ± 4.0) and better life span (31 ± 2 versus 22 ± 3 days) compared with the HSF-1(+/+) plasma or saline-pretreated mice. Preincubation of isolated adult cardiomyocytes with HSF-1(+/-) plasma or recombinant human Hsp27 (rhHsp27) significantly reduced Dox-induced activation of nuclear factor-κB and cytokine release and delayed cardiomyocyte death. Moreover, when cardiomyocytes were incubated with fluorescence-tagged rhHsp27, a saturation in binding was observed, suggesting that eHsp25 can bind to surface receptors. Competitive assays with a Toll-like receptor 2 (TLR2) antibody reduced the rhHSP27 binding, indicating that Hsp25 interacts with TLR2. In conclusion, transfusion of Hsp25-enriched blood plasma protected the heart from Dox-induced cardiotoxicity. Hsp25 antagonized Dox binding to the TLR2 receptor on cardiomyocytes.

Large potentials of small heat shock proteins

Modern classification of the family of human small heat shock proteins (the so-called HSPB) is presented, and the structure and properties of three members of this family are analyzed in detail. Ubiquitously expressed HSPB1 (HSP27) is involved in the control of protein folding and, when mutated, plays a significant role in the development of certain neurodegenerative disorders. HSPB1 directly or indirectly participates in the regulation of apoptosis, protects the cell against oxidative stress, and is involved in the regulation of the cytoskeleton. HSPB6 (HSP20) also possesses chaperone-like activity, is involved in regulation of smooth muscle contraction, has pronounced cardioprotective activity, and seems to participate in insulin-dependent regulation of muscle metabolism. HSPB8 (HSP22) prevents accumulation of aggregated proteins in the cell and participates in the regulation of proteolysis of unfolded proteins. HSPB8 also seems to be directly or indirectly involved in regulation of apoptosis and carcinogenesis, contributes to cardiac cell hypertrophy and survival and, when mutated, might be involved in development of neurodegenerative diseases. All small heat shock proteins play important "housekeeping" roles and regulate many vital processes; therefore, they are considered as attractive therapeutic targets.

Properties of the monomeric form of human 14-3-3ζ protein and its interaction with tau and HspB6

Dimers formed by seven isoforms of the human 14-3-3 protein participate in multiple cellular processes. The dimeric form has been extensively characterized; however, little is known about the structure and properties of the monomeric form of 14-3-3. The monomeric form is involved in the assembly of homo- and heterodimers, which could partially dissociate back into monomers in response to phosphorylation at Ser58. To obtain monomeric forms of human 14-3-3ζ, we produced four protein constructs with different combinations of mutated (M) or wild-type (W) segments E(5), (12)LAE(14), and (82)YREKIE(87). Under a wide range of expression conditions in Escherichia coli, the MMM and WMM mutants were insoluble, whereas WMW and MMW mutants were soluble, highly expressed, and purified to homogeneity. WMW and MMW mutants remained monomeric over a wide range of concentrations while retaining the α-helical structure characteristic of wild-type 14-3-3. However, WMW and MMW mutants were highly susceptible to proteolysis and had much lower thermal stabilities than the wild-type protein. Using WMW and MMW mutants, we show that the monomeric form interacts with the tau protein and with the HspB6 protein, in both cases forming complexes with a 1:1 stoichiometry, in contrast to the 2:1 and/or 2:2 complexes formed by wild-type 14-3-3. Significantly, this interaction requires phosphorylation of tau protein and HspB6. Because of minimal changes in structure, MMW and especially WMW mutant proteins are promising candidates for analyzing the effect of monomerization on the physiologically important properties of 14-3-3ζ.

14-3-3 proteins and regulation of cytoskeleton

The proteins of the 14-3-3 family are universal adapters participating in multiple processes running in the cell. We describe the structure, isoform composition, and distribution of 14-3-3 proteins in different tissues. Different elements of 14-3-3 structure important for dimer formation and recognition of protein targets are analyzed in detail. Special attention is paid to analysis of posttranslational modifications playing important roles in regulation of 14-3-3 function. The data of the literature concerning participation of 14-3-3 in regulation of intercellular contacts and different elements of cytoskeleton formed by microfilaments are analyzed. We also describe participation of 14-3-3 in regulation of small G-proteins and protein kinases important for proper functioning of cytoskeleton. The data on the interaction of 14-3-3 with different components of microtubules are presented, and the probable role of 14-3-3 in developing of certain neurodegenerative diseases is discussed. The data of the literature concerning the role of 14-3-3 in formation and normal functioning of intermediate filaments are also reviewed. It is concluded that due to its adapter properties 14-3-3 plays an important role in cytoskeleton regulation. The cytoskeletal proteins that are abundant in the cell might compete with the other protein targets of 14-3-3 and therefore can indirectly regulate many intracellular processes that are dependent on 14-3-3.

Phosphorylation dependence of hsp27 multimeric size and molecular chaperone function

The molecular chaperone Hsp27 exists as a distribution of large oligomers that are disassembled by phosphorylation at Ser-15, -78, and -82. It is controversial whether the unphosphorylated Hsp27 or the widely used triple Ser-to-Asp phospho-mimic mutant is the more active molecular chaperone in vitro. This question was investigated here by correlating chaperone activity, as measured by the aggregation of reduced insulin or alpha-lactalbumin, with Hsp27 self-association as monitored by analytical ultracentrifugation. Furthermore, because the phospho-mimic is generally assumed to reproduce the phosphorylated molecule, the size and chaperone activity of phosphorylated Hsp27 were compared with that of the phospho-mimic. Hsp27 was triply phosphorylated by MAPKAP-2 kinase, and phosphorylation was tracked by urea-PAGE. An increasing degree of suppression of insulin or alpha-lactalbumin aggregation correlated with a decreasing Hsp27 self-association, which was the least for phosphorylated Hsp27 followed by the mimic followed by the unphosphorylated protein. It was also found that Hsp27 added to pre-aggregated insulin did not reverse aggregation but did inhibit these aggregates from assembling into even larger aggregates. This chaperone activity appears to be independent of Hsp27 phosphorylation. In conclusion, the most active chaperone of insulin and alpha-lactalbumin was the Hsp27 (elongated) dimer, the smallest Hsp27 subunit observed under physiological conditions. Next, the Hsp27 phospho-mimic is only a partial mimic of phosphorylated Hsp27, both in self-association and in chaperone function. Finally, the efficient inhibition of insulin aggregation by Hsp27 dimer led to the proposal of two models for this chaperone activity.

Differences in the chaperone-like activities of the four main small heat shock proteins of Drosophila melanogaster

The Drosophila melanogaster family of small heat shock proteins (sHsps) is composed of 4 main members (Hsp22, Hsp23, Hsp26, and Hsp27) that display distinct intracellular localization and specific developmental patterns of expression in the absence of stress. In an attempt to determine their function, we have examined whether these 4 proteins have chaperone-like activity using various chaperone assays. Heat-induced aggregation of citrate synthase was decreased from 100 to 17 arbitrary units in the presence of Hsp22 and Hsp27 at a 1:1 molar ratio of sHsp to citrate synthase. A 5 M excess of Hsp23 and Hsp26 was required to obtain the same efficiency with either citrate synthase or luciferase as substrate. In an in vitro refolding assay with reticulocyte lysate, more than 50% of luciferase activity was recovered when heat denaturation was performed in the presence of Hsp22, 40% with Hsp27, and 30% with Hsp23 or Hsp26. These differences in luciferase reactivation efficiency seemed related to the ability of sHsps to bind their substrate at 42 degrees C, as revealed by sedimentation analysis of sHsp and luciferase on sucrose gradients. Therefore, the 4 main sHsps of Drosophila share the ability to prevent heat-induced protein aggregation and are able to maintain proteins in a refoldable state, although with different efficiencies. The functional reasons for their distinctive cell-specific pattern of expression could reflect the existence of defined substrates for each sHsp within the different intracellular compartments.

Evolutionary diversity of vertebrate small heat shock proteins

All vertebrates express multiple small heat shock proteins (sHsps), which are important components of the cellular chaperoning machinery and display a spectacular diversity of functions. This ranges from remodeling the cytoskeleton and inhibiting apoptosis to serving as structural proteins in eye lens and sperm tail. Most information is available for the 10 known mammalian sHsps, formally named HspB1-B10. Only three of them (Hsp27/B1, alphaA-crystallin/B4, alphaB-crystallin/B5) have been reported from nonmammalian vertebrates, while an apparent paralog, Hsp30/B11, is found in frogs and teleost fish. To reconstruct the evolutionary diversification of the sHsps in vertebrates, we searched for additional sHsps in genome, protein, and EST databases and sequenced some avian and amphibian sHsps (HspB2, Hsp30/B11). The urochordate Ciona intestinalis was included in the search, as the outgroup of vertebrates. Orthologs of seven mammalian sHsps were now found in other vertebrate classes. Two novel sHsps, named HspB11 and HspB12, were recognized in birds, and four novel sHsps, named HspB12-B15, in teleost fish. Secondary structure predictions of orthologous sHsps from different vertebrate classes indicate conservation of the beta-sandwich structure of the functionally important C-terminal "alpha-crystallin domain," while the N-terminal domains generally have alpha-helical structures, despite their pronounced sequence variation. The constructed chordate sHsp tree is supported by shared introns, indels, and diagnostic sequences. The tree distinguishes putative orthologous and paralogous relationships, which will facilitate the functional and structural comparison of the various vertebrate sHsps. The 15 recognized paralogous vertebrate sHsps reflect the period of extensive gene duplications early in vertebrate evolution. Eleven of these sHsps are grouped in a clade that might be specific for chordates. It is inferred that at least 13 intron insertions have occurred during the evolution of chordate sHsp genes, while a single ancient intron is maintained in some lineages, in line with the general trend of massive intron gain before or during early vertebrate radiation. Interesting is the occurrence of several head-to-head located pairs of chordate sHsp genes.

pH-induced changes of the structure of small heat shock proteins with molecular mass 24/27kDa (HspB1)

The effect of pH on the structure of recombinant chicken Hsp24, human Hsp27 and their 3D mutants mimicking phosphorylation at Ser15, Ser77/78, and Ser81/82 was analyzed. Circular dichroism and fluorescent spectroscopy indicate that changes of pH in the range 6.0-7.5 weakly affected the secondary and tertiary structure of the wild type proteins, but induced noticeable changes in the structure of their 3D mutants. According to size-exclusion chromatography and analytical ultracentrifugation variation of pH-induced pronounced changes in the quaternary structure of small heat shock proteins and acidification resulted in accumulation of large oligomers of Hsp24/27. It is concluded that small changes of pH strongly affect the quaternary structure of small heat shock proteins and by this means can influence their functioning in the cell.

Some properties of human small heat shock protein Hsp22 (H11 or HspB8)

Untagged recombinant human small heat shock protein with apparent molecular mass 22 kDa (Hsp22) was obtained in homogeneous state. Size exclusion chromatography and chemical crosslinking with dimethylsuberimidate indicate that Hsp22 forms stable dimers. Being highly susceptible to oxidation Hsp22 forms disulfide crosslinked dimers and poorly soluble high molecular mass oligomers. According to CD spectroscopy oxidation of Hsp22 results in disturbing of both secondary and tertiary structure. Hsp22 possesses a negligibly low autophosphorylation activity and under the conditions used is unable to phosphorylate casein or histone. Hsp22 effectively prevents heat-induced aggregation of yeast alcohol dehydrogenase and bovine liver rhodanese with chaperone activity comparable to that of recombinant human small heat shock protein with apparent molecular mass 20 kDa (Hsp20).

Some properties of human small heat shock protein Hsp20 (HspB6)

Human heat shock protein of apparent molecular mass 20 kDa (Hsp20) and its mutant, S16D, mimicking phosphorylation by cyclic nucleotide-dependent protein kinases, were cloned and expressed in Escherichia coli. The proteins were obtained in a homogeneous state without utilization of urea or detergents. On size exclusion chromatography at neutral pH, Hsp20 and its S16D mutant were eluted as symmetrical peaks with an apparent molecular mass of 55-60 kDa. Chemical crosslinking resulted in the formation of dimers with an apparent molecular mass of 42 kDa. At pH 6.0, Hsp20 and its S16D mutant dissociated, and were eluted in the form of two peaks with apparent molecular mass values of 45-50 and 28-30 kDa. At pH 7.0-7.5, the chaperone activity of Hsp20 (measured by its ability to prevent the reduction-induced aggregation of insulin or heat-induced aggregation of yeast alcohol dehydrogenase) was similar to or higher than that of commercial alpha-crystallin. Under these conditions, the S16D mutant of Hsp20 possessed lower chaperone activity than the wild-type protein. At pH 6.0, both alpha-crystallin and Hsp20 interacted with denatured alcohol dehydrogenase; however, alpha-crystallin prevented, whereas Hsp20 either did not affect or promoted, the heat-induced aggregation of alcohol dehydrogenase. The mixing of wild-type human Hsp27 and Hsp20 resulted in a slow, temperature-dependent formation of hetero-oligomeric complexes, with apparent molecular mass values of 100 and 300 kDa, which contained approximately equal amounts of Hsp27 and Hsp20 subunits. Phosphorylation of Hsp27 by mitogen activated protein kinase-activated protein kinase 2 was mimicked by replacing Ser15, 78 and 82 with Asp. A 3D mutant of Hsp27 mixed with Hsp20 rapidly formed a hetero-oligomeric complex with an apparent molecular mass of 100 kDa, containing approximately equal quantities of two small heat shock proteins.

Interaction of the small heat shock protein with molecular mass 25 kDa (hsp25) with actin

The interaction of heat shock protein with molecular mass 25 kDa (HSP25) and its point mutants S77D + S81D (2D mutant) and S15D + S77D + S81D (3D mutant) with intact and thermally denatured actin was analyzed by means of fluorescence spectroscopy and ultracentrifugation. Wild type HSP25 did not affect the polymerization of intact actin. The HSP25 3D mutant decreased the initial rate without affecting the maximal extent of intact actin polymerization. G-actin heated at 40-45 degrees C was partially denatured, but retained its ability to polymerize. The wild type HSP25 did not affect polymerization of this partially denatured actin. The 3D mutant of HSP25 increased the initial rate of polymerization of partially denatured actin. Heating at more than 55 degrees C induced complete denaturation of G-actin. Completely denatured G-actin cannot polymerize, but it aggregates at increased ionic strength. HSP25 and especially its 2D and 3D mutants effectively prevent salt-induced aggregation of completely denatured actin. It is concluded that the interaction of HSP25 with actin depends on the state of both actin and HSP25. HSP25 predominantly acts as a chaperone and preferentially interacts with thermally unfolded actin, preventing the formation of insoluble aggregates.