Small heat-shock proteins regulate membrane lipid polymorphism

HSPB6: A lipid-dependent molecular chaperone inhibits α-synuclein aggregation

The process of protein misfolding and aggregation is associated with various cytotoxic effects. Understanding how this phenomenon is regulated by the protein homeostasis system, however, is difficult, since it takes place through a complex non-linear network of coupled microscopic steps, including primary nucleation, fibril elongation, and secondary nucleation, which depend on environmental factors. To address this problem, we studied how the aggregation of α-synuclein, a protein associated with Parkinson's disease, is modulated by molecular chaperones and lipid membranes. We focused on small heat shock proteins (sHSPs/HSPBs), which interact with proteins and lipids and are upregulated during aging, a major risk factor for protein misfolding diseases. HSPBs act on different microscopic steps to prevent α-synuclein aggregation, with HSPB6 showing a lipid-dependent chaperone activity. Our findings provide an example of how HSPBs diversified their mechanisms of action to reach an efficient regulation of protein misfolding and aggregation within the complex cellular environment.

The role of membrane physiology in sHSP Lo18-lipid interaction and lipochaperone activity

To cope with environmental stresses, organisms, including lactic acid bacteria such as O. oeni, produce stress proteins called HSPs. In wine, O. oeni is constantly confronted by stress affecting its membrane fluidity. To survive through in these deleterious conditions, O. oeni synthesizes Lo18, a unique, small HSP which acts as a molecular chaperone and a lipochaperone. The molecular mechanism underlying its lipochaperone activity, particularly regarding membrane lipid composition, remains poorly understood. In this context, Lo18 lipochaperone activity and the associated modification in protein structure were studied during interaction with different liposomes from O. oeni cultures representing unstressed, stressed and stressed-adapted physiological states. The results showed that the presence of the membrane (whatever its nature) induces a modification of Lo18's structure. Also, the presence of oleic acid and/or phosphatidylglycerol is important to favor Lo18-membrane interaction, allowing lipochaperone activity. This research enhances understanding of sHSP-membrane interactions in bacterial systems.

The small heat shock protein Hsp20.8 imparts tolerance to high temperatures in the leafminer fly, Liriomyza trifolii (Diptera: Agtomyzidae)

As an environmental factor, temperature impacts the distribution of species and influences interspecific competition. The molecular chaperones encoded by small heat shock proteins (sHsps) are essential for rapid, appropriate responses to environmental stress. This study focuses on Hsp20.8, which encodes a temperature-responsive sHsp in Liriomyza trifolii, an insect pest that infests both agricultural and ornamental crops. Hsp20.8 expression was highest at 39℃ in L. trifolii pupae and adults, and expression levels were greater in pupae than in adults. Recombinant Hsp20.8 was expressed in Escherichia coli and conferred a higher survival rate than the empty vector to bacterial cells exposed to heat stress. RNA interference experiments were conducted using L. trifolii adults and prepupae and the knockdown of Hsp20.8 expression increased mortality in L. trifolii during heat stress. The results expand our understanding of sHsp function in Liriomyza spp. and the ongoing adaptation of this pest to climate change. In addition, this study is also important for predicting the distribution of invasive species and proposing new prevention and control strategies based on temperature adaptation.

Association of Alpha-Crystallin with Human Cortical and Nuclear Lens Lipid Membrane Increases with the Grade of Cortical and Nuclear Cataract

Eye lens α-crystallin has been shown to become increasingly membrane-bound with age and cataract formation; however, to our knowledge, no studies have investigated the membrane interactions of α-crystallin throughout the development of cataracts in separated cortical membrane (CM) and nuclear membrane (NM) from single human lenses. In this study, four pairs of human lenses from age-matched male and female donors and one pair of male lenses ranging in age from 64 to 73 years old (yo) were obtained to investigate the interactions of α-crystallin with the NM and CM throughout the progression of cortical cataract (CC) and nuclear cataract (NC) using the electron paramagnetic resonance spin-labeling method. Donor health history information (diabetes, smoker, hypertension, radiation treatment), sex, and race were included in the data analysis. The right eye lenses CM and NM investigated were 64 yo male (CC: 0), 68 yo male (CC: 3, NC: 2), 73 yo male (CC: 1, NC: 2), 68 yo female (CC: 3, NC: 2), and 73 yo female (CC: 1, NC: 3). Similarly, left eye lenses CM and NM investigated were 64 yo male (CC: 0), 68 yo male (CC: 3, NC: 2), 73 yo male (CC: 2, NC: 3), 68 yo female (CC: 3, NC: 2), and 73 yo female (CC: 1, NC: 3). Analysis of α-crystallin binding to male and female eye lens CM and NM revealed that the percentage of membrane surface occupied (MSO) by α-crystallin increases with increasing grade of CC and NC. The binding of α-crystallin resulted in decreased mobility, increased order, and increased hydrophobicity on the membrane surface in male and female eye lens CM and NM. CM mobility decreased with an increase in cataracts for both males and females, whereas the male lens NM mobility showed no significant change, while female lens NM showed increased mobility with an increase in cataract grade. Our data shows that a 68 yo female donor (long-term smoker, pre-diabetic, and hypertension; grade 3 CC) showed the largest MSO by α-crystallin in CM from both the left and right lens and had the most pronounced mobility changes relative to all other analyzed samples. The variation in cholesterol (Chol) content, size and amount of cholesterol bilayer domains (CBDs), and lipid composition in the CM and NM with age and cataract might result in a variation of membrane surface mobility, membrane surface hydrophobicity, and the interactions of α-crystallin at the surface of each CM and NM. These findings provide insight into the effect of decreased Chol content and the reduced size and amount of CBDs in the cataractous CM and NM with an increased binding of α-crystallin with increased CC and NC grade, which suggests that Chol and CBDs might be a key component in maintaining lens transparency.

The response of heat shock proteins in honey bees to abiotic and biotic stressors

Honey bees, Apis mellifera, are the most important managed pollinators worldwide. They are highly impacted by various abiotic and biotic stressors, especially temperature extremes, which can lead to cellular damage and death. The induction of heat shock proteins (HSPs) has been recorded in honey bees as a response to various types of stressors. HSPs are classified into different gene families according to their molecular weights. HSPs play an important role in maintaining cellular protein homeostasis due to their contribution as molecular chaperones or co-chaperones. HSPs in honey bees have complex functions with induction even under normal colony conditions. Previous studies have suggested various functions of HSPs to protect cells from damage under exposure to environmental stressors, pollutants, and pathogens. Surprisingly, HSPs have also been found to play roles in larval development and age-related tasks. The expression of HSPs varies depending on tissue type, developmental stage, age, and stress period. This article reviews studies on HSPs (sHSPs, HSP40, HSP60, HSP70, and HSP90) in honey bees and highlights gaps in the available knowledge. This review is crucial for honey bee research, particularly in the face of climate change challenges.

Various tomato cultivars display contrasting morphological and molecular responses to a chronic heat stress

Climate change is one of the biggest threats that human society currently needs to face. Heat waves associated with global warming negatively affect plant growth and development and will increase in intensity and frequency in the coming years. Tomato is one of the most produced and consumed fruit in the world but remarkable yield losses occur every year due to the sensitivity of many cultivars to heat stress (HS). New insights into how tomato plants are responding to HS will contribute to the development of cultivars with high yields under harsh temperature conditions. In this study, the analysis of microsporogenesis and pollen germination rate of eleven tomato cultivars after exposure to a chronic HS revealed differences between genotypes. Pollen development was either delayed and/or desynchronized by HS depending on the cultivar considered. In addition, except for two, pollen germination was abolished by HS in all cultivars. The transcriptome of floral buds at two developmental stages (tetrad and pollen floral buds) of five cultivars revealed common and specific molecular responses implemented by tomato cultivars to cope with chronic HS. These data provide valuable insights into the diversity of the genetic response of floral buds from different cultivars to HS and may contribute to the development of future climate resilient tomato varieties.

Hyperthermia Enhances Adeno-Associated Virus Vector Transduction Efficiency in Melanoma Cells

Gene therapy perfectly fits in the current needs of medicine for patients with melanoma. One of the major challenges of gene therapy is to increase gene transfer. The role of hyperthermia in the improvement of AAV (adeno-associated virus) transduction efficiency has been indicated. The aim of the present study was to assess the transduction efficacy of melanoma cell lines (A375, G-361, and SK-MEL-1) with the use of the rAAV/DJ mosaic vector under hyperthermia conditions. The analysis of changes in the transduction efficacy and expression of HSPs (heat shock proteins) and receptors for AAV was performed. The transduction was performed at 37 °C and at 43 °C (1 h). Hyperthermia enhanced gene transfer in all the tested cell lines. The most efficient transducing cell line under hyperthermia was A375 (increase by 17%). G361 and SK-MEL-1 cells showed an increase of 7%. The changes in the expression of the AAV receptors and HSPs after hyperthermia were observed. A key role in the improvement of gene transfer may be played by AAVR, HSPB1, HSP6, DNAJC4, HSPD1, HSPA8, HSPA9, HSP90AB1, and AHSA1. This study showed the possibility of the use of hyperthermia as a factor enabling the stimulation of cell transduction with rAAV vectors, thereby providing tools for the improvement in the efficacy of gene therapy based on rAAV.

Influence of temperature variation on gene expression and cocoon production in Bombyx mori Linnaeus, 1758 (Lepidoptera: Bombycidae)

Silkworms (Bombyx mori) are lepidopterans of economic importance for global silk production. However, factors that directly affect the yield and quality of silkworm cocoon production, such as diseases and temperature fluctuations, cause great economic losses. Knowing how they respond to rearing temperature during the most critical stage of their life cycle (i.e., fifth instar) could provide information on their adaptation and improve silk production. In the current work, we analyzed transcriptional data from two groups of B. mori that were reared at 26 °C and 34 °C throughout the fifth instar. The silkworms and cocoons were weighed. In total, 3115 transcripts were differentially expressed (DE; including 1696 down-regulated and 1419 up-regulated) among the 29,157 sequences found by transcriptome assembly. We emphasize the genes associated with immunological response, transcription factors, silk biosynthesis, and heat shock proteins, among the DE transcripts in response to the temperature conditions. Silkworms reared at 34 °C presented a reduced mean body weight (-0.944 g in comparison to the 26 °C group), which had a direct impact on the weight of cocoons formed and the silk conversion rate. These changes were statistically significant when compared to silkworms reared at 26 °C. Mortality rates (6 and 9 %, at 26 °C and 34 °C, respectively) were similar to those obtained in breeding fields. The findings provide information on the biological processes involved in the temperature response mechanism of silkworms, as well as information that may be used in future climatization processes at rearing facilities and in breeding for improved thermotolerance.

Impact of heat priming on heat shock responses in Origanum vulgare: Enhanced foliage photosynthetic tolerance and biphasic emissions of volatiles

Climate change enhances the frequency of heatwaves that negatively affect photosynthesis and can alter constitutive volatile emissions and elicit emissions of stress volatiles, but how pre-exposure to mildly warmer temperatures affects plant physiological responses to subsequent severe heat episodes remains unclear, especially for aromatic plants with high and complex volatile defenses. We studied the impact of heat shock (45 °C/5 min) applied alone and after exposure to moderate heat stress (35 °C/1 h, priming) on foliage photosynthesis and volatile emissions in the aromatic plant Origanum vulgare through 72 h recovery period. Heat stress decreased photosynthesis rates and stomatal conductance, whereas the reductions in photosynthesis were primarily due to non-stomatal factors. In non-primed plants, heat shock-induced reductions in photosynthetic activity were the greatest, but photosynthetic activity completely recovered by the end of the experiment. In primed plants, a certain inhibition of photosynthetic activity remained, suggesting a sustained priming effect. Heat shock enhanced the emissions of volatiles including lipoxygenase pathway volatiles, long-chained fatty acid-derived compounds, mono- and sesquiterpenes, geranylgeranyl diphosphate pathway volatiles, and benzenoids, whereas different heat treatments resulted in unique emission blends. In non-primed plants, stress-elicited emissions recovered at 72 h. In primed plants, volatile emissions were multiphasic, the first phase, between 0.5 and 10 h, reflected the primary stress response, whereas the secondary rise, between 24 and 72 h, indicated activations of different defense metabolic pathways. Our results demonstrate that exposure to mild heat leads to a sustained physiological stress memory that enhances plant resistance to subsequent severe heat stress episodes.

Expression of the gonad-specific small heat shock protein, CfHSP20.2, in the spruce budworm, Choristoneura fumiferana (Clem.)

Small heat shock proteins (sHSPs) play important roles in insect development and stress resistance. However, the in vivo functions and mechanisms of action remain largely unknown or unclear for most members of the sHSPs in insects. This study investigated the expression of CfHSP20.2 in the spruce budworm, Choristoneura fumiferana (Clem.) under normal and heat-stress conditions. Under normal conditions, CfHSP20.2 transcript and protein were highly and constantly expressed in the testes of male larvae, pupae and young adults and in the ovaries of female late-stage pupae and adults. After adult eclosion, CfHSP20.2 remained highly and almost constantly expressed in the ovaries, but in contrast, was downregulated in the testes. Upon heat stress, CfHSP20.2 was upregulated in the gonads and non-gonadal tissues in both sexes. These results indicate that CfHSP20.2 expression is gonad-specific and heat-inducible. This provides evidence that the CfHSP20.2 protein plays important roles during reproductive development under normal environmental conditions, while under heat-stress conditions, it may also enhance the thermal tolerance of the gonads and non-gonadal tissues.

Tardigrade small heat shock proteins can limit desiccation-induced protein aggregation

Small heat shock proteins (sHSPs) are chaperones with well-characterized roles in heat stress, but potential roles for sHSPs in desiccation tolerance have not been as thoroughly explored. We identified nine sHSPs from the tardigrade Hypsibius exemplaris, each containing a conserved alpha-crystallin domain flanked by disordered regions. Many of these sHSPs are highly expressed. Multiple tardigrade and human sHSPs could improve desiccation tolerance of E. coli, suggesting that the capacity to contribute to desicco-protection is a conserved property of some sHSPs. Purification and subsequent analysis of two tardigrade sHSPs, HSP21 and HSP24.6, revealed that these proteins can oligomerize in vitro. These proteins limited heat-induced aggregation of the model enzyme citrate synthase. Heterologous expression of HSP24.6 improved bacterial heat shock survival, and the protein significantly reduced heat-induced aggregation of soluble bacterial protein. Thus, HSP24.6 likely chaperones against protein aggregation to promote heat tolerance. Furthermore, HSP21 and HSP24.6 limited desiccation-induced aggregation and loss of function of citrate synthase. This suggests a mechanism by which tardigrade sHSPs promote desiccation tolerance, by limiting desiccation-induced protein aggregation, thereby maintaining proteostasis and supporting survival. These results suggest that sHSPs provide a mechanism of general stress resistance that can also be deployed to support survival during anhydrobiosis.

Fine Tuning of ROS, Redox and Energy Regulatory Systems Associated with the Functions of Chloroplasts and Mitochondria in Plants under Heat Stress

Heat stress severely affects plant growth and crop production. It is therefore urgent to uncover the mechanisms underlying heat stress responses of plants and establish the strategies to enhance heat tolerance of crops. The chloroplasts and mitochondria are known to be highly sensitive to heat stress. Heat stress negatively impacts on the electron transport chains, leading to increased production of reactive oxygen species (ROS) that can cause damages on the chloroplasts and mitochondria. Disruptions of photosynthetic and respiratory metabolisms under heat stress also trigger increase in ROS and alterations in redox status in the chloroplasts and mitochondria. However, ROS and altered redox status in these organelles also activate important mechanisms that maintain functions of these organelles under heat stress, which include HSP-dependent pathways, ROS scavenging systems and retrograde signaling. To discuss heat responses associated with energy regulating organelles, we should not neglect the energy regulatory hub involving TARGET OF RAPAMYCIN (TOR) and SNF-RELATED PROTEIN KINASE 1 (SnRK1). Although roles of TOR and SnRK1 in the regulation of heat responses are still unknown, contributions of these proteins to the regulation of the functions of energy producing organelles implicate the possible involvement of this energy regulatory hub in heat acclimation of plants.

Is the lipochaperone activity of sHSP a key to the stress response encoded in its primary sequence?

Several strategies have been put in place by organisms to adapt to their environment. One of these strategies is the production of stress proteins such as sHSPs, which have been widely described over the last 30 years for their role as molecular chaperones. Some sHSPs have, in addition, the particularity to exert a lipochaperone role by interacting with membrane lipids to maintain an optimal membrane fluidity. However, the mechanisms involved in this sHSP-lipid interaction remain poorly understood and described rather sporadically in the literature. This review gathers the information concerning the structure and function of these proteins available in the literature in order to highlight the mechanism involved in this interaction. In addition, analysis of primary sequence data of sHSPs available in database shows that sHSPs can interact with lipids via certain amino acid residues present on some β sheets of these proteins. These residues could have a key role in the structure and/or oligomerization dynamics of sHPSs, which is certainly essential for interaction with membrane lipids and consequently for maintaining optimal cell membrane fluidity.

Molecular chaperone function of three small heat-shock proteins from a model probiotic species

Small heat-shock proteins (sHSP) are ubiquitous ATP-independent chaperones that prevent irreversible aggregation of heat-damaged denaturing proteins. Lactiplantibacillus plantarum is a widespread Gram-positive bacterium with probiotic claims and vast potential for agro-food, biotechnological and biomedical applications. L. plantarum possesses a family of three sHSP, which were previously demonstrated to be involved in its stress tolerance mechanisms. Here, the three L. plantarum sHSP were heterologously expressed, purified and shown to have a chaperone activity in vitro, measuring their capacity to suppress protein aggregation, as assayed spectrophotometrically by light scattering. Their anti-aggregative capacity was found to be differently influenced by pH. Differences were also found relative to their holdase function and their capacity to modulate liposome membrane fluidity, suggesting interplays between them and indicating diversified activities. This is the first study assessing the chaperone action of sHSP from a probiotic model. The different roles of the three sHSP can increase L. plantarum's capabilities to survive the various types of stress characterising the diverse habitats of this highly adaptable species. Reported evidence supports the interest in L. plantarum as one of the model species for bacteria that have three different sHSP-encoding genes in their genomes.

The molecular basis for pore pattern morphogenesis in diatom silica

Biomineral-forming organisms produce inorganic materials with complex, genetically encoded morphologies that are unmatched by current synthetic chemistry. It is poorly understood which genes are involved in biomineral morphogenesis and how the encoded proteins guide this process. We addressed these questions using diatoms, which are paradigms for the self-assembly of hierarchically meso- and macroporous silica under mild reaction conditions. Proteomics analysis of the intracellular organelle for silica biosynthesis led to the identification of new biomineralization proteins. Three of these, coined dAnk1-3, contain a common protein-protein interaction domain (ankyrin repeats), indicating a role in coordinating assembly of the silica biomineralization machinery. Knocking out individual dank genes led to aberrations in silica biogenesis that are consistent with liquid-liquid phase separation as underlying mechanism for pore pattern morphogenesis. Our work provides an unprecedented path for the synthesis of tailored mesoporous silica materials using synthetic biology.

SlHSP17.7 Ameliorates Chilling Stress-Induced Damage by Regulating Phosphatidylglycerol Metabolism and Calcium Signal in Tomato Plants

Tomatoes (Solanum lycopersicum L.) are sensitive to chilling temperatures between 0 °C and 12 °C owing to their tropical origin. SlHSP17.7, a cytoplasmic heat shock protein, interacts with cation/calcium exchanger 1-like (SlCCX1-like) protein and promotes chilling tolerance in tomato fruits (Zhang, et al., Plant Sci., 2020, 298, 1-12). The overexpression of SlHSP17.7 can also promote cold tolerance in tomato plants, but its specific mechanism remains unclear. In this study, we show that the overexpression of SlHSP17.7 in tomato plants enhances chilling tolerance with better activity of photosystem II (PSII). Metabolic analyses revealed that SlHSP17.7 improved membrane fluidity by raising the levels of polyunsaturated fatty acids. Transcriptome analyses showed that SlHSP17.7 activated Ca2+ signaling and induced the expression of C-repeat binding factor (CBF) genes, which in turn inhibited the production of reactive oxygen species (ROS). The gene coexpression network analysis showed that SlHSP17.7 is coexpressed with SlMED26b. SlMED26b silencing significantly lowered OE-HSP17.7 plants' chilling tolerance. Thus, SlHSP17.7 modulates tolerance to chilling via both membrane fluidity and Ca2+-mediated CBF pathway in tomato plants.

The Small Heat Shock Protein, HSPB1, Interacts with and Modulates the Physical Structure of Membranes

Small heat shock proteins (sHSPs) have been demonstrated to interact with lipids and modulate the physical state of membranes across species. Through these interactions, sHSPs contribute to the maintenance of membrane integrity. HSPB1 is a major sHSP in mammals, but its lipid interaction profile has so far been unexplored. In this study, we characterized the interaction between HSPB1 and phospholipids. HSPB1 not only associated with membranes via membrane-forming lipids, but also showed a strong affinity towards highly fluid membranes. It participated in the modulation of the physical properties of the interacting membranes by altering rotational and lateral lipid mobility. In addition, the in vivo expression of HSPB1 greatly affected the phase behavior of the plasma membrane under membrane fluidizing stress conditions. In light of our current findings, we propose a new function for HSPB1 as a membrane chaperone.

Alpha-Crystallin-Membrane Association Modulated by Phospholipid Acyl Chain Length and Degree of Unsaturation

α-crystallin-membrane association increases with age and cataracts, with the primary association site of α-crystallin being phospholipids. However, it is unclear if phospholipids’ acyl chain length and degree of unsaturation influence α-crystallin association. We used the electron paramagnetic resonance approach to investigate the association of α-crystallin with phosphatidylcholine (PC) membranes of different acyl chain lengths and degrees of unsaturation and with and without cholesterol (Chol). The association constant (Ka) of α-crystallin follows the trends, i.e., Ka (14:0−14:0 PC) > Ka (18:0−18:1 PC) > Ka (18:1−18:1 PC) ≈ Ka (16:0−20:4 PC) where the presence of Chol decreases Ka for all membranes. With an increase in α-crystallin concentration, the saturated and monounsaturated membranes rapidly become more immobilized near the headgroup regions than the polyunsaturated membranes. Our results directly correlate the mobility and order near the headgroup regions of the membrane with the Ka, with the less mobile and more ordered membrane having substantially higher Ka. Furthermore, our results show that the hydrophobicity near the headgroup regions of the membrane increases with the α-crystallin association, indicating that the α-crystallin-membrane association forms the hydrophobic barrier to the transport of polar and ionic molecules, supporting the barrier hypothesis in cataract development.

Understanding Diversity, Evolution, and Structure of Small Heat Shock Proteins in Annelida Through in Silico Analyses

Small heat shock proteins (sHsps) are oligomeric stress proteins characterized by an α-crystallin domain (ACD). These proteins are localized in different subcellular compartments and play critical roles in the stress physiology of tissues, organs, and whole multicellular eukaryotes. They are ubiquitous proteins found in all living organisms, from bacteria to mammals, but they have never been studied in annelids. Here, a data set of 23 species spanning the annelid tree of life, including mostly transcriptomes but also two genomes, was interrogated and 228 novel putative sHsps were identified and manually curated. The analysis revealed very high protein diversity and showed that a significant number of sHsps have a particular dimeric architecture consisting of two tandemly repeated ACDs. The phylogenetic analysis distinguished three main clusters, two of them containing both monomeric sHsps, and ACDs located downstream in the dimeric sHsps, and the other one comprising the upstream ACDs from those dimeric forms. Our results support an evolutionary history of these proteins based on duplication events prior to the Spiralia split. Monomeric sHsps 76) were further divided into five subclusters. Physicochemical properties, subcellular location predictions, and sequence conservation analyses provided insights into the differentiating elements of these putative functional groups. Strikingly, three of those subclusters included sHsps with features typical of metazoans, while the other two presented characteristics resembling non-metazoan proteins. This study provides a solid background for further research on the diversity, evolution, and function in the family of the sHsps. The characterized annelid sHsps are disclosed as essential for improving our understanding of this important family of proteins and their pleotropic functions. The features and the great diversity of annelid sHsps position them as potential powerful molecular biomarkers of environmental stress for acting as prognostic tool in a diverse range of environments.

Alpha-Crystallin Association with the Model of Human and Animal Eye Lens-Lipid Membranes is Modulated by Surface Hydrophobicity of Membranes

PURPOSE

This research aims to probe the interaction of α-crystallin with a model of human, porcine, and mouse lens-lipid membranes.

METHODS

Cholesterol/model of human lens-lipid (Chol/MHLL), cholesterol/model of porcine lens-lipid (Chol/MPLL), and cholesterol/model of mouse lens-lipid (Chol/MMLL) membranes with 0 to 60 mol% Chol were prepared using the rapid solvent exchange method and probe-tip sonication. The hydrophobicity near the surface of model lens-lipid membranes and α-crystallin association with these membranes were investigated using the electron paramagnetic resonance spin-labeling approach.

RESULTS

With increased Chol content, the hydrophobicity near the surface of Chol/MHLL, Chol/MPLL, and Chol/MMLL membranes, the maximum percentage of membrane surface occupied (MMSO) by α-crystallin, and the association constant (K_a) decreased, showing that surface hydrophobicity of model lens-lipid membranes modulated the α-crystallin association with these membranes. The different MMSO and K_a for different model lens-lipid membranes with different rates of decrease of MMSO and K_a with increased Chol content and decreased hydrophobicity near the surface of these membranes suggested that the lipid composition also modulates α-crystallin association with membranes. Despite different lipid compositions, complete inhibition of α-crystallin association with model lens-lipid membranes was observed at saturating Chol content forming cholesterol bilayer domains (CBDs) with the lowest hydrophobicity near the surface of these membranes. The decreased mobility parameter with increased α-crystallin concentration suggested that membranes near the surface became less mobile due to α-crystallin association. The decreased mobility parameter and increased maximum splitting with increased Chol content suggested that membranes became less mobile and more ordered near the surface with increased Chol content.

CONCLUSIONS

This study suggested that the interaction of α-crystallin with model lens-lipid membranes is hydrophobic. Furthermore, our data indicated that Chol and CBDs reduce α-crystallin association with lens membrane, likely increase α-crystallin concentration in lens cytoplasm, and possibly favor the chaperone-like activity of α-crystallin maintaining lens cytoplasm homeostasis.

FTSH4 and OMA1 mitochondrial proteases reduce moderate heat stress-induced protein aggregation

The threat of global warming makes uncovering mechanisms of plant tolerance to long-term moderate heat stress particularly important. We previously reported that Arabidopsis (Arabidopsis thaliana) plants lacking mitochondrial proteases FTSH4 or OMA1 suffer phenotypic changes under long-term stress of 30°C, while their growth at 22°C is not affected. Here we found that these morphological and developmental changes are associated with increased accumulation of insoluble mitochondrial protein aggregates that consist mainly of small heat-shock proteins (sHSPs). Greater accumulation of sHSPs in ftsh4 than oma1 corresponds with more severe phenotypic abnormalities. We showed that the proteolytic activity of FTSH4, and to a lesser extent of OMA1, as well as the chaperone function of FTSH4, is crucial for protecting mitochondrial proteins against aggregation. We demonstrated that HSP23.6 and NADH dehydrogenase subunit 9 present in aggregates are proteolytic substrates of FTSH4, and this form of HSP23.6 is also a substrate of OMA1 protease. In addition, we found that the activity of FTSH4 plays an important role during recovery from elevated to optimal temperatures. Isobaric tags for relative and absolute quantification (iTRAQ)-based proteomic analyses, along with identification of aggregation-prone proteins, implicated mitochondrial pathways affected by protein aggregation (e.g. assembly of complex I) and revealed that the mitochondrial proteomes of ftsh4 and oma1 plants are similarly adapted to long-term moderate heat stress. Overall, our data indicate that both FTSH4 and OMA1 increase the tolerance of plants to long-term moderate heat stress by reducing detergent-tolerant mitochondrial protein aggregation.

The interaction of heat shock proteins with cellular membranes: a historical perspective

The interaction of heat shock proteins (HSP) with cellular membranes has been an enigmatic process, initially observed by morphological studies, inferred during the purification of HSP70s, and confirmed after the detection of these proteins on the surface of cancer cells and their insertion into artificial lipid bilayers. Today, the association of several HSP with lipid membranes is well established. However, the mechanisms for membrane insertion have been elusive. There is conclusive evidence indicating that HSP70s have a great selectivity for negatively charged phospholipids, whereas other HSP have a broader spectrum of lipid specificity. HSP70 also oligomerizes upon membrane insertion, forming ion conductance channels. The functional role of HSP70 lipid interactions appears related to membrane stabilization that may play a role during cell membrane biogenesis. They could also play a role as membrane chaperones as well as during endocytosis, microautophagy, and signal transduction. Moreover, HSP membrane association is a key component in the extracellular export of these proteins. The presence of HSP70 on the surface of cancer cells and its interaction with lysosome membranes have been envisioned as potential therapeutic targets. Thus, the biology and function of HSP membrane association are reaching a new level of excitement. This review is an attempt to preserve the recollection of the pioneering contributions of many investigators that have participated in this endeavor.

Characterization and functional analysis of Cshsp19.0 encoding a small heat shock protein in Chilo suppressalis (Walker)

Small heat shock proteins (sHSPs) function as ATP-independent chaperones that preserve cellular proteostasis under stressful conditions. In this study, Cshsp19.0, which encodes a new small heat shock protein, was isolated and characterized from Chilo suppressalis (Walker) to better understand the contribution of sHSPs to insect development and stress tolerance. The full-length Cshsp19.0 cDNA was 697 bp and encoded a 19.0 kDa protein with an isoelectric point of 5.95. Phylogenetic analysis and amino acid alignments indicated that Cshsp19.0 is a member of the sHSP family. Cshsp19.0 was expressed at maximal levels in foreguts and showed the least amount of expression in fat bodies. Expression analysis in different developmental stages of C. suppressalis revealed that Cshsp19.0 was most highly expressed in 1st instar larvae. Furthermore, Cshsp19.0 was upregulated when insects were exposed to heat and cold stress for a 2-h period. There were significant differences in the male and female pupae in response to humidity; Cshsp19.0 expression increased in male pupae as RH increased, whereas the inverse pattern was observed in female pupae. Larvae exhibited a lower rate of survival when Cshsp19.0 was silenced by a nanomaterial-promoted RNAi method. The results confirm that Cshsp19.0 functions to increase environmental stress tolerance and regulates physiological activities in C. suppressalis.

Investigation of the antidepressant mechanism of combined Radix Bupleuri and Radix Paeoniae Alba treatment using proteomics analysis of liver tissue

Depression is a chronic, common mental illness characterized by depressed mood, anxiety, insomnia, cognitive impairment, and even suicidal tendency. In traditional Chinese medicine theory, the cause of depression is deemed to be "stagnation of liver qi". So relieving "stagnation of liver qi" is effective for depression. The combination of Radix Bupleuri and Radix Paeoniae Alba, which is used to soothe the liver and relieve depression, has antidepressant effects, but the mechanisms of the effects are still unclear. In this study, a rat model of chronic unpredictable mild stress was established as a model of depression, and proteomics analysis was used to explore the potential mechanisms of this combination in alleviating depression. Biological information analysis was performed on the selected differential proteins, and the enriched pathways mainly included the Jak-STAT signaling pathway, valine, leucine, and isoleucine degradation, and oxidative phosphorylation. The expression of key proteins included metallothionein-1, cyclin-dependent kinase, ubiquitin carboxyl-terminal hydrolase-1, and Cryab was further verified by western blotting, and the results which were consistent with the proteomics results, confirmed the reliability of the proteomic analysis. The antidepressant mechanism of combined Radix Bupleuri and Radix Paeoniae Alba treatment may be related to the oxidative stress response, neuroplasticity, the immune response, and neuroprotection.

Hot topic: Thermosensing in plants

Plants alter their morphology and cellular homeostasis to promote resilience under a variety of heat regimes. Molecular processes that underlie these responses have been intensively studied and found to encompass diverse mechanisms operating across a broad range of cellular components, timescales and temperatures. This review explores recent progress throughout this landscape with a particular focus on thermosensing in the model plant Arabidopsis. Direct temperature sensors include the photosensors phytochrome B and phototropin, the clock component ELF3 and an RNA switch. In addition, there are heat-regulated processes mediated by ion channels, lipids and lipid-modifying enzymes, taking place at the plasma membrane and the chloroplast. In some cases, the mechanism of temperature perception is well understood but in others, this remains an open question. Potential novel thermosensing mechanisms are based on lipid and liquid-liquid phase separation. Finally, future research directions of high temperature perception and signalling pathways are discussed.

Association of Alpha-Crystallin with Fiber Cell Plasma Membrane of the Eye Lens Accompanied by Light Scattering and Cataract Formation

α-crystallin is a major protein found in the mammalian eye lens that works as a molecular chaperone by preventing the aggregation of proteins and providing tolerance to stress in the eye lens. These functions of α-crystallin are significant for maintaining lens transparency. However, with age and cataract formation, the concentration of α-crystallin in the eye lens cytoplasm decreases with a corresponding increase in the membrane-bound α-crystallin, accompanied by increased light scattering. The purpose of this review is to summarize previous and recent findings of the role of the: (1) lens membrane components, i.e., the major phospholipids (PLs) and sphingolipids, cholesterol (Chol), cholesterol bilayer domains (CBDs), and the integral membrane proteins aquaporin-0 (AQP0; formally MIP26) and connexins, and (2) α-crystallin mutations and post-translational modifications (PTMs) in the association of α-crystallin to the eye lens's fiber cell plasma membrane, providing thorough insights into a molecular basis of such an association. Furthermore, this review highlights the current knowledge and need for further studies to understand the fundamental molecular processes involved in the association of α-crystallin to the lens membrane, potentially leading to new avenues for preventing cataract formation and progression.

Advances in Understanding of Desiccation Tolerance of Lichens and Lichen-Forming Algae

Lichens are symbiotic associations (holobionts) established between fungi (mycobionts) and certain groups of cyanobacteria or unicellular green algae (photobionts). This symbiotic association has been essential in the colonization of terrestrial dry habitats. Lichens possess key mechanisms involved in desiccation tolerance (DT) that are constitutively present such as high amounts of polyols, LEA proteins, HSPs, a powerful antioxidant system, thylakoidal oligogalactolipids, etc. This strategy allows them to be always ready to survive drastic changes in their water content. However, several studies indicate that at least some protective mechanisms require a minimal time to be induced, such as the induction of the antioxidant system, the activation of non-photochemical quenching including the de-epoxidation of violaxanthin to zeaxanthin, lipid membrane remodeling, changes in the proportions of polyols, ultrastructural changes, marked polysaccharide remodeling of the cell wall, etc. Although DT in lichens is achieved mainly through constitutive mechanisms, the induction of protection mechanisms might allow them to face desiccation stress in a better condition. The proportion and relevance of constitutive and inducible DT mechanisms seem to be related to the ecology at which lichens are adapted to.

iTRAQ-based proteomic analysis of duck muscle related to lipid oxidation

Lipid oxidation is the main cause of quality deterioration in meat and meat products. To facilitate the identification of candidate molecular biomarkers that are linked to lipid oxidation, we performed the proteomic analysis of duck muscle using isobaric tag for relative and absolute quantification (iTRAQ), followed by parallel reaction monitoring (PRM) to confirm the iTRAQ results. Pectoralis major muscles were divided into 2 groups in accordance with lipid oxidation, and iTRAQ-based analysis identified a total of 301 differentially expressed proteins, of which 15 proteins were examined by PRM assay. Proteins involved in lipid binding and metabolism, lipolysis, stress response, oxidative respiratory chain, and redox regulation were found to be differentially expressed between 2 groups and might affect lipid oxidation in muscles. The findings could contribute to the improved understanding of key proteins and processes engaged in lipid oxidation of meat.

Mitochondrial Small Heat Shock Proteins Are Essential for Normal Growth of Arabidopsis thaliana

Mitochondria play important roles in the plant stress responses and the detoxification of the reactive oxygen species generated in the electron transport chain. Expression of genes encoding stress-related proteins such as the mitochondrial small heat shock proteins (M-sHSP) is upregulated in response to different abiotic stresses. In Arabidopsis thaliana, three M-sHSPs paralogous genes were identified, although their function under physiological conditions remains elusive. The aim of this work is to uncover the in vivo function of all three M-sHSPs at the whole plant level. To accomplish this goal, we analyzed the phenotype, proteomic, and metabolic profiles of Arabidopsis knock-down lines of M-sHSPs (single, double, and triple knock-down lines) during normal plant growth. The triple knock-down plants showed the most prominent altered phenotype at vegetative and reproductive stages without any externally applied stress. They displayed chlorotic leaves, growth arrest, and low seed production. Concomitantly, they exhibited increased levels of sugars, proline, and citric, malic, and ascorbic acid, among other metabolites. In contrast, single and double knock-down plants displayed a few changes in their phenotype. A redundant function among the three M-sHSPs is indicated by the impairment in vegetative and reproductive growth associated with the simultaneous loss of all three M-sHSPs genes. The triple knock-down lines showed alteration of proteins mainly involved in photosynthesis and antioxidant defense compared to the control plants. On the other hand, heat stress triggered a distinct cytosolic response pattern and the upregulation of other sHSP members, in the knock-down plants. Overall, depletion of all three M-sHSPs in Arabidopsis severely impacted fundamental metabolic processes, leading to alterations in the correct plant growth and development. These findings expand our knowledge about the contribution of organelle-specific M-sHSPs to healthy plant growth under non-stress conditions.

Characterization of Two Small Heat Shock Protein Genes (Hsp17.4 and Hs20.3) from Sitodiplosis mosellana, and Their Expression Regulation during Diapause

Simple Summary

Small heat shock proteins (sHsps) play important roles in thermal adaptation of various organisms, and insect diapause. Sitodiplosis mosellana, a key pest of wheat worldwide, undergoes obligatory larval diapause in soil to survive adverse temperature extremes during hot summers and cold winters. The objectives of this study were to characterize two sHsp genes from S. mosellana (SmHsp17.4 and SmHsp20.3), and determine their expression in response to diapause, extreme high/low temperatures, or 20-hydroxyecdysone (20E) treatment. Expression of SmHsp17.4 was down-regulated upon entry into diapause, but up-regulated during the shift to post-diapause quiescence. In contrast, expression of SmHsp20.3 was not affected by entry into diapause, but was pronounced during summer and winter. Furthermore, transcripts of both SmHsps were highly responsive to heat (≥35 °C) and cold (≤−5 °C) during diapause, and topical application of 20E on diapausing larvae also induced SmHsp17.4 in a dose-dependent manner. Notably, the recombinant SmHsp17.4 and SmHsp20.3 exhibited significant molecular chaperone activity. In conclusion, SmHsp17.4 and SmHsp20.3 play essential roles in heat/cold adaptation, and 20E-mediated SmHsp17.4 was also likely involved in diapause termination. Results have improved our understanding of the molecular mechanism underlying diapause and related stress tolerance in S. mosellana.

Abstract

Sitodiplosis mosellana, a periodic but devastating wheat pest that escapes temperature extremes in summer and winter by undergoing obligatory diapause. To determine the roles of small heat shock proteins (sHsps) in diapause of S. mosellana, we characterized two sHsp genes, SmHsp17.4 and SmHsp20.3, from this species. Both SmHsps contained the conserved α-crystallin domain and the carboxy-terminal I/VXI/V motif of the sHsp family. SmHsp17.4 had one intron while SmHsp20.3 had none. Quantitative PCR revealed that SmHsp17.4 expression decreased after diapause initiation, but substantially increased during transition to post-diapause quiescence. In contrast, SmHsp20.3 expression was not affected by entry of diapause, but was clearly up-regulated during summer and winter. Short-term more severe heat-stress (≥35 °C) of over-summering larvae or cold-stress (≤−5 °C) of over-wintering larvae could stimulate higher expression of both genes, and SmHsp17.4 was more responsive to cold stress while SmHsp20.3 was more sensitive to heat stress. Notably, transcription of SmHsp17.4, but not SmHsp20.3, in diapausing larvae was inducible by 20-hydroxyecdysone (20E). Recombinant SmHsp17.4 and SmHsp20.3 proteins also displayed significant chaperone functionality. These findings suggest that both SmHsps play key roles in stress tolerance during diapause; and 20E-regulated SmHsp17.4 was also likely involved in diapause termination.

PiP2 favors an α-helical structure of non-recombinant Hsp12 of Saccharomyces cerevisiae

Hsp12 is a small heat shock protein of Saccharomyces cerevisiae upregulated in response to various stresses. Non recombinant Hsp12 has been purified and characterized. Using circular dichroism (CD), Isothermal Titration Calorimetry (ITC) and Differential Scanning Calorimetry (DSC), it has been demonstrated that the native Hsp12 is monomeric and intrinsically disordered (IDP). Hsp12 gains in structure in the presence of specific lipids (PiP₂). The helical form binds to liposomes models membrane with high affinity, leading to their rigidification. These results suggest that hydrophobic and ionic interactions are involved. Hsp12 is most likely a membrane chaperone expressed during stresses in Saccharomyces cerevisiae.

Heat shock proteins and the biogenesis of cellular membranes

The successful function of cells is importantly contributed by lipid membranes that are more than a simple physical barrier. The major components of cellular membranes are lipids, in particular glycerophospholipids, that have the capacity to assemble spontaneously into vesicles containing a lipid bilayer after exposure to an aqueous milieu due to their amphiphilic characteristics. The lipid capacity to form vesicles and encapsulate substrates has been proposed as a fundamental event during the biogenesis of cells. However, the stability of small vesicles is compromised during their expansion into larger and more complex particles. Recent observations by (Cornell et al. Proc Natl Acad Sci U S A 116:17239-17244, 2019) have shown that the insertion of amino acids into rudimentary vesicles could play a stabilizing role that was critical to the formation of early cells. Fatty acids were likely substituted by glycerophospholipids and amino acids replaced by polypeptides during the evolution of protocells. Thus, archaic peptides displaying lipid-binding and membrane-penetrating capacities could have played a key function in the development of current cells. In this regard, heat shock proteins (HSP), particularly the Hsp70 (HSPA) and small HSP (HSPB) families, could have portrayed that role. Indeed, bacterial DnaK is closest in sequence to the earliest members of the Hsp70 family and inserts into lipid membranes spontaneously. Moreover, extensive studies by the Vigh group have shown that, certainly, Hsp70s stabilize membranes. Thus, the ability of ancestral HSP70s and small HSPs to associate with lipids and stabilize membranes could have been a fundamental event in the genesis of cells.

Transcriptional Responses of the Heat Shock Protein 20 (Hsp20) and 40 (Hsp40) Genes to Temperature Stress and Alteration of Life Cycle Stages in the Harmful Alga Scrippsiella trochoidea (Dinophyceae)

Simple Summary

As the greatest contributors to harmful algal blooms, dinoflagellates account for roughly 75% of bloom events, which become an escalating threat to coastal ecosystems and cause substantial economic loss worldwide. Resting cyst production and broad temperature tolerance are well proven as adaptive strategies for blooming dinoflagellates; however, to date, the underlying molecular information is scarce. In the present study, we characterized two heat shock protein genes from the representative dinoflagellate Scrippsiella trochoidea, with the aim to primarily determine their possible roles in response to temperature stress and alteration of the life cycle. The yielded results enhance our knowledge about the functions of cross-talk of different Hsp members in temperature adaptation of dinoflagellates and facilitate further exploration in their potential physiological relevance during different life-stage alternation in this ecological important lineage.

Abstract

The small heat shock protein (sHsp) and Hsp40 are Hsp members that have not been intensively investigated but are functionally important in most organisms. In this study, the potential roles of a Hsp20 (StHsp20) and a Hsp40 (StHsp40) in dinoflagellates during adaptation to temperature fluctuation and alteration of different life stages were explored using the representative harmful algal blooms (HABs)-causative dinoflagellate species, Scrippsiella trochoidea. We isolated the full-length cDNAs of the two genes via rapid amplification of cDNA ends (RACE) and tracked their differential transcriptions via real-time qPCR. The results revealed StHsp20 and StHsp40 exhibited mRNA accumulation patterns that were highly similar in response to heat stress but completely different toward cold stress, which implies that the mechanisms underlying thermal and cold acclimation in dinoflagellates are regulated by different sets of genes. The StHsp20 was probably related to the heat tolerance of the species, and StHsp40 was closely involved in the adaptation to both higher and lower temperature fluctuations. Furthermore, significantly higher mRNA abundance of StHsp40 was detected in newly formed resting cysts, which might be a response to intrinsic stress stemmed from encystment. This finding also implied StHsp40 might be engaged in resting cyst formation of S. trochoidea. Our findings enriched the knowledge about possible cross-talk of different Hsp members in dinoflagellates and provided clues to further explore the molecular underpinnings underlying resting cyst production and broad temperature tolerance of this group of HABs contributors.

Interaction of alpha-crystallin with four major phospholipids of eye lens membranes

It is well-studied that the significant factor in cataract formation is the association of α-crystallin, a major eye lens protein, with the fiber cell plasma membrane of the eye lens. The fiber cell plasma membrane of the eye lens consists of four major phospholipids (PLs), i.e., phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylserine (PS), and sphingomyelin (SM). Despite several attempts to study the interaction of α-crystallin with PLs of the eye lens membrane, the role of individual PL for the binding with α-crystallin is still unclear. We recently developed the electron paramagnetic resonance (EPR) spin-labeling method to study the binding of α-crystallin to the PC membrane (Mainali et al., 2020a). Here, we use the recently developed EPR method to explicitly measure the binding affinity (K_a) of α-crystallin to the individual (PE*, PS, and SM) and two-component mixtures (SM/PE, SM/PS, and SM/PC in 70:30 and 50:50 mol%) of PL membranes as well as the physical properties (mobility parameter and maximum splitting) of these membranes upon binding with α-crystallin. One of the key findings of this study was that the K_a of α-crystallin binding to individual PL membranes followed the trends: K_a(PC) > K_a(SM) > K_a(PS) > K_a(PE*), indicating PE* inhibits binding the most whereas PC inhibits binding the least. Also, the K_a of α-crystallin binding to two-component mixtures of PL membranes followed the trends: K_a(SM/PE) > K_a(SM/PS) > K_a(SM/PC), indicating SM/PC inhibits binding the most whereas SM/PE inhibits binding the least. Except for the PE* membrane, for which there was no binding of α-crystallin, the mobility parameter for all other membranes decreased with an increase in α-crystallin concentration. It represents that the membranes become more immobilized near the headgroup regions of the PLs when more and more α-crystallin binds to them. The maximum splitting increased only for the SM and the SM/PE (70:30 mol%) membranes, with an increase in the binding of α-crystallin. It represents that the PL headgroup regions of these membranes become more ordered after binding of α-crystallin to these membranes. Our results showed that α-crystallin binds to PL membranes in a saturable manner. Also, our data suggest that the binding of α-crystallin to PL membranes likely occurs through hydrophobic interaction between α-crystallin and the hydrophobic fatty acid core of the membranes, and such interaction is modulated by the PL headgroup's size and charge, hydrogen bonding between headgroups, and PL curvature. Thus, this study provides an in-depth understanding of α-crystallin interaction with the PL membranes made of individual and two-component mixtures of the four major PLs of the eye lens membranes.

Multiple Functions of Spectrin: Convergent Effects

Spectrin is a multifunctional, multi-domain protein most well known in the membrane skeleton of mature human erythrocytes. Here we review the literature on the crosstalk of the chaperone activity of spectrin with its other functionalities. We hypothesize that the chaperone activity is derived from the surface exposed hydrophobic patches present in individual "spectrin-repeat" domains and show a competition between the membrane phospholipid binding functionality and chaperone activity of spectrin. Moreover, we show that post-translational modifications such as glycation which shield these surface exposed hydrophobic patches, reduce the chaperone function. On the other hand, oligomerization which is linked to increase of hydrophobicity is seen to increase it. We note that spectrin seems to prefer haemoglobin as its chaperone client, binding with it preferentially over other denatured proteins. Spectrin is also known to interact with unstable haemoglobin variants with a higher affinity than in the case of normal haemoglobin. We propose that chaperone activity of spectrin could be important in the cellular biochemistry of haemoglobin, particularly in the context of diseases.

Human HSPA9 (mtHsp70, mortalin) interacts with lipid bilayers containing cardiolipin, a major component of the inner mitochondrial membrane

Mitochondrial Hsp70 (HSPA9, mtHsp70, mortalin) in conjunction with a complex set of other proteins is involved in the transport of polypeptides across the mitochondrial matrix. This observation allows us to hypothesize that HSPA9 might interact with membranes directly, similarly to other Hsp70s. Thus, we investigated whether human HSPA9 could also get inserted into lipid membranes. Human HSPA9 was incubated with liposomes made of lipids found within the mitochondrial membrane, such as 1', 3'-bis [1, 2-dimyristoyl-sn-glycero-3-phospho]-glycerol (CL), palmitoyl-oleoyl phosphocholine (POPC), palmitoyl-oleoyl phosphoserine (POPS), and palmitoyl-oleoyl phosphoethanolamine (POPE). HSPA9 displayed a predilection for CL and POPS, and low affinity for POPC and POPE, suggesting that the proteins have high specificity for negatively charged phospholipids. Then, liposomes were made with a composition resembling either the outer or inner mitochondrial membrane (OMM or IMM, respectively). We observed that HSPA9 has a higher affinity for IMM than OMM, which is consistent with the higher content of CL in the IMM. A comparison for the incorporation into POPS or CL liposomes by HSPA9 or HSPA1 indicated that both proteins behaved very similarly when exposed to CL liposomes, but differently with POPS liposomes, which was further corroborated by their susceptibility to proteinase K digestion after incorporation into liposomes. The measurement of thermodynamic parameters also showed that the interaction of both proteins with CL and POPS liposomes was different. Overall, our data showed that HSPA9 is prone to interact with membranes resembling the IMM that may be important for its role in the translocation of proteins into the mitochondria.

Structural and functional properties of proteins interacting with small heat shock proteins

Small heat shock proteins (sHsps) are ubiquitous molecular chaperones found in all domains of life, possessing significant roles in protein quality control in cells and assisting the refolding of non-native proteins. They are efficient chaperones against many in vitro protein substrates. Nevertheless, the in vivo native substrates of sHsps are not known. To better understand the functions of sHsps and the mechanisms by which they enhance heat resistance, sHsp-interacting proteins were identified using affinity purification under heat shock conditions. This paper aims at providing some insights into the characteristics of natural substrate proteins of sHsps. It seems that sHsps of prokaryotes, as well as sHsps of some eukaryotes, can bind to a wide range of substrate proteins with a preference for certain functional classes of proteins. Using Drosophila melanogaster mitochondrial Hsp22 as a model system, we observed that this sHsp interacted with the members of ATP synthase machinery. Mechanistically, Hsp22 interacts with the multi-type substrate proteins under heat shock conditions as well as non-heat shock conditions.

Quantitative Profiling of Arabidopsis Polar Glycerolipids under Two Types of Heat Stress

At the cellular level, the remodelling of membrane lipids and production of heat shock proteins are the two main strategies whereby plants survive heat stress. Although many studies related to glycerolipids and HSPs under heat stress have been reported separately, detailed alterations of glycerolipids and the role of HSPs in the alterations of glycerolipids still need to be revealed. In this study, we profiled the glycerolipids of wild-type Arabidopsis and its HSP101-deficient mutant hot-1 under two types of heat stress. Our results demonstrated that the alterations of glycerolipids were very similar in wild-type Arabidopsis and hot-1 during heat stress. Although heat acclimation led to a slight decrease of glycerolipids, the decrease of glycerolipids in plants without heat acclimation is more severe under heat shock. The contents of 36:x monogalactosyl diacylglycerol (MGDG) were slightly increased, whereas that of 34:6 MGDG and 34:4 phosphatidylglycerol (PG) were severely decreased during moderate heat stress. Our findings suggested that heat acclimation could reduce the degradation of glycerolipids under heat shock. Synthesis of glycerolipids through the prokaryotic pathway was severely suppressed, whereas that through the eukaryotic pathway was slightly enhanced during moderate heat stress. In addition, HSP101 has a minor effect on the alterations of glycerolipids under heat stress.

Membrane-Associated Heat Shock Proteins in Oncology: From Basic Research to New Theranostic Targets

Heat shock proteins (HSPs) constitute a large family of conserved proteins acting as molecular chaperones that play a key role in intracellular protein homeostasis, regulation of apoptosis, and protection from various stress factors (including hypoxia, thermal stress, oxidative stress). Apart from their intracellular localization, members of different HSP families such as small HSPs, HSP40, HSP60, HSP70 and HSP90 have been found to be localized on the plasma membrane of malignantly transformed cells. In the current article, the role of membrane-associated molecular chaperones in normal and tumor cells is comprehensively reviewed with implications of these proteins as plausible targets for cancer therapy and diagnostics.

Modulation of Plasma Membrane Composition and Microdomain Organization Impairs Heat Shock Protein Expression in B16-F10 Mouse Melanoma Cells

The heat shock response (HSR) regulates induction of stress/heat shock proteins (HSPs) to preserve proteostasis during cellular stress. Earlier, our group established that the plasma membrane (PM) acts as a sensor and regulator of HSR through changes in its microdomain organization. PM microdomains such as lipid rafts, dynamic nanoscale assemblies enriched in cholesterol and sphingomyelin, and caveolae, cholesterol-rich PM invaginations, constitute clustering platforms for proteins functional in signaling cascades. Here, we aimed to compare the effect of cyclodextrin (MβCD)- and nystatin-induced cholesterol modulations on stress-activated expression of the representative HSPs, HSP70, and HSP25 in mouse B16-F10 melanoma cells. Depletion of cholesterol levels with MβCD impaired the heat-inducibility of both HSP70 and HSP25. Sequestration of cholesterol with nystatin impaired the heat-inducibility of HSP25 but not of HSP70. Imaging fluorescent correlation spectroscopy marked a modulated lateral diffusion constant of fluorescently labelled cholesterol in PM during cholesterol deprived conditions. Lipidomics analysis upon MβCD treatment revealed, next to cholesterol reductions, decreased lysophosphatidylcholine and phosphatidic acid levels. These data not only highlight the involvement of PM integrity in HSR but also suggest that altered dynamics of specific cholesterol pools could represent a mechanism to fine tune HSP expression.

Imaging FCS delineates subtle heterogeneity in plasma membranes of resting mast cells

A myriad of transient, nanoscopic lipid- and protein-based interactions confer a steady-state organization of the plasma membrane in resting cells that is poised to orchestrate assembly of key signaling components upon reception of an extracellular stimulus. Although difficult to observe directly in live cells, these subtle interactions can be discerned by their impact on the diffusion of membrane constituents. Here, we quantified the diffusion properties of a panel of structurally distinct lipid, lipid-anchored, and transmembrane (TM) probes in RBL mast cells by imaging fluorescence correlation spectroscopy (ImFCS). We developed a statistical analysis of data combined from many pixels over multiple cells to characterize differences in diffusion coefficients as small as 10%, which reflect differences in underlying interactions. We found that the distinctive diffusion properties of lipid probes can be explained by their dynamic partitioning into Lo-like proteolipid nanodomains, which encompass a major fraction of the membrane and whose physical properties are influenced by actin polymerization. Effects on diffusion of functional protein modules in both lipid-­anchored and TM probes reflect additional complexity in steady state membrane organization. The contrast we observe between different probes diffusing through the same membrane milieu represents the dynamic resting steady state, which serves as a baseline for monitoring plasma membrane remodeling that occurs upon stimulation.

The small heat shock proteins, HSPB1 and HSPB5, interact differently with lipid membranes

Increasing evidence shows that heat shock proteins (hsp) escape the cytosol gaining access to the extracellular environment, acting as signaling agents. Since the majority of these proteins lack the information necessary for their export via the classical secretory pathway, attention has been focused on alternative releasing mechanisms. Crossing the plasma membrane is a major obstacle to the secretion of a cytosolic protein into the extracellular milieu. Several mechanisms have been proposed, including direct interaction with the plasma membrane or their release within extracellular vesicles (ECV). HSPB1 (Hsp27), which belongs to the small hsp family, was detected within the membrane of ECV released from stressed HepG2 cells. To further investigate this finding, we studied the interaction of HSPB1 with lipid membranes using liposomes. We found that HSPB1 interacted with liposomes made of palmitoyl oleoyl phosphatidylserine (POPS), palmitoyl oleoyl phosphatidylcholine (POPC), and palmitoyl oleoyl phosphatidylglycerol (POPG), with different characteristics. Another member of the small hsp family, HSPB5 (αB-crystallin), has also been detected within ECV released from HeLa cells transfected with this gene. This protein was found to interact with liposomes as well, but differently than HSPB1. To address the regions interacting with the membrane, proteoliposomes were digested with proteinase K and the protected domains within the liposomes were identified by mass spectroscopy. We observed that large parts of HSPB1 and HSPB5 were embedded within the liposomes, particularly the alpha-crystallin domain. These observations suggest that the interaction with lipid membranes may be part of the mechanisms of export of these proteins.

Chaperone potential of erythroid spectrin: Effects of hemoglobin interaction, macromolecular crowders, phosphorylation and glycation

Spectrin, the major protein component of the erythrocyte membrane skeleton has chaperone like activity and is known to bind membrane phospholipids and hemoglobin. We have probed the chaperone activity of spectrin in presence of hemoglobin and phospholipid SUVs of different compositions to elucidate the effect of phospholipid/hemoglobin binding on chaperone function. It is seen that spectrin displays a preference for hemoglobin over other substrates leading to a decrease in chaperone activity in presence of hemoglobin. A competition is seen to exist between phospholipid binding and chaperone function of spectrin, in a dose dependent manner with the greatest extent of decrease being seen in case of phospholipid vesicles containing aminophospholipids e.g. PS and PE which may have implications in diseases like hereditary spherocytosis where mutation in spectrin is implicated in its detachment from cell membrane. To gain a clearer understanding of the chaperone like activity of spectrin under in-vivo like conditions we have investigated the effect of macromolecular crowders as well as phosphorylation and glycation states on chaperone activity. It is seen that the presence of non-specific, protein and non-protein macromolecular crowders do not appreciably affect chaperone function. Phosphorylation also does not affect the chaperone function unlike glycation which progressively diminishes chaperone activity. We propose a model where chaperone clients adsorb onto spectrin's surface and processes that bind to and occlude these surfaces decrease chaperone activity.

Characterization of genes encoding small heat shock proteins from Bemisia tabaci and expression under thermal stress

Small heat shock proteins (sHSPs) are probably the most diverse in structure and function among the various super-families of stress proteins, and they play essential roles in various biological processes. The sweet potato whitefly, Bemisia tabaci (Gennadius), feeds in the phloem, transmits several plant viruses, and is an important pest on cotton, vegetables and ornamentals. In this research, we isolated and characterized three α-crystallin/sHSP family genes (Bthsp19.5, Bthsp19.2, and Bthsp21.3) from Bemisia tabaci. The three cDNAs encoded proteins of 171, 169, and 189 amino acids with calculated molecular weights of 19.5, 19.2, and 21.3 kDa and isoelectric points of 6.1, 6.2, and 6.0, respectively. The deduced amino acid sequences of the three genes showed strong similarity to sHSPs identified in Hemiptera and Thysanoptera insects species. All three sHSPs genes from Bemisia tabaci lacked introns. Quantitative real-time PCR analyses revealed that the three BtsHSPs genes were significantly up-regulated in Bemisia tabaci adults and pupae during high temperature stress (39, 41, 43, and 45 °C) but not in response to cold temperature stress (-6, -8, -10, and -12 °C). The expression levels of Bthsp19.2 and Bthsp21.3 in pupae was higher than adults in response to heat stress, while the expression level of Bthsp19.5 in adults was higher than pupae. In conclusion, this research results show that the sHSP genes of Bemisia tabaci had shown differential expression changes under thermal stress.

Identification and Expression Analysis of Four Small Heat Shock Protein Genes in Cigarette Beetle, Lasioderma serricorne (Fabricius)

Small heat shock proteins (sHsps) are molecular chaperones that play crucial roles in the stress adaption of insects. In this study, we identified and characterized four sHsp genes (LsHsp19.4, 20.2, 20.3, and 22.2) from the cigarette beetle, Lasioderma serricorne (Fabricius). The four cDNAs encoded proteins of 169, 180, 181, and 194 amino acids with molecular weights of 19.4, 20.2, 20.3, and 22.2 kDa, respectively. The four LsHsp sequences possessed a typical sHsp domain structure. Quantitative real-time PCR analyses revealed that LsHsp19.4 and 20.3 transcripts were most abundant in pupae, whereas the transcript levels of LsHsp20.2 and 22.2 were highest in adults. Transcripts of three LsHsp genes were highly expressed in the larval fat body, whereas LsHsp20.2 displayed an extremely high expression level in the gut. Expression of the four LsHsp genes was dramatically upregulated in larvae exposed to 20-hydroxyecdysone. The majority of the LsHsp genes were significantly upregulated in response to heat and cold treatments, while LsHsp19.4 was insensitive to cold stress. The four genes were upregulated when challenged by immune triggers (peptidoglycan isolated from Staphylococcus aureus and from Escherichia coli 0111:B4). Exposure to CO₂ increased LsHsp20.2 and 20.3 transcript levels, but the LsHsp19.4 transcript level declined. The results suggest that different LsHsp genes play important and distinct regulatory roles in L. serricorne development and in response to diverse stresses.

Review: Adaptation of Beneficial Propionibacteria, Lactobacilli, and Bifidobacteria Improves Tolerance Toward Technological and Digestive Stresses

This review deals with beneficial bacteria, with a focus on lactobacilli, propionibacteria, and bifidobacteria. As being recognized as beneficial bacteria, they are consumed as probiotics in various food products. Some may also be used as starters in food fermentation. In either case, these bacteria may be exposed to various environmental stresses during industrial production steps, including drying and storage, and during the digestion process. In accordance with their adaptation to harsh environmental conditions, they possess adaptation mechanisms, which can be induced by pretreatments. Adaptive mechanisms include accumulation of compatible solutes and of energy storage compounds, which can be largely modulated by the culture conditions. They also include the regulation of energy production pathways, as well as the modulation of the cell envelop, i.e., membrane, cell wall, surface layers, and exopolysaccharides. They finally lead to the overexpression of molecular chaperones and of stress-responsive proteases. Triggering these adaptive mechanisms can improve the resistance of beneficial bacteria toward technological and digestive stresses. This opens new perspectives for the improvement of industrial processes efficiency with regard to the survival of beneficial bacteria. However, this bibliographical survey evidenced that adaptive responses are strain-dependent, so that growth and adaptation should be optimized case-by-case.