HSP25, a small heat shock protein associated with dense bodies and M-lines of body wall muscle in Caenorhabditis elegans

HspB1 Overexpression Improves Lifespan and Stress Resistance in an Invertebrate Model

To explore the role of the small heat shock protein beta 1 (HspB1, also known as Hsp25 in rodents and Hsp27 in humans) in longevity, we created a Caenorhabiditis elegans model with a high level of ubiquitous expression of the naked mole-rat HspB1 protein. The worms showed increased life span under multiple conditions and also increased resistance to heat stress. RNAi experiments suggest that HspB1-induced life extension is dependent on the transcription factors skn-1 (Nrf2) and hsf-1 (Hsf1). RNAseq from HspB1 worms showed an enrichment in several skn-1 target genes, including collagen proteins and lysosomal genes. Expression of HspB1 also improved functional outcomes regulated by SKN-1, specifically oxidative stress resistance and pharyngeal integrity. This work is the first to link a small heat shock protein with collagen function, suggesting a novel role for HspB1 as a hub between canonical heat response signaling and SKN-1 transcription.

Cold-hearted: A case for cold stress in cancer risk

A negative correlation exists between environmental temperature and cancer risk based on both epidemiological and statistical analyses. Previously, cold stress was reported to be an effective cause of tumorigenesis. Several studies have demonstrated that cold temperature serves as a potential risk factor in cancer development. Most recently, a link was demonstrated between the effects of extreme cold climate on cancer incidence, pinpointing its impact on tumour suppressor genes by causing mutation. The underlying mechanism behind cold stress and its association with tumorigenesis is not well understood. Hence, this review intends to shed light on the role of associated factors, genetic and/or non-genetic, which are modulated by cold temperature, and eventually influence tumorigenic potential. While scrutinizing the effect of cold exposure on the body, the expression of certain genes, e.g. uncoupled proteins and heat-shock proteins, were elevated. Biological chemicals such as norepinephrine, thyroxine, and cholesterol were also elevated. Brown adipose tissue, which plays an essential role in thermogenesis, displayed enhanced activity upon cold exposure. Adaptive measures are utilized by the body to tolerate the cold, and in doing so, invites both epigenetic and genetic changes. Unknowingly, these adaptive strategies give rise to a lethal outcome i.e., genesis of cancer. Concisely, this review attempts to draw a link between cold stress, genetic and epigenetic changes, and tumorigenesis and aspires to ascertain the mechanism behind cold temperature-mediated cancer risk.

A Differentiation Transcription Factor Establishes Muscle-Specific Proteostasis in Caenorhabditis elegans

Safeguarding the proteome is central to the health of the cell. In multi-cellular organisms, the composition of the proteome, and by extension, protein-folding requirements, varies between cells. In agreement, chaperone network composition differs between tissues. Here, we ask how chaperone expression is regulated in a cell type-specific manner and whether cellular differentiation affects chaperone expression. Our bioinformatics analyses show that the myogenic transcription factor HLH-1 (MyoD) can bind to the promoters of chaperone genes expressed or required for the folding of muscle proteins. To test this experimentally, we employed HLH-1 myogenic potential to genetically modulate cellular differentiation of Caenorhabditis elegans embryonic cells by ectopically expressing HLH-1 in all cells of the embryo and monitoring chaperone expression. We found that HLH-1-dependent myogenic conversion specifically induced the expression of putative HLH-1-regulated chaperones in differentiating muscle cells. Moreover, disrupting the putative HLH-1-binding sites on ubiquitously expressed daf-21(Hsp90) and muscle-enriched hsp-12.2(sHsp) promoters abolished their myogenic-dependent expression. Disrupting HLH-1 function in muscle cells reduced the expression of putative HLH-1-regulated chaperones and compromised muscle proteostasis during and after embryogenesis. In turn, we found that modulating the expression of muscle chaperones disrupted the folding and assembly of muscle proteins and thus, myogenesis. Moreover, muscle-specific over-expression of the DNAJB6 homolog DNJ-24, a limb-girdle muscular dystrophy-associated chaperone, disrupted the muscle chaperone network and exposed synthetic motility defects. We propose that cellular differentiation could establish a proteostasis network dedicated to the folding and maintenance of the muscle proteome. Such cell-specific proteostasis networks can explain the selective vulnerability that many diseases of protein misfolding exhibit even when the misfolded protein is ubiquitously expressed.

Molecular chaperones protect proteins from misfolding and aggregation. In multi-cellular organisms, the composition and expression levels of chaperones vary between tissues. However, little is known of how such differential expression is regulated. We hypothesized that the cellular differentiation that regulates the cell-type specific expression program may be involved in establishing a cell-type specific chaperone network. To test this possibility, we addressed the myogenic commitment transcription factor HLH-1 (CeMyoD) that converts embryonic cells to muscle cells in Caenorhabditis elegans. We demonstrated that HLH-1 regulates the expression of muscle chaperones during muscle differentiation. Moreover, we showed that HLH-1-dependent expression of chaperones is required for embryonic development and muscle function. We propose that cellular differentiation results in cell-specific differences in the chaperone network that may be detrimental in terms of the susceptibility of neurons and muscle cells to protein misfolding diseases.

Molecular Characterization of Six Small Heat Shock Proteins and Their Responses Under Cadmium Stress in Oxya chinensis (Orthoptera: Acridoidea)

Small heat shock proteins (sHSPs) have been implicated in many physiological processes and play important roles in the response to various stresses. In this study, the full-length sequences of six sHSPs: OcHSP19.1, 19.8, 20.4, 20.7, 21.1, and 23.8 were obtained from the rice grasshopper Oxya chinensis transcriptome database. The deduced amino acid sequences of the six OcsHSPs contain a typical α-crystallin domain, which consists of approximately 100 amino acid residues and five β-strands. The phylogenetic analysis suggested that OcHSP23.8 was orthologous to the sHSPs of other species and that OcHSP19.1, 20.4, 20.7, and 21.1 were species specific, whereas OcHSP19.8 did not cluster closely to Orthoptera but was placed on the basal end of the cluster. Developmental stage-dependent and tissue-specific expression patterns were evaluated using quantitative real-time polymerase chain reaction. The six genes were expressed in all developmental stages and showed clear tissue specificity. The cadmium acute experiment indicates that Cd(2+) can induce the six genes. However, various response patterns were observed among these genes under Cd(2+) stress conditions. OcHSP19.1, 19.8, 20.4, and 20.7 were highly induced by 2.61 mM Cd(2+) at 24 h. OcHSP23.8 was significantly upregulated by 2.61 mM Cd(2+) at 6 h. For OcHSP21.1, the highest expression levels were found after treatment with 0.87 mM Cd(2+) for 24 h, 1.74 mM Cd(2+) for 36 h, and 2.61 mM Cd(2+) for 12 h. These differential characteristics will facilitate future investigations into the physiological functions of sHSPs.

Twitchin kinase interacts with MAPKAP kinase 2 in Caenorhabditis elegans striated muscle

Titin-like giant polypeptides of muscle have protein kinase domains near their C-termini. These kinases are autoinhibited by portions of their own sequences. A putative activator for Caenorhabditis elegans twitchin kinase, MAK-1 (MAPKAP kinase 2), is expressed in nematode striated muscle, partially colocalizes with twitchin in sarcomeres, and binds to and phosphorylates twitchin kinase in vitro.

In Caenorhabditis elegans, twitchin is a giant polypeptide located in muscle A-bands. The protein kinase of twitchin is autoinhibited by 45 residues upstream (NL) and 60 residues downstream (CRD) of the kinase catalytic core. Molecular dynamics simulation on a twitchin fragment revealed that the NL is released by pulling force. However, it is unclear how the CRD is removed. To identify proteins that may remove the CRD, we performed a yeast two-hybrid screen using twitchin kinase as bait. One interactor is MAK-1, C. elegans orthologue of MAPKAP kinase 2. MAPKAP kinase 2 is phosphorylated and activated by p38 MAP kinase. We demonstrate that the CRD of twitchin is important for binding to MAK-1. mak-1 is expressed in nematode body wall muscle, and antibodies to MAK-1 localize between and around Z-disk analogues and to the edge of A-bands. Whereas unc-22 mutants are completely resistant, mak-1 mutants are partially resistant to nicotine. MAK-1 can phosphorylate twitchin NL-Kin-CRD in vitro. Genetic data suggest the involvement of two other mak-1 paralogues and two orthologues of p38 MAP kinase. These results suggest that MAK-1 is an activator of twitchin kinase and that the p38 MAP kinase pathway may be involved in the regulation of twitchin.

Challenging muscle homeostasis uncovers novel chaperone interactions in Caenorhabditis elegans

Proteome stability is central to cellular function and the lifespan of an organism. This is apparent in muscle cells, where incorrect folding and assembly of the sarcomere contributes to disease and aging. Apart from the myosin-assembly factor UNC-45, the complete network of chaperones involved in assembly and maintenance of muscle tissue is currently unknown. To identify additional factors required for sarcomere quality control, we performed genetic screens based on suppressed or synthetic motility defects in Caenorhabditis elegans. In addition to ethyl methyl sulfonate-based mutagenesis, we employed RNAi-mediated knockdown of candidate chaperones in unc-45 temperature-sensitive mutants and screened for impaired movement at permissive conditions. This approach confirmed the cooperation between UNC-45 and Hsp90. Moreover, the screens identified three novel co-chaperones, CeHop (STI-1), CeAha1 (C01G10.8) and Cep23 (ZC395.10), required for muscle integrity. The specific identification of Hsp90 and Hsp90 co-chaperones highlights the physiological role of Hsp90 in myosin folding. Our work thus provides a clear example of how a combination of mild perturbations to the proteostasis network can uncover specific quality control modules.

Molecular structure of sarcomere-to-membrane attachment at M-Lines in C. elegans muscle

C. elegans is an excellent model for studying nonmuscle cell focal adhesions and the analogous muscle cell attachment structures. In the major striated muscle of this nematode, all of the M-lines and the Z-disk analogs (dense bodies) are attached to the muscle cell membrane and underlying extracellular matrix. Accumulating at these sites are many proteins associated with integrin. We have found that nematode M-lines contain a set of protein complexes that link integrin-associated proteins to myosin thick filaments. We have also obtained evidence for intriguing additional functions for these muscle cell attachment proteins.

The small heat shock protein (sHSP) genes in the silkworm, Bombyx mori, and comparative analysis with other insect sHSP genes

Background

Small heat shock proteins (sHSPs) are products of heat shock response and of other stress responses, and ubiquitous in all three domains of life, archaea, bacteria, and eukarya. They mainly function as molecular chaperones to protect proteins from being denatured in extreme conditions. Study on insect sHSPs could provide some insights into evolution of insects that have adapted to diverse niches in the world.

Results

Taking advantage of the newly assembled genome sequence, we performed a genome-wide analysis of the candidate sHSP genes in the silkworm, Bombyx mori. Based on known silkworm sHSP sequences, we identified 16 silkworm sHSP genes. Most of them are distributed on two silkworm chromosomes 5 and 27, respectively. 15 of 16 silkworm sHSPs have expression evidence. The comparative analysis of insect sHSPs from B. mori, Drosophila melanogaster, Apis mellifera, Tribolium castaneum, and Anopheles gambiae revealed that there is only one orthologous cluster whereas remaining clusters are species-specific on the phylogenetic tree. This suggested that most of sHSPs might have diverged in function across insects investigated. In addition, the data presented in this study also revealed that sHSPs in the insect orthologous cluster are highly conserved in both sequence and expression pattern. In sum, insect sHSPs show a completely different evolutionary pattern from that found in vertebrate sHSPs.

Conclusion

B. mori has the largest number of insect sHSP genes characterized to date, including 16 genes. The inference that most species-specific sHSPs might have diverged in function across insects investigated will help us understand the adaptability of these insects to diverse environments.

ArHsp21, a developmentally regulated small heat-shock protein synthesized in diapausing embryos of Artemia franciscana

Embryos of the crustacean, Artemia franciscana, undergo alternative developmental pathways, producing either larvae or encysted embryos (cysts). The cysts enter diapause, characterized by exceptionally high resistance to environmental stress, a condition thought to involve the sHSP (small heat-shock protein), p26. Subtractive hybridization has revealed another sHSP, termed ArHsp21, in diapause-destined Artemia embryos. ArHsp21 shares sequence similarity with p26 and sHSPs from other organisms, especially in the α-crystallin domain. ArHsp21 is the product of a single gene and its synthesis occurred exclusively in diapause-destined embryos. Specifically, ArHsp21 mRNA appeared 2 days post-fertilization, followed 1 day later by the protein, and then increased until embryo release at day 5. No ArHsp21 protein was detected in embryos developing directly into larvae, although there was a small amount of mRNA at 3 days post-fertilization. The protein was degraded during post-diapause development and had disappeared completely from second instar larvae. ArHsp21 formed large oligomers in encysted embryos and transformed bacteria. When purified from bacteria, ArHsp21 functioned as a molecular chaperone in vitro, preventing heat-induced aggregation of citrate synthase and reduction-driven denaturation of insulin. Sequence characteristics, synthesis patterns and functional properties demonstrate clearly that ArHsp21 is an sHSP able to chaperone other proteins and contribute to stress tolerance during diapause. As such, ArHsp21 would augment p26 chaperone activity and it may also possess novel activities that benefit Artemia embryos exposed to stress.

Thermally induced and developmentally regulated expression of a small heat shock protein in Trichinella spiralis

A cDNA encoding a small heat shock protein of Trichinella spiralis, Ts-sHsp, was cloned and expressed and is herein characterized. This cDNA encoded a predicted protein of 165 amino acids, which had a high sequence identity in alpha crystallin domain with various small heat shock proteins of other organisms. A Western blot analysis indicated that anti-Ts-sHsp recombinant antibody recognized the protein of adults and larvae migrating at about 19 kDa. An in situ localization study showed the protein to be abundantly present in the body wall muscle cells, hypodermis, stichocytes, and esophagus of muscle larvae. The Ts-sHsp recombinant protein possessed chaperone activity to suppress the thermally-induced aggregation of citrate synthase. This sHsp was expressed at various developmental stages of T. spiralis, but at different levels. A high level was observed in mature muscle larvae (infective larvae), which was much higher than the levels seen in adults, newborn larvae, or immature muscle larvae. The expression of the sHsp gene was thermal inducible, thus responding to both cold (0 degrees C) and heat shock (43 degrees C) stress; however, at different patterns. The expression of Ts-sHsp increased gradually from 3 to 72 h after cold stress, while the expression was elevated to its highest after 3 h heat stress and then decreased. These results suggest that this small heat shock protein likely plays a role in the tolerance to both chemical and physical stresses, thereby enhancing the survival ability of Trichinella muscle larvae.

Differential subcellular localization of members of the Toxoplasma gondii small heat shock protein family

The results of this study describe the identification and characterization of the Toxoplasma gondii alpha-crystallin/small heat shock protein (sHsp) family. By database (www.toxodb.org) search, five parasite sHsps (Hsp20, Hsp21, Hsp28, Hsp29, and the previously characterized Hsp30/Bag1) were identified. As expected, they share the homologous alpha-crystallin domain, which is the key characteristic of sHsps. However, the N-terminal segment of each protein contains unique characteristics in size and sequence. Most T. gondii sHsps are constitutively expressed in tachyzoites and fully differentiated bradyzoites, with the exception of Hsp30/Bag1. Interestingly, by subcellular localization we observed that T. gondii sHsps are located in different compartments. Hsp20 is located at the apical end of the cell, Hsp28 is located inside the mitochondrion, Hsp29 showed a membrane-associated labeling, and Hsp21 appeared throughout the cytosol of the parasites. These particular differences in the immunostaining patterns suggest that their targets and functions might be different.

Wrapping the α-Crystallin Domain Fold in a Chaperone Assembly

Small heat shock proteins (sHsps) are oligomers that perform a protective function by binding denatured proteins. Although ubiquitous, they are of variable sequence except for a C-terminal approximately 90-residue "alpha-crystallin domain". Unlike larger stress response chaperones, sHsps are ATP-independent and generally form polydisperse assemblies. One proposed mechanism of action involves these assemblies breaking into smaller subunits in response to stress, before binding unfolding substrate and reforming into larger complexes. Two previously solved non-metazoan sHsp multimers are built from dimers formed by domain swapping between the alpha-crystallin domains, adding to evidence that the smaller subunits are dimers. Here, the 2.5A resolution structure of an sHsp from the parasitic flatworm Taenia saginata Tsp36, the first metazoan crystal structure, shows a new mode of dimerization involving N-terminal regions, which differs from that seen for non-metazoan sHsps. Sequence differences in the alpha-crystallin domains between metazoans and non-metazoans are critical to the different mechanism of dimerization, suggesting that some structural features seen for Tsp36 may be generalized to other metazoan sHsps. The structure also indicates scope for flexible assembly of subunits, supporting the proposed process of oligomer breakdown, substrate binding and reassembly as the chaperone mechanism. It further shows how sHsps can bind coil and secondary structural elements by wrapping them around the alpha-crystallin domain. The structure also illustrates possible roles for conserved residues associated with disease, and suggests a mechanism for the sHsp-related pathogenicity of some flatworm infections. Tsp36, like other flatworm sHsps, possesses two divergent sHsp repeats per monomer. Together with the two previously solved structures, a total of four alpha-crystallin domain structures are now available, giving a better definition of domain boundaries for sHsps.

Constitutive expression of heat shock protein p23 correlates with proneural territories in imaginal discs ofDrosophila melanogaster

2-DE followed by MALDI-TOF was used to purify and identify a Drosophila protein (catalogued as SSP 6002) that showed marked differences in the level of expression in the different imaginal discs of third instar larvae. Fingerprinting showed that the spot of interest was the heat shock 23 polypeptide (hsp23). We characterized the kinetics of its induction by heat shock in wing imaginal discs and raised an antiserum against the denatured protein, which recognizes a single unphosphorylated spot on 2-D gels. The difference in its expression in discs was corroborated by analyzing its level in the imaginal discs of postbithorax mutants. We also investigated the developmental expression of hsp23 in imaginal discs with antiserum raised against the native protein. Its spatial and temporal pattern of expression is related to the proneural territories and maintained even under heat shock conditions. In addition, its pattern of expression is regulated by transcription factors and signaling pathways (notch and epidermal growth factor receptor) involved in proneural specification.

Invertebrate Muscles: Muscle Specific Genes and Proteins

This is the first of a projected series of canonic reviews covering all invertebrate muscle literature prior to 2005 and covers muscle genes and proteins except those involved in excitation-contraction coupling (e.g., the ryanodine receptor) and those forming ligand- and voltage-dependent channels. Two themes are of primary importance. The first is the evolutionary antiquity of muscle proteins. Actin, myosin, and tropomyosin (at least, the presence of other muscle proteins in these organisms has not been examined) exist in muscle-like cells in Radiata, and almost all muscle proteins are present across Bilateria, implying that the first Bilaterian had a complete, or near-complete, complement of present-day muscle proteins. The second is the extraordinary diversity of protein isoforms and genetic mechanisms for producing them. This rich diversity suggests that studying invertebrate muscle proteins and genes can be usefully applied to resolve phylogenetic relationships and to understand protein assembly coevolution. Fully achieving these goals, however, will require examination of a much broader range of species than has been heretofore performed.

Taenia solium: characterization of a small heat shock protein (Tsol-sHSP35.6) and its possible relevance to the diagnosis and pathogenesis of neurocysticercosis

A cDNA encoding for a predicted small heat shock protein (sHSP), Tsol-sfISP35.6, has been isolated by antibody screening of a Taenia solium c-DNA library. The clone was a full-length sequence (1172 bp) with an open reading frame of 945 bp and encoded for a 314 amino acid protein with deduced molecular mass of 35.6 kDa, isoelectric point of 5.6 arid the characteristic HSP20/alpha-crystallin domain duplicated. It was highly conserved, with a high sequence similarity with other platyhelminth sHSPs. Western blot analysis, using serum from neurocysticercosis patients (NCC), indicated that the purified Tsol-sHSP35.6 expression product was immunogenic, while in indirect ELISA, using the purified Tsol-sHSP35.6 expression product as antigen and serum samples from pigs and humans, 80% of T. solium infected pigs and 84% of patients with active, or 71% of patients with inactive NCC were sero-positive. The possible relevance of Tsol-sHSP35.6 in the diagnosis and pathogenesis of NCC is discussed.

Acute p38 MAPK activation decreases force development in ventricular myocytes

Evidence suggests that p38 mitogen-activated protein kinase (MAPK) activation influences cardiac function on an acute basis. The characterization and mechanisms by which this occurs were investigated in the present study. Adult rat ventricular myocytes treated with 1 mM arsenite for 30 min had a 16-fold increase in p38 MAPK phosphorylation that was attenuated by SB-203580 (a p38 MAPK inhibitor). Extracellular signal-regulated protein kinase (ERK) and c-Jun NH2-terminal kinase (JNK) were also minimally activated, but this activation was not sensitive to SB-203580. In addition, arsenite caused a p38 MAPK-independent translocation/activation of protein phosphatase 2a (PP2a) and decrease in phosphorylation of myosin light chain 2 (LC2). Arsenite-p38 MAPK activation led to translocation of heat shock protein 27 but not alpha B-crystallin to the myofilaments. Using isolated cardiomyocytes, we determined that arsenite reduces isometric tension without a change in Ca2+ sensitivity of tension via p38 MAPK and lowers myofibrillar actomyosin Mg2+-ATPase activity in a p38 MAPK-independent manner. Thus arsenite induces a p38 MAPK-independent change in PP2a and LC2 that may account for the arsenite-dependent decrease in ATPase and a p38 MAPK-dependent modification of the myofilaments that decreases myocardial force development.

Expression of the Hsp23 chaperone during Drosophila embryogenesis: association to distinct neural and glial lineages

Background

In addition to their strong induction following stress, small heat shock proteins (Hsp) are also expressed during development in a wide variety of organisms. However, the precise identity of cell(s) expressing these proteins and the functional contribution of small heat shock proteins in such developmental context remain to be determined. The present study provides a detailed description of the Drosophila small heat shock protein Hsp23 expression pattern during embryogenesis and evaluates its functional contribution to central nervous system development.

Results

Throughout embryogenesis, Hsp23 is expressed in a stage-specific manner by a restricted number of neuronal and glial lineages of the central nervous system. Hsp23 is also detected in the amnioserosa and within a single lateral chordotonal organ. Its expression within the MP2 lineage does not require the presence of a functional midline nor the activity of the Notch signaling pathway. Transactivation assays demonstrate that transcription factors implicated in the differentiation of the midline also regulate hsp23 promoter activity. Phenotypic analysis of a transgenic line exhibiting loss of Hsp23 expression in the central nervous system suggests that Hsp23 is not required for development and function of this tissue. Likewise, its overexpression does not cause deleterious effects, as development remains unaffected.

Conclusions

Based on the presented data, we suggest that the tightly regulated developmental expression of Hsp23 is not actively involved in cell differentiation and central nervous system development per se but rather reflects a putative role in preventive "pre-stress" neuroprotection or in non-vital process(es) common to the identified cell lineages.

The sperm outer dense fiber protein is the 10th member of the superfamily of mammalian small stress proteins

Nine proteins have been assigned to date to the superfamily of mammalian small heat shock proteins (sHsps): Hsp27 (HspB1, Hsp25), myotonic dystrophy protein kinase-binding protein (MKBP) (HspB2), HspB3, alphaA-crystallin (HspB4), alphaB-crystallin (HspB5), Hsp20 (p20, HspB6), cardiovascular heat shock protein (cvHsp [HspB7]), Hsp22 (HspB8), and HspB9. The most pronounced structural feature of sHsps is the alpha-crystallin domain, a conserved stretch of approximately 80 amino acid residues in the C-terminal half of the molecule. Using the alpha-crystallin domain of human Hsp27 as query in a BLAST search, we found sequence similarity with another mammalian protein, the sperm outer dense fiber protein (ODFP). ODFP occurs exclusively in the axoneme of sperm cells. Multiple alignment of human ODFP with the other human sHsps reveals that the primary structure of ODFP fits into the sequence pattern that is typical for this protein superfamily: alpha-crystallin domain (conserved), N-terminal domain (less conserved), central region (variable), and C-terminal tails (variable). In a phylogenetic analysis of 167 proteins of the sHsp superfamily, using Bayesian inference, mammalian ODFPs form a clade and are nested within previously identified sHsps, some of which have been implicated in cytoskeletal functions. Both the multiple alignment and the phylogeny suggest that ODFP is the 10th member of the superfamily of mammalian sHsps, and we propose to name it HspB10 in analogy with the other sHsps. The C-terminal tail of HspB10 has a remarkable low-complexity structure consisting of 10 repeats of the motif C-X-P. A BLAST search using the C-terminal tail as query revealed similarity with sequence elements in a number of Drosophila male sperm proteins, and mammalian type I keratins and cornifin-alpha. Taken together, the following findings suggest a specialized role of HspB10 in cytoskeleton: (1) the exclusive location in sperm cell tails, (2) the phylogenetic relationship with sHsps implicated in cytoskeletal functions, and (3) the partial similarity with cytoskeletal proteins.

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

The primary structure of chicken small heat shock protein (sHsp) with apparent molecular weight 25 kDa was refined and it was shown that this protein has conservative primary structure 74RALSRQLSSG(83) at Ser77 and Ser81, which are potential sites of phosphorylation. Recombinant wild-type chicken Hsp25, its three mutants, 1D (S15D), 2D (S77D+S81D) and 3D (S15D+S77D+S81D), as well as delR mutant with the primary structure 74RALS-ELSSG(82) at potential sites of phosphorylation were expressed and purified. It has been shown that the avian tissues contain three forms of Hsp25 having pI values similar to that of the wild-type protein, 1D and 2D mutants that presumably correspond to nonphosphorylated, mono- and di-phosphorylated forms of Hsp25. Recombinant wild-type protein, its 1D mutant and Hsp25, isolated from chicken gizzard, form stable high molecular weight oligomeric complexes. The delR, 2D and 3D mutants tend to dissociate and exist in the form of a mixture of high and low molecular weight oligomers. Point mutations mimicking phoshorylation decrease chaperone activity of Hsp25 measured by reduction of dithiothreitol induced aggregation of alpha-lactalbumin, but increase the chaperone activity of Hsp25 measured by heat induced aggregation of alcohol dehydrogenase. It is concluded that avian Hsp25 has a more stable quaternary structure than its mammalian counterparts and mutations mimicking phosphorylation differently affect chaperone activity of avian Hsp25, depending on the nature of target protein and the way of denaturing.

The lack of chaperonelike activity of Caenorhabditis elegans Hsp12.2 cannot be restored by domain swapping with human alphaB-crystallin

The small heat shock proteins Hsp12.2 and alphaB-crystallin differ in that the former occurs as tetramers, without chaperonelike activity, whereas the latter forms multimers and is a good chaperone. To investigate whether the lack of chaperone activity of Hsp12.2 is primarily due to its tetrameric structure or rather to intrinsic sequence features, we engineered chimeric proteins by swapping the N-terminal, C-terminal, and tail regions of Hsp12.2 and alphaB-crystallin, designated as n-c-t and N-C-T, respectively. Three of the chimeric sHsps, namely N-c-T, n-c-T, and N-C-t, showed nativelike secondary and quaternary structures as measured by circular dichroism and gel permeation chromatography. Combining the conserved alpha-crystallin domain of Hsp12.2 with the N-terminal and tail regions of alphaB-crystallin (N-c-T) resulted in multimeric complexes, but did not restore chaperonelike activity. Replacing the tail region of Hsp12.2 with that of alphaB-crystallin (n-c-T) did not alter the tetrameric structure and lack of chaperone activity. Similarly, providing alphaB-crystallin with the tail of Hsp12.2 (N-C-t) did not substantially influence the multimeric complex size, but it reduced the chaperoning ability, especially for small substrates. These results suggest that the conserved alpha-crystallin domain of Hsp12.2 is intrinsically unsuitable to confer chaperonelike activity and confirms that the tail region in alphaB-crystallin modulates chaperonelike capacity in a substrate-dependent manner.

Characterization of two novel human small heat shock proteins: protein kinase-related HspB8 and testis-specific HspB9

Using search profiles based on the conserved alpha-crystallin domain that is characteristic for small heat shock proteins (sHsps), we traced two new human sHsps. One of these, being the eighth known human sHsp and thus named HspB8, was recently described as a serine-threonine protein kinase (H11), but not identified as an sHsp (C.C. Smith, Y.X. Yu, M. Kulka, L. Aurelian, J. Biol. Chem. 275 (2000)). Northern blotting showed that HspB8/H11 is predominantly transcribed in skeletal muscle and heart, like most other sHsps. The other, named HspB9, is specifically expressed in testis, notably in the spermatogenic cells from late pachytene spermatocyte stage till elongate spermatid stage. While mammalian sHsps are generally highly conserved, mouse HspB9 shows 38% sequence difference with human HspB9, which may confirm its sex-related role.

The expanding family of Arabidopsis thaliana small heat stress proteins and a new family of proteins containing alpha-crystallin domains (Acd proteins)

Comprehensive analysis of the Arabidopsis genome revealed a total of 13 sHsps belonging to 6 classes defined on the basis of their intracellular localization and sequence relatedness plus 6 ORFs encoding proteins distantly related to the cytosolic class Cl or the plastidial class of sHsps. The complexity of the Arabidopsis sHsp family far exceeds that in any other organism investigated to date. Furthermore, we have identified a new family of ORFs encoding multidomain proteins that contain one or more regions with homology to the ACD (Acd proteins). The functions of the Acd proteins and the role of their ACDs remain to be investigated.

Association of several small heat-shock proteins with reproductive tissues in the nematode Caenorhabditis elegans

Immunohistochemical data on 10 of the 14 small heat-shock (smHSPs) proteins in fourth larval stage and adult Caenorhabditis elegans show that the tissues expressing the greatest number of smHSPs are vulva (HSP12s, HSP43 and, under stress, HSP16s) and spermatheca (HSP12s, HSP25, HSP43 and, under stress, HSP16s). HSP43 is also expressed in male tail structures, and following heat-shock HSP16s are expressed in spermatids and spermatozoa.

HSP43, a small heat-shock protein localized to specific cells of the vulva and spermatheca in the nematode Caenorhabditis elegans

Heat-shock protein 43 (HSP43) of Caenorhabditis elegans is prominently expressed in the utse cell, which attaches the uterus to the hypodermis, the uv1 cells joining the vulva and the uterus, the spermathecal valve and junctions between cells of the spermathecal cage. In body-wall muscle, HSP43 forms a punctate pattern of circumferential lines, probably corresponding to regions where the hypodermis contacts the muscle cells.