Cryoprotective mechanism of a small intrinsically disordered dehydrin protein

Unravelling the involvement of protein disorder in cyanobacterial stress responses

This study has explored the involvement of Intrinsically Disordered Proteins (IDPs) in cyanobacterial stress response. IDPs possess distinct physicochemical properties, which allow them to execute diverse functions. Anabaena PCC 7120, the model photosynthetic, nitrogen-fixing cyanobacterium encodes 688 proteins (11 % of the total proteome) with at least one intrinsically disordered region (IDR). Of these, 130 proteins that showed >30 % overall disorder were designated as IDPs. Physico-chemical analysis, showed these IDPs to adopt shapes ranging from 'globular' to 'tadpole-like'. Upon exposure to NaCl, 41 IDP-encoding genes were found to be differentially expressed. Surprisingly, most of these were induced, indicating the importance of IDP-accumulation in overcoming salt stress. Subsequently, six IDPs were identified to be induced by multiple stresses (salt, ammonium and selenite). Interestingly, the presence of these 6-multiple stress-induced IDPs was conserved in filamentous cyanobacteria. Utilizing the experimental proteomic data of Anabaena, these 6 IDPs were found to interact with many proteins involved in diverse pathways, underscoring their physiological importance as protein hubs. This study lays the framework for IDP-related research in Anabaena by (a) identifying, as well as physiochemically characterizing, all the disordered proteins and (b) uncovering a subset of IDPs that are likely to be critical in adaptation to environmental stresses.

Prokaryotic expression, purification, and the in vitro and in vivo protection study of dehydrin WDHN2 from Triticum aestivum

Dehydrins proteins accumulate and play important protective roles in most plants during abiotic stresses. The objective of this study was to characterize a YSK2-type dehydrin gene, WDHN2, isolated from Triticum aestivum previously. In this work, wheat dehydrin WDHN2 was expressed in Escherichia coli and purified by immobilized metal affinity chromatography, which exhibited as a single band by sodium dodecyl sulfonate polyacrylamide gel electrophoresis and western blotting. We show that WDHN2 is capable of alleviating lactate dehydrogenase inactivation from heat and desiccation in vitro enzyme activity protection assay. In vivo assay of Escherichia coli viability demonstrates the enhancement of cell survival by the overexpression of WDHN2. The protein aggregation prevention assay explores that WDHN2 has a broad protective effect on the cellular proteome. The results show that WDHN2 is mainly accumulated in the nucleus and cytosol, suggesting that this dehydrin may exert its function in both cellular compartments. Our data suggest that WDHN2 acts as a chaperone molecular in vivo.

Plant dehydrins and dehydrin-like proteins: characterization and participation in abiotic stress response

Abiotic stress has a significant impact on plant growth and development. It causes changes in the subcellular organelles, which, due to their stress sensitivity, can be affected. Cellular components involved in the abiotic stress response include dehydrins, widely distributed proteins forming a class II of late embryogenesis abundant protein family with characteristic properties including the presence of evolutionarily conserved sequence motifs (including lysine-rich K-segment, N-terminal Y-segment, and often phosphorylated S motif) and high hydrophilicity and disordered structure in the unbound state. Selected dehydrins and few poorly characterized dehydrin-like proteins participate in cellular stress acclimation and are also shown to interact with organelles. Through their functioning in stabilizing biological membranes and binding reactive oxygen species, dehydrins and dehydrin-like proteins contribute to the protection of fragile organellar structures under adverse conditions. Our review characterizes the participation of plant dehydrins and dehydrin-like proteins (including some organellar proteins) in plant acclimation to diverse abiotic stress conditions and summarizes recent updates on their structure (the identification of dehydrin less conserved motifs), classification (new proposed subclasses), tissue- and developmentally specific accumulation, and key cellular activities (including organellar protection under stress acclimation). Recent findings on the subcellular localization (with emphasis on the mitochondria and plastids) and prospective applications of dehydrins and dehydrin-like proteins in functional studies to alleviate the harmful stress consequences by means of plant genetic engineering and a genome editing strategy are also discussed.

Isolation and molecular characterization of an FSK2-type dehydrin from Atriplex halimus

Dehydrins form the group II LEA protein family and are known to play multiple roles in plant stress tolerance and enzyme protection. They harbor a variable number of conserved lysine rich motifs (K-segments) and may also contain three additional conserved motifs (Y-, F- and S-segments). In this work, we report the isolation and characterization of an FSK₂-type dehydrin from the halophytic species Atriplex halimus, which we designate as AhDHN1. In silico analysis of the protein sequence revealed that AhDHN1 contains large number of hydrophilic residues, and is predicted to be intrinsically disordered. In addition, it has an FSK₂ architecture with one F-segment, one S-segment, and two K-segments. The expression analysis showed that the AhDHN1 transcript is induced by salt and water stress treatments in the leaves of Atriplex seedlings. Moreover, circular dichroism spectrum performed on recombinant AhDHN1 showed that the dehydrin lacks any secondary structure, confirming its intrinsic disorder nature. However, there is a gain of α-helicity in the presence of membrane-like SDS micelles. In vitro assays revealed that AhDHN1 is able to effectively protect enzymatic activity of the lactate dehydrogenase against cold, heat and dehydration stresses. Our findings strongly suggest that AhDHN1 can be involved in the adaptation mechanisms of halophytes to adverse environments.

The cationic nature of lysine-rich segments modulates the structural and biochemical properties of wild potato FSK3 dehydrin

Dehydrins are hydrophilic stress-induced proteins that are thought to protect cellular machinery from the adverse effect of dehydration caused by low temperature, drought, or salinity. In the previous study, acidic FSK₃ dehydrin DHN24 from Solanum sogarandinum was found to accumulate at multiple sites in phloem cells in response to cold treatment. This study investigated the biochemical and structural properties of recombinant DHN24. It was shown that the overexpression of DHN24 in Escherichia coli led to the inhibition of bacterial growth. The purified DHN24 was found to protect lactate dehydrogenase from freeze-induced denaturation. Circular dichroism (CD) analysis showed that DHN24 was disordered in aqueous solutions, but adopted α-helical conformation in a membrane-mimetic environment using sodium dodecyl sulfate micelles. DHN24 also interacted with anionic phosphatidic acid (PA). DHN24 contains four lysine-rich regions including three K-segments and a region upstream of the S-segment. The role of their local cationic nature is unknown. These segments are predicted to form helical structures. The CD analysis of mutant proteins in the membrane-mimetic environment matched these predictions most closely, revealing that the positively charged lysine residues in these regions promoted disorder-to-order transitions. Moreover, the inhibition of bacterial growth and interactions with PA were regulated by the local cationic nature of DHN24, while no such regulation was observed for its cryoprotective activity. The importance of the positive charge of the lysine-rich segments and disordered structure for DHN24 activity is discussed in relation to its possible biological function.

The Effect of Positive Charge Distribution on the Cryoprotective Activity of Dehydrins

Dehydrins are intrinsically disordered proteins expressed ubiquitously throughout the plant kingdom in response to desiccation. Dehydrins have been found to have a cryoprotective effect on lactate dehydrogenase (LDH) in vitro, which is in large part influenced by their hydrodynamic radius rather than the order of the amino acids within the sequence (alternatively, this may be a sequence specific effect). However, it seems that a different mechanism may underpin the cryoprotection that they confer to the cold-labile yeast frataxin homolog-1 (Yfh1). Circular dichroism spectroscopy (CD) was used to assess the degree of helicity of Yfh1 at 1 °C, both alone and in the presence of several dehydrin constructs. Three constructs were compared to the wild type: YSK₂-K→R (lysine residues substituted with arginine), YSK₂-Neutral (locally neutralized charge), and YSK₂-SpaceK (evenly distributed positive charge). The results show that sequence rearrangements and minor substitutions have little impact on the ability of the dehydrin to preserve LDH activity. However, when the positive charge of the dehydrin is locally neutralized or evenly distributed, the dehydrin becomes less efficient at promoting structure in Yfh1 at low temperatures. This suggests that a stabilizing, charge-based interaction occurs between dehydrins and Yfh1. Dehydrins are intrinsically disordered proteins, expressed by certain organisms to improve desiccation tolerance. These proteins are thought to serve many cellular roles, such as the stabilization of membranes, DNA, and proteins. However, the molecular mechanisms underlying the function of dehydrins are not well understood. Here, we examine the importance of positive charges in dehydrin sequences by making substitutions and comparing their effects in the cryoprotection of two different proteins.

Evaluation of a bacterial group 1 LEA protein as an enzyme protectant from stress-induced inactivation

Late embryogenesis abundant (LEA) proteins are hydrophilic proteins that lack a well-ordered tertiary structure and accumulate to high levels in response to water deficit, in organisms such as plants, fungi, and bacteria. The mechanisms proposed to protect cellular structures and enzymes are water replacement, ion sequestering, and membrane stabilization. The activity of some proteins has a limited shelf-life due to instability that can be caused by their structure or the presence of a stress condition that limits their activity; several LEA proteins have been shown to behave as cryoprotectants in vitro. Here, we report a group1 LEA from Azotobacter vinelandii AvLEA1, capable of conferring protection to lactate dehydrogenase, catechol dioxygenase, and Baylase peroxidase against freeze-thaw treatments, desiccation, and oxidative damage, making AvLEA a promising biological stabilizer reagent. This is the first evidence of protection provided by this LEA on enzymes with biotechnological potential, such as dioxygenase and peroxidase under in vitro stress conditions. Our results suggest that AvLEA could act as a molecular chaperone, or a "molecular shield," preventing either dissociation or antiaggregation, or as a radical scavenger, thus preventing damage to these target enzymes during induced stress. KEY POINTS: • This work expands the basic knowledge of the less-known bacterial LEA proteins and their in vitro protection potential. • AvLEA is a bacterial protein that confers in vitro protection to three enzymes with different characteristics and oligomeric arrangement. • The use of AvLEA as a stabilizer agent could be further explored using dioxygenase and peroxidase in bioremediation treatments. AvLEA1 protects against freeze-thaw treatments, desiccation, and oxidative damage on three different enzymes with biotechnological potential.

Investigating the Functional Role of the Cysteine Residue in Dehydrin from the Arctic Mouse-Ear Chickweed Cerastium arcticum

The stress-responsive, SK₅ subclass, dehydrin gene, CaDHN, has been identified from the Arctic mouse-ear chickweed Cerastium arcticum. CaDHN contains an unusual single cysteine residue (Cys143), which can form intermolecular disulfide bonds. Mutational analysis and a redox experiment confirmed that the dimerization of CaDHN was the result of an intermolecular disulfide bond between the cysteine residues. The biochemical and physiological functions of the mutant C143A were also investigated by in vitro and in vivo assays using yeast cells, where it enhanced the scavenging of reactive oxygen species (ROS) by neutralizing hydrogen peroxide. Our results show that the cysteine residue in CaDHN helps to enhance C. arcticum tolerance to abiotic stress by regulating the dimerization of the intrinsically disordered CaDHN protein, which acts as a defense mechanism against extreme polar environments.

Expression, Purification, and Preliminary Protection Study of Dehydrin PicW1 From the Biomass of Picea wilsonii

Dehydrins (DHNs) belong to group II of late embryogenesis-abundant (LEA) proteins, which are up-regulated in most plants during cold, drought, heat, or salinity stress. Despite the importance of dehydrins for the plants to resist abiotic stresses, it is necessary to obtain plant-derived dehydrins from different biomass. Generally, dehydrin PicW1 from Picea wilsonii is involved in Kn-type dehydrin with five K-segments, which has a variety of biological activities. In this work, Picea wilsonii dehydrin PicW1 was expressed in Escherichia coli and purified by chitin-affinity chromatography and size-exclusion chromatography, which showed as a single band by SDS-PAGE. A cold-sensitive enzyme of lactate dehydrogenase (LDH) is used to explore the protective activities of other proteins. Temperature stress assays showed that PicW1 had an effective protective effect on LDH activity, which was better than that of bovine serum albumin (BSA). This study provides insights into the purification and protective activity of K5 DHNs for the advancement of dehydrin structure and function from biomass.

Physiological, Structural, and Functional Insights Into the Cryoprotection of Membranes by the Dehydrins

Plants can be exposed to cold temperatures and have therefore evolved several mechanisms to prevent damage caused by freezing. One of the most important targets are membranes, which are particularly susceptible to cold damage. To protect against such abiotic stresses, plants express a family of proteins known as late embryogenesis abundant (LEA) proteins. Many LEA proteins are intrinsically disordered, that is, they do not contain stable secondary or tertiary structures alone in solution. These proteins have been shown in a number of studies to protect plants from damage caused by cold, drought, salinity, and osmotic stress. In this family, the most studied proteins are the type II LEA proteins, better known as dehydrins (dehydration-induced proteins). Many physiological studies have shown that dehydrins are often located near the membrane during abiotic stress and that the expression of dehydrins helps to prevent the formation of oxidation-modified lipids and reduce the amount of electrolyte leakage, two hallmarks of damaged membranes. One of the earliest biophysical clues that dehydrins are involved in membrane cryoprotection came from in vitro studies that demonstrated a binding interaction between the protein and membranes. Subsequent work has shown that one conserved motif, known as K-segments, is involved in binding, while recent studies have used NMR to explore the residue specific structure of dehydrins when bound to membranes. The biophysical techniques also provide insight into the mechanism by which dehydrins protect the membrane from cold stress, which appears to mainly involve the lowering of the transition temperature.

The Halophyte Dehydrin Sequence Landscape

Dehydrins (DHNs) belong to the LEA (late embryogenesis abundant) family group II, that comprise four conserved motifs (the Y-, S-, F-, and K-segments) and are known to play a multifunctional role in plant stress tolerance. Based on the presence and order of these segments, dehydrins are divided into six subclasses: YnSKn, FnSKn, YnKn, SKn, Kn, and KnS. DHNs are rarely studied in halophytes, and their contribution to the mechanisms developed by these plants to survive in extreme conditions remains unknown. In this work, we carried out multiple genomic analyses of the conservation of halophytic DHN sequences to discover new segments, and examine their architectures, while comparing them with their orthologs in glycophytic plants. We performed an in silico analysis on 86 DHN sequences from 10 halophytic genomes. The phylogenetic tree showed that there are different distributions of the architectures among the different species, and that FSKn is the only architecture present in every plant studied. It was found that K-, F-, Y-, and S-segments are highly conserved in halophytes and glycophytes with a few modifications, mainly involving charged amino acids. Finally, expression data collected for three halophytic species (Puccinillia tenuiflora, Eutrema salsugenium, and Hordeum marinum) revealed that many DHNs are upregulated by salt stress, and the intensity of this upregulation depends on the DHN architecture.

The Disordered Dehydrin and Its Role in Plant Protection: A Biochemical Perspective

Dehydrins are intrinsically disordered proteins composed of several well conserved sequence motifs known as the Y-, S-, F-, and K-segments, the latter of which is a defining feature of all dehydrins. These segments are interspersed by regions of low sequence conservation and are organized modularly, which results in seven different architectures: Kn, SKn, YnSKn, YnKn, KnS, FnK and FnSKn. Dehydrins are expressed ubiquitously throughout the plant kingdom during periods of low intracellular water content, and are capable of improving desiccation tolerance in plants. In vitro evidence of dehydrins shows that they are involved in the protection of membranes, proteins and DNA from abiotic stresses. However, the molecular mechanisms by which these actions are achieved are as of yet somewhat unclear. With regards to macromolecule cryoprotection, there is evidence to suggest that a molecular shield-like protective effect is primarily influenced by the hydrodynamic radius of the dehydrin and to a lesser extent by the charge and hydrophobicity. The interaction between dehydrins and membranes is thought to be a surface-level, charge-based interaction that may help to lower the transition temperature, allowing membranes to maintain fluidity at low temperatures and preventing membrane fusion. In addition, dehydrins are able to protect DNA from damage, showing that these abiotic stress protection proteins have multiple roles.

Salt stress proteins in plants: An overview

Salinity stress is considered the most devastating abiotic stress for crop productivity. Accumulating different types of soluble proteins has evolved as a vital strategy that plays a central regulatory role in the growth and development of plants subjected to salt stress. In the last two decades, efforts have been undertaken to critically examine the genome structure and functions of the transcriptome in plants subjected to salinity stress. Although genomics and transcriptomics studies indicate physiological and biochemical alterations in plants, it do not reflect changes in the amount and type of proteins corresponding to gene expression at the transcriptome level. In addition, proteins are a more reliable determinant of salt tolerance than simple gene expression as they play major roles in shaping physiological traits in salt-tolerant phenotypes. However, little information is available on salt stress-responsive proteins and their possible modes of action in conferring salinity stress tolerance. In addition, a complete proteome profile under normal or stress conditions has not been established yet for any model plant species. Similarly, a complete set of low abundant and key stress regulatory proteins in plants has not been identified. Furthermore, insufficient information on post-translational modifications in salt stress regulatory proteins is available. Therefore, in recent past, studies focused on exploring changes in protein expression under salt stress, which will complement genomic, transcriptomic, and physiological studies in understanding mechanism of salt tolerance in plants. This review focused on recent studies on proteome profiling in plants subjected to salinity stress, and provide synthesis of updated literature about how salinity regulates various salt stress proteins involved in the plant salt tolerance mechanism. This review also highlights the recent reports on regulation of salt stress proteins using transgenic approaches with enhanced salt stress tolerance in crops.

Cryoprotective activities of FK20, a human genome-derived intrinsically disordered peptide against cryosensitive enzymes without a stereospecific molecular interaction

Background

Intrinsically disordered proteins (IDPs) have been shown to exhibit cryoprotective activity toward other cellular enzymes without any obvious conserved sequence motifs. This study investigated relationships between the physical properties of several human genome-derived IDPs and their cryoprotective activities.

Methods

Cryoprotective activity of three human-genome derived IDPs and their truncated peptides toward lactate dehydrogenase (LDH) and glutathione S-transferase (GST) was examined. After the shortest cryoprotective peptide was defined (named FK20), cryoprotective activity of all-D-enantiomeric isoform of FK20 (FK20-D) as well as a racemic mixture of FK20 and FK20-D was examined. In order to examine the lack of increase of thermal stability of the target enzyme, the CD spectra of GST and LDH in the presence of a racemic mixture of FK20 and FK20-D at varying temperatures were measured and used to estimate Tm.

Results

Cryoprotective activity of IDPs longer than 20 amino acids was nearly independent of the amino acid length. The shortest IDP-derived 20 amino acid length peptide with sufficient cryoprotective activity was developed from a series of TNFRSF11B fragments (named FK20). FK20, FK20-D, and an equimolar mixture of FK20 and FK20-D also showed similar cryoprotective activity toward LDH and GST. Tm of GST in the presence and absence of an equimolar mixture of FK20 and FK20-D are similar, suggesting that IDPs’ cryoprotection mechanism seems partly from a molecular shielding effect rather than a direct interaction with the target enzymes.

Evolutionary analysis of angiosperm dehydrin gene family reveals three orthologues groups associated to specific protein domains

Dehydrins (DHNs) are a family of plant proteins that play important roles on abiotic stress tolerance and seed development. They are classified into five structural subgroups: K-, SK-, YK-, YSK-, and KS-DHNs, according to the presence of conserved motifs named K-, Y- and S- segments. We carried out a comparative structural and phylogenetic analysis of these proteins, focusing on the less-studied KS-type DHNs. A search for conserved motifs in DHNs from 56 plant genomes revealed that KS-DHNs possess a unique and highly conserved N-terminal, 15-residue amino acid motif, not previously described. This novel motif, that we named H-segment, is present in DHNs of angiosperms, gymnosperms and lycophytes, suggesting that HKS-DHNs were present in the first vascular plants. Phylogenetic and microsynteny analyses indicate that the five structural subgroups of angiosperm DHNs can be assigned to three groups of orthologue genes, characterized by the presence of the H-, F- or Y- segments. Importantly, the hydrophilin character of DHNs correlate with the phylogenetic origin of the DHNs rather than to the traditional structural subgroups. We propose that angiosperm DHNs can be ultimately subdivided into three orthologous groups, a phylogenetic framework that should help future studies on the evolution and function of this protein family.

Plant Group II LEA Proteins: Intrinsically Disordered Structure for Multiple Functions in Response to Environmental Stresses

In response to various environmental stresses, plants have evolved a wide range of defense mechanisms, resulting in the overexpression of a series of stress-responsive genes. Among them, there is certain set of genes that encode for intrinsically disordered proteins (IDPs) that repair and protect the plants from damage caused by environmental stresses. Group II LEA (late embryogenesis abundant) proteins compose the most abundant and characterized group of IDPs; they accumulate in the late stages of seed development and are expressed in response to dehydration, salinity, low temperature, or abscisic acid (ABA) treatment. The physiological and biochemical characterization of group II LEA proteins has been carried out in a number of investigations because of their vital roles in protecting the integrity of biomolecules by preventing the crystallization of cellular components prior to multiple stresses. This review describes the distribution, structural architecture, and genomic diversification of group II LEA proteins, with some recent investigations on their regulation and molecular expression under various abiotic stresses. Novel aspects of group II LEA proteins in Phoenix dactylifera and in orthodox seeds are also presented. Genome-wide association studies (GWAS) indicated a ubiquitous distribution and expression of group II LEA genes in different plant cells. In vitro experimental evidence from biochemical assays has suggested that group II LEA proteins perform heterogenous functions in response to extreme stresses. Various investigations have indicated the participation of group II LEA proteins in the plant stress tolerance mechanism, spotlighting the molecular aspects of group II LEA genes and their potential role in biotechnological strategies to increase plants' survival in adverse environments.

Dehydrin MsDHN1 improves aluminum tolerance of alfalfa (Medicago sativa L.) by affecting oxalate exudation from root tips

A SK3 -type dehydrin MsDHN1 was cloned from alfalfa (Medicago sativa L.). Its function and gene regulatory pathways were studied via overexpression and suppression of MsDHN1 in alfalfa seedlings or hairy roots. The results showed that MsDHN1 is a typical intrinsically disordered protein that exists in the form of monomers and homodimers in alfalfa. The plant growth rates increased as a result of MsDHN1 overexpression (MsDHN1-OE) and decreased upon MsDHN1 suppression (MsDHN1-RNAi) in seedlings or hairy roots of alfalfa compared with the wild-type or the vector line under Al stress. MsDHN1 interacting with aquaporin (AQP) MsPIP2;1 and MsTIP1;1 positively affected oxalate secretion from root tips and Al accumulation in root tips. MsABF2 was proven to be an upstream transcription factor of MsDHN1 and activated MsDHN1 expression by binding to the ABRE element of the MsDHN1 promoter. The transcriptional regulation of MsABF2 on MsDHN1 was dependent on the abscisic acid signaling pathway. These results indicate that MsDHN1 can increase alfalfa tolerance to Al stress via increasing oxalate secretion from root tips, which may involve in the interaction of MsDHN1 with two AQP.

An intrinsically disordered radish vacuolar calcium-binding protein (RVCaB) showed cryoprotective activity for lactate dehydrogenase with its hydrophobic region

A soluble protein fraction from radish (Raphanus sativus L.) taproot had cryoprotective activity for lactate dehydrogenase (LDH). The activity was found mainly in the heat-stable fractions of soluble proteins. The cryoprotective protein, whose molecular mass was 43 kDa in sodium dodecyl sulfate polyacrylamide gel electrophoresis, was obtained by successive chromatographies on TOYOPEARL SuperQ and TOYOPEARL DEAE. MALDI-TOF MS/MS analysis indicated that the purified protein was a radish vacuolar calcium-binding protein (RVCaB), which is reportedly related to calcium storage in the vacuoles of radish taproot. The purified RVCaB inhibited the cryoinactivation, cryodenaturation, and cryoaggregation of LDH. RVCaB had greater cryoprotective activity than general cryoprotectants. When RVCaB was divided into 15 segments (Seg01 to Seg15, 15 amino acids each), Seg03, which had a high hydrophobicity scale, showed remarkable cryoprotective activity. This indicated that RVCaB protected LDH from freezing and thawing damage presumably through a specific hydrophobic area (i.e., Seg03).

The in vitro structure and functions of the disordered late embryogenesis abundant three proteins

Late embryogenesis abundant (LEA) proteins are produced during seed embryogenesis and in vegetative tissue in response to various abiotic stressors. A correlation has been established between LEA expression and stress tolerance, yet their precise biochemical mechanism remains elusive. LEA proteins are very rich in hydrophilic amino acids, and they have been found to be intrinsically disordered proteins (IDPs) in vitro. Here, we perform biochemical and structural analyses of the four LEA3 proteins from Arabidopsis thaliana (AtLEA3). We show that the LEA3 proteins are disordered in solution but have regions with propensity for order. All LEA3 proteins were effective cryoprotectants of LDH in the freeze/thaw assays, while only one member, AtLEA3-4, was shown to bind Cu²⁺ and Fe³⁺ ions with micromolar affinity. As well, only AtLEA3-4 showed binding and a gain in α-helicity in the presence of the membrane mimic dodecylphosphocholine (DPC). We explored this interaction in greater detail using ¹⁵ N-heteronuclear single quantum coherence (HSQC) nuclear magnetic resonance, and demonstrate that two sets of conserved motifs present in AtLEA3-4 are involved in the interaction with the DPC micelles, which themselves gain α-helical structure.

Functional characterization of VviDHN2 and VviDHN4 dehydrin isoforms from Vitis vinifera (L.): An in silico and in vitro approach

Dehydrins, a family of hydrophilic and intrinsically disordered proteins, are a subgroup of late embryogenesis abundant proteins that perform different protective roles in plants. Although the transition from a disordered to an ordered state has been associated with dehydrin function or interactions with specific partner molecules, the question of how the primary and secondary dehydrin protein structure is related to specific functions or target molecule preferences remains unresolved. This work addresses the in silico sequencing analysis and in vitro functional characterization of two dehydrin isoforms, VviDHN2 and VviDHN4, from Vitis vinifera. Conformational changes suggest potential interactions with a broad range of molecules and could point to more than one function. The in silico analysis showed differences in conserved segments, specific amino acid binding sequences, heterogeneity of structural properties and predicted sites accessible for various post-translational modifications between the sequence of both dehydrins. Moreover, in vitro functional analysis revealed that although they both showed slight antifungal activity, only VviDHN4 acts as a molecular shield that protects proteins from freezing and dehydration. VviDHN4 also demonstrated high potential as a chaperone and reactive oxygen species scavenger, in addition to presenting antifreeze activity, all of which confirms its multifunctional nature. Our findings highlight the significant role of Y-segments and the differential and specific amino acid composition of less conserved segments that are rich in polar/charged residues between S- and K-segments, coupled with post-translational modifications, in modulating and switching dehydrin biological function.

Cryoprotective activity of Arabidopsis KS-type dehydrin depends on the hydrophobic amino acids of two active segments

Dehydrins are intrinsically disordered proteins which are related to cold tolerance in plants. Dehydrins show potent cryoprotective activities for freeze-sensitive enzymes such as lactate dehydrogenase (LDH). Previous studies demonstrated that K-segments conserved in dehydrins had cryoprotective activities and that K-segment activities depended on the hydrophobic amino acids in the segment. However, the cryoprotective roles of hydrophobic amino acids in dehydrin itself have not been reported. Here, we demonstrated that hydrophobic amino acids were required for the cryoprotective activity of Arabidopsis dehydrin AtHIRD11. Cryoprotective activities were compared between AtHIRD11 and the corresponding mutant in which all hydrophobic residues were changed to T (AtHIRD11Φ/T) by using LDH. The change strikingly reduced AtHIRD11 activity. A segmentation analysis indicated that the conserved K-segment (Kseg) and a previously unidentified segment (non-K-segment 1, NK1) showed cryoprotective activities. Circular dichroism indicated that the secondary structures of all peptides showed disorder, but only cryoprotective peptides changed to the ordered forms by sodium dodecyl sulfate. Ultracentrifuge analysis indicated that AtHIRD11 and AtHIRD11Φ/T had similar molecular sizes in solution. These results suggest that not only structural disorder but also hydrophobic amino acids contributed to the cryoprotective activity of AtHIRD11. A possible mechanism based on an extended molecular shield model is proposed.

Presence of intrinsically disordered proteins can inhibit the nucleation phase of amyloid fibril formation of Aβ(1-42) in amino acid sequence independent manner

The molecular shield effect was studied for intrinsically disordered proteins (IDPs) that do not adopt compact and stable protein folds. IDPs are found among many stress-responsive gene products and cryoprotective- and drought-protective proteins. We recently reported that some fragments of human genome-derived IDPs are cryoprotective for cellular enzymes, despite a lack of relevant amino acid sequence motifs. This sequence-independent IDP function may reflect their molecular shield effect. This study examined the inhibitory activity of IDPs against fibril formation in an amyloid beta peptide (Aβ(1–42)) model system. Four of five human genome-derived IDPs (size range 20 to 44 amino acids) showed concentration-dependent inhibition of amyloid formation (IC₅₀ range between 60 and 130 μM against 20 μM Aβ(1–42)). The IC₅₀ value was two orders of magnitude lower than that of polyethylene-glycol and dextran, used as neutral hydrophilic polymer controls. Nuclear magnetic resonance with ¹⁵ N-labeled Aβ(1–42) revealed no relevant molecular interactions between Aβ(1–42) and IDPs. The inhibitory activities were abolished by adding external amyloid-formation seeds. Therefore, IDPs seemed to act only at the amyloid nucleation phase but not at the elongation phase. These results suggest that IDPs (0.1 mM or less) have a molecular shield effect that prevents aggregation of susceptible molecules.

F-segments of Arabidopsis dehydrins show cryoprotective activities for lactate dehydrogenase depending on the hydrophobic residues

Although dehydrins show cryoprotective activities for freeze-sensitive enzymes, the underlying mechanism is still under investigation. Here, we report that F-segments conserved in some dehydrins cryoprotected lactate dehydrogenase (LDH) as well as K-segments, which were previously identified as cryoprotective segments of dehydrins. The cryoprotective activity levels of four F-segments of Arabidopsis dehydrins were similar to that of a typical K-segment. Amino acid substitution experiments indicated that the activity of the F-segment of Arabidopsis COR47 (designated as Fseg) depended on the hydrophobic residues (L, F, and V). Intriguingly, when all the amino acids other than the hydrophobic residues were changed to glycine, the cryoprotective activity did not change, suggesting that the hydrophobic amino acids were sufficient for Fseg activity. Circular dichroism analysis indicated that Fseg was mainly disordered in aqueous solution as well as Fseg_Φ/T, in which the hydrophobic residues of Fseg were changed to T. This suggested that the hydrophobic interaction might be related to the cryoprotective activities of Fseg.

Protective functions of alternative splicing transcripts (CdDHN4-L and CdDHN4-S) of CdDHN4 from bermudagrass under multiple abiotic stresses

Dehydrins (DHNs) play critical roles in plant adaptation to abiotic stresses. The objective of this study was to characterize DHNs in bermudagrass (Cynodon spp.). CdDHN4 gene was cloned from bermudagrass ‘Tifway’. Two CdDHN4 transcripts were detected due to alternative splicing (the nonspliced CdDHN4-L and the spliced CdDHN4-S) and both the CdDHN4-S and CdDHN4-L proteins are YSK₂-type DHNs, the Φ-segment is present in CdDHN4-L and absent in CdDHN4-S. Transgenic Arabidopsis thaliana expressing CdDHN4-L or CdDHN4-S exhibited improved tolerance to salt, osmotic, low temperature and drought stress compared to the wild type (WT). The two transgenic lines did not differ in salt or drought tolerance, while plants expressing CdDHN4-S grew better under osmotic stress than those expressing CdDHN4-L. Both transgenic lines exhibited reduced content of malondialdehyde (MDA) and reactive oxygen species (ROS); and higher antioxidant enzymatic activities than the wild type plants under salt or drought stress. CdDHN4-S exhibited a higher ROS-scavenging capacity than CdDHN4-L.

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Two CdDHN4 transcripts (CdDHN4-L and CdDHN4-S) were detected due to alternative splicing in bermudagrass ‘Tifway’.

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CdDHN4s transgenic Arabidopsis thaliana exhibited higher tolerance to multiple abiotic stress compared to the wild type.

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CdDHN4s transgenic lines has lower content of ROS than the wild type under salt or drought stress.

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CdDHN4-S had a higher ROS-scavenging capacity than CdDHN4-L.

Lysine, Lysine-Rich, Serine, and Serine-Rich Proteins: Link Between Metabolism, Development, and Abiotic Stress Tolerance and the Role of ncRNAs in Their Regulation

Lysine (Lys) is indispensable nutritionally, and its levels in plants are modulated by both transcriptional and post-transcriptional control during plant ontogeny. Animal glutamate receptor homologs have been detected in plants, which may participate in several plant processes through the Lys catabolic products. Interestingly, a connection between Lys and serotonin metabolism has been established recently in rice. 2-Aminoadipate, a catabolic product of Lys appears to play a critical role between serotonin accumulation and the color of rice endosperm/grain. It has also been shown that expression of some lysine-methylated proteins and genes encoding lysine-methyltransferases (KMTs) are regulated by cadmium even as it is known that Lys biosynthesis and its degradation are modulated by novel mechanisms. Three complex pathways co-exist in plants for serine (Ser) biosynthesis, and the relative preponderance of each pathway in relation to plant development or abiotic stress tolerance are being unfolded slowly. But the phosphorylated pathway of L-Ser biosynthesis (PPSB) appears to play critical roles and is essential in plant metabolism and development. Ser, which participates indirectly in purine and pyrimidine biosynthesis and plays a pivotal role in plant metabolism and signaling. Also, L-Ser has been implicated in plant responses to both biotic and abiotic stresses. A large body of information implicates Lys-rich and serine/arginine-rich (SR) proteins in a very wide array of abiotic stresses. Interestingly, a link exists between Lys-rich K-segment and stress tolerance levels. It is of interest to note that abiotic stresses largely influence the expression patterns of SR proteins and also the alternative splicing (AS) patterns. We have checked if any lncRNAs form a cohort of differentially expressed genes from the publicly available PPSB, sequence read archives of NCBI GenBank. Finally, we discuss the link between Lys and Ser synthesis, catabolism, Lys-proteins, and SR proteins during plant development and their myriad roles in response to abiotic stresses.

Dehydrin ERD14 activates glutathione transferase Phi9 in Arabidopsis thaliana under osmotic stress

BACKGROUND

Fully intrinsically disordered plant dehydrin ERD14 can protect enzymes via its chaperone-like activity, but it was not formally linked with enzymes of the plant redox system yet. This is of particular interest, as the level of H₂O₂ in Arabidopsis plants increases during osmotic stress, which can be counteracted by overexpression of ERD14.

METHODS

The proteomic mass-spectrometry analysis of stressed plants was performed to find the candidates affected by ERD14. With cross-linking, microscale thermophoresis, and active-site titration kinetics, the interaction and influence of ERD14 on the function of two target proteins: glutathione transferase Phi9 and catalase was examined.

RESULTS

Under osmotic stress, redox enzymes, specifically the glutathione transferase Phi enzymes, are upregulated. Using microscale thermophoresis, we showed that ERD14 directly interacts with GSTF9 with a K_D of ~25 μM. ERD14 activates the inactive GSTF9 molecules, protects GSTF9 from oxidation, and can also increases the activity of the enzyme. Aside from GSTF9, we found that ERD14 can also interact with catalase, an important cellular H₂O₂ scavenging enzyme, with a K_D of ~0.13 μM, and protects it from dehydration-induced loss of activity.

CONCLUSIONS

We propose that fully intrinsically disordered dehydrin ERD14 might protect and even activate redox enzymes, helping plants to survive oxidative stress under dehydration conditions.

GENERAL SIGNIFICANCE

ERD14 has a direct effect on the activity of redox enzymes.

Binding of a Vitis riparia dehydrin to DNA

Plants must protect themselves from abiotic stresses such as drought, cold, and high salinity. The common thread of all three stresses is that they cause dehydration, which in turn promotes the formation of reactive oxygen species (ROS). Dehydrin proteins (dehydrins) are a large family of proteins that have been identified in nearly all land plants, and whose presence is correlated with plant protection from abiotic stresses. Several dehydrin studies have shown that some dehydrins localize to the nucleus, as well as the cytoplasm, but a functional role for nuclear dehydrins has not yet been determined. We show here that the Vitis riparia dehydrin VrDHN1 localizes to the nucleus and is able to bind to DNA to protect it from damage caused by hydrogen peroxide, an ROS source. We also show that the binding to DNA is not DNA-sequence specific, suggesting that the protein is able to protect any exposed DNA without interfering with its normal function. NMR studies show that the binding is largely driven by the lysine-rich nature of dehydrins located in the conserved K-segments. Unlike other, previously studied dehydrins, VrDHN1 binding to DNA is not enhanced through the presence of metals. Lastly, we demonstrate that the Y-segment does not bind ATP, as has long been proposed.

Protecting Enzymes from Stress-Induced Inactivation

The pharmaceutical and chemical industries depend on additives to protect enzymes and other proteins against stresses that accompany their manufacture, transport, and storage. Common stresses include vacuum-drying, freeze-thawing, and freeze-drying. The additives include sugars, compatible osmolytes, amino acids, synthetic polymers, and both globular and disordered proteins. Scores of studies have been published on protection, but the data have never been analyzed systematically. To spur efforts to understand the sources of protection and ultimately develop more effective formulations, we review ideas about the mechanisms of protection, survey the literature searching for patterns of protection, and then compare the ideas to the data.

Y2SK2 and SK3 type dehydrins from Agapanthus praecox can improve plant stress tolerance and act as multifunctional protectants

Two dehydrins from Agapanthus praecox (ApY₂SK₂ and ApSK₃) show important protective effects under complex stresses. Both ApY₂SK₂ and ApSK₃ contain one intron and consist of a full-length cDNA of 981 bp and 1057 bp encoding 186 and 215 amino acids, respectively. ApY₂SK₂ and ApSK₃ transgenic Arabidopsis thaliana show reduced plasma membrane damage and ROS levels and higher antioxidant activity and photosynthesis capability under salt, osmotic, cold and drought stresses compared with the wild-type. ApY₂SK₂ and ApSK₃ are mainly located in the cytoplasm and cell membrane, and ApY₂SK₂ can even localize in the nucleus. In vitro tests indicate that ApY₂SK₂ and ApSK₃ can effectively protect enzyme activity during the freeze-thaw process, and ApY₂SK₂ also exhibits this function during desiccation treatment. Furthermore, ApY₂SK₂ and ApSK₃ can significantly inhibit hydroxyl radical generation. These two dehydrins can bind metal ions with a binding affinity of Co²⁺> Ni²⁺> Cu²⁺> Fe³⁺; the binding affinity of ApSK₃ is higher than that of ApY₂SK₂. Thus, ApY₂SK₂ has a better protective effect on enzyme activity, and ApSK₃ has stronger metal ion binding function and effect on ROS metabolism. Moreover, plant cryopreservation evaluation tests indicate that ApY₂SK₂ and ApSK₃ transformation can enhance the seedling survival ratio from 23% to 47% and 55%, respectively; the addition of recombinant ApY₂SK₂ and ApSK₃ to plant vitrification solution may increase the survival ratio of wild-type A. thaliana seedlings from 24% to 50% and 46%, respectively. These findings suggest that ApY₂SK₂ and ApSK₃ can effectively improve cell stress tolerance and have great potential for in vivo or in vitro applications.

Sequence composition versus sequence order in the cryoprotective function of an intrinsically disordered stress-response protein

Intrinsically disordered stress proteins have been shown to act as chaperones, protecting proteins from damage caused by stresses such as freezing and thawing. Dehydration proteins (dehydrins) are intrinsically disordered stress proteins that are found in almost all land plants. They consist of a variable number of the short, semi-conserved, Y-, S-, and K-segments, with longer stretches of poorly conserved sequences in between. Previous studies have provided conflicting views on the details of the dehydrin cryoprotective mechanism of enzymes. Experiments with polyethylene glycol (PEG) have shown that PEG cryoprotective efficiency is the same as dehydrins of the same hydrodynamic radius, suggesting that the protein's disordered and polar nature is important, rather than the specific order of the residues. To further elucidate the mechanism, we created scrambled variants of the wild grape dehydrins K₂ and YSK₂ and tested their ability to protect lactate dehydrogenase and yeast frataxin homolog-1 from freeze/thaw damage. The results show that for preventing aggregation, it is the sequence composition and the size of the dehydrin that is the most important factor in protection, while for freeze/thaw damage causing loss of secondary structure, it is the sequence composition that is most significant.

Protecting activity of desiccated enzymes

Protein-based biological drugs and many industrial enzymes are unstable, making them prohibitively expensive. Some can be stabilized by formulation with excipients, but most still require low temperature storage. In search of new, more robust excipients, we turned to the tardigrade, a microscopic animal that synthesizes cytosolic abundant heat soluble (CAHS) proteins to protect its cellular components during desiccation. We find that CAHS proteins protect the test enzymes lactate dehydrogenase and lipoprotein lipase against desiccation-, freezing-, and lyophilization-induced deactivation. Our data also show that a variety of globular and disordered protein controls, with no known link to desiccation tolerance, protect our test enzymes. Protection of lactate dehydrogenase correlates, albeit imperfectly, with the charge density of the protein additive, suggesting an approach to tune protection by modifying charge. Our results support the potential use of CAHS proteins as stabilizing excipients in formulations and suggest that other proteins may have similar potential.

Evolution of the modular, disordered stress proteins known as dehydrins

Dehydrins, plant proteins that are upregulated during dehydration stress conditions, have modular sequences that can contain three conserved motifs (the Y-, S-, and K-segments). The presence and order of these motifs are used to classify dehydrins into one of five architectures: Kn, SKn, KnS, YnKn, and YnSKn, where the subscript n describes the number of copies of that motif. In this study, an architectural and phylogenetic analysis was performed on 426 dehydrin sequences that were identified in 53 angiosperm and 3 gymnosperm genomes. It was found that angiosperms contained all five architectures, while gymnosperms only contained Kn and SKn dehydrins. This suggests that the ancestral dehydrin in spermatophytes was either Kn or SKn, and the Y-segment containing dehydrins first arose in angiosperms. A high-level split between the YnSKn dehydrins from either the Kn or SKn dehydrins could not be confidently identified, however, two lower level architectural divisions appear to have occurred after different duplication events. The first likely occurred after a whole genome duplication, resulting in the duplication of a Y3SK2 dehydrin; the duplicate subsequently lost an S- and K- segment to become a Y3K1 dehydrin. The second split occurred after a tandem duplication of a Y1SK2 dehydrin, where the duplicate lost both the Y- and S- segment and gained four K-segments, resulting in a K6 dehydrin. We suggest that the newly arisen Y3K1 dehydrin is possibly on its way to pseudogenization, while the newly arisen K6 dehydrin developed a novel function in cold protection.

Evidence for in vivo interactions between dehydrins and the aquaporin AtPIP2B

Plants have developed mechanisms that allow them to tolerate different abiotic stresses. Among these mechanisms, the accumulation of specific proteins such as dehydrins (DHNs) and aquaporins (AQPs) can protect other proteins from damage during dehydration and may allow the control of water loss, respectively. Although both types of proteins are involved in plant protection against dehydration stress, a direct interaction between them has not been explored. A previous screen to identify potential OpsDHN1 protein interactions revealed an aquaporin as a possible candidate. Here, we used the Bimolecular Fluorescence Complementation (BiFC) approach to investigate the direct interaction of the cactus OpsDHN1 protein with the Arabidopsis plasma membrane PIP family aquaporin AtPIP2B (At2G37170). Since AtPIP2B is a membrane protein and OpsDHN1 is a cytosolic protein that may be peripherally associated with membranes, we propose that OpsDHN1/AtPIP2B interaction takes place at cellular membranes. Furthermore, we also demonstrate the interaction of AtPIP2B with the three Arabidopsis dehydrins COR47 (AT1G20440), ERD10 (At1g20450), and RAB18 (At5g66400).

Characterization of Dehydrin protein, CdDHN4-L and CdDHN4-S, and their differential protective roles against abiotic stress in vitro

BACKGROUND

Dehydrins play positive roles in regulating plant abiotic stress responses. The objective of this study was to characterize two dehydrin genes, CdDHN4-L and CdDHN4-S, generated by alternative splicing of CdDHN4 in bermudagrass.

RESULTS

Overexpression of CdDHN4-L with φ-segment and CdDHN4-S lacking of φ-segment in Arabidopsis significantly increased tolerance against abiotic stresses. The growth phenotype of Arabidopsis exposed to NaCl at 100 mM was better in plants overexpressing CdDHN4-L than those overexpressing CdDHN4-S, as well as better in E.coli cells overexpressing CdDHN4-L than those overexpressing CdDHN4-S in 300 and 400 mM NaCl, and under extreme temperature conditions at - 20 °C and 50 °C. The CdDHN4-L had higher disordered characterization on structures than CdDHN4-S at temperatures from 10 to 90 °C. The recovery activities of lactic dehydrogenase (LDH) and alcohol dehydrogenase (ADH) in presence of CdDHN4-L and CdDHN4-S were higher than that of LDH and ADH alone under freeze-thaw damage and heat. Protein-binding and bimolecular fluorescence complementation showed that both proteins could bind to proteins with positive isoelectric point via electrostatic forces.

CONCLUSIONS

These results indicate that CdDHN4-L has higher protective ability against abiotic stresses due to its higher flexible unfolded structure and thermostability in comparison with CdDHN4-S. These provided direct evidence of the function of the φ-segment in dehydrins for protecting plants against abiotic stress and to show the electrostatic interaction between dehydrins and client proteins.

Structural and Functional Dynamics of Dehydrins: A Plant Protector Protein under Abiotic Stress

Abiotic stress affects the growth and development of crops tremendously, worldwide. To avoid adverse environmental effects, plants have evolved various efficient mechanisms to respond and adapt to harsh environmental factors. Stress conditions are associated with coordinated changes in gene expressions at a transcriptional level. Dehydrins have been extensively studied as protectors in plant cells, owing to their vital roles in sustaining the integrity of membranes and lactate dehydrogenase (LDH). Dehydrins are highly hydrophilic and thermostable intrinsically disordered proteins (IDPs), with at least one Lys-rich K-segment. Many dehydrins are induced by multiple stress factors, such as drought, salt, extreme temperatures, etc. This article reviews the role of dehydrins under abiotic stress, regulatory networks of dehydrin genes, and the physiological functions of dehydrins. Advances in our understanding of dehydrin structures, gene regulation and their close relationships with abiotic stresses demonstrates their remarkable ability to enhance stress tolerance in plants.

Effect of an Intrinsically Disordered Plant Stress Protein on the Properties of Water

Dehydrins are plant proteins that are able to protect plants from various forms of dehydrative stress such as drought, cold, and high salinity. Dehydrins can prevent enzymes from losing activity after freeze/thaw treatments. Previous studies had suggested that the dehydrins function by a molecular shield effect, essentially preventing a denatured enzyme from aggregating with another enzyme. Therefore, the larger the dehydrin, the larger the shield and theoretically the more effective the protection. Although this relationship holds for smaller dehydrins, it fails to explain why larger dehydrins are less efficient than would be predicted from their size. Using solvatochromic dyes to probe the solvent features of water, we first confirm that the dehydrins do not bind the dyes, which would interfere with interpretation of the data. We then show that the dehydrins have an effect on three solvent properties of water (dipolarity/polarizability, hydrogen-bond donor acidity and hydrogen-bond acceptor basicity), which can contribute to the protective mechanism of these proteins. Interpretation of these data suggests that although polyethylene glycol and dehydrins have similar protective effects, dehydrins may more efficiently modify the hydrogen-bonding ability of bulk water to prevent enzyme denaturation. This possibly explains why dehydrins recover slightly more enzyme activity than polyethylene glycol.

Does water stress promote the proteome-wide adjustment of intrinsically disordered proteins in plants?

Plant response to water stress involves the activation of mechanisms expected to help them cope with water scarcity. Among these mechanisms, proteome-wide adjustment is well known. This includes actions to save energy, protect cellular and molecular components, and maintain vital functions of the cell. Intrinsically disordered proteins, which are proteins without a rigid three-dimensional structure, are seen as emerging multifunctional cellular components of proteomes. They are highly abundant in eukaryotic proteomes, and numerous functions for these proteins have been proposed. Here, we discuss several reasons why the collection of intrinsically disordered proteins in a proteome (disordome) could be subjected to an active regulation during conditions of water scarcity in plants. We also discuss the potential misinterpretations of disordome content estimations made so far due to bias-prone data and the need for reliable analysis based on experimental data in order to acknowledge the plasticity nature of the disordome.

Discovery of Cryoprotective Activity in Human Genome-Derived Intrinsically Disordered Proteins

Intrinsically disordered proteins (IDPs) are an emerging phenomenon. They may have a high degree of flexibility in their polypeptide chains, which lack a stable 3D structure. Although several biological functions of IDPs have been proposed, their general function is not known. The only finding related to their function is the genetically conserved YSK₂ motif present in plant dehydrins. These proteins were shown to be IDPs with the YSK₂ motif serving as a core region for the dehydrins’ cryoprotective activity. Here we examined the cryoprotective activity of randomly selected IDPs toward the model enzyme lactate dehydrogenase (LDH). All five IDPs that were examined were in the range of 35–45 amino acid residues in length and were equally potent at a concentration of 50 μg/mL, whereas folded proteins, the PSD-95/Dlg/ZO-1 (PDZ) domain, and lysozymes had no potency. We further examined their cryoprotective activity toward glutathione S-transferase as an example of the other enzyme, and toward enhanced green fluorescent protein as a non-enzyme protein example. We further examined the lyophilization protective activity of the peptides toward LDH, which revealed that some IDPs showed a higher activity than that of bovine serum albumin (BSA). Based on these observations, we propose that cryoprotection is a general feature of IDPs. Our findings may become a clue to various industrial applications of IDPs in the future.

In vivo evidence for homo- and heterodimeric interactions of Arabidopsis thaliana dehydrins AtCOR47, AtERD10, and AtRAB18

Dehydrins (DHNs) are intrinsically disordered proteins that play central roles in plant abiotic stress responses; however, how they work remains unclear. Herein, we report the in planta subcellular localization of Arabidopsis thaliana DHNs AtCOR47, AtERD10, and AtRAB18 through GFP translational fusions. To explore the dimerization ability of the Arabidopsis acidic DHNs AtCOR47 and AtERD10, we conducted an in planta DHN binding assay using the Bimolecular Fluorescence Complementation (BiFC) technique. Our analyses revealed homodimeric interactions for AtCOR47 and AtERD10; interestingly, heterodimeric associations also occurred with these DHNs, and these interactions were observed in the cytosol of tobacco cells. Furthermore, we evaluated whether Arabidopsis basic DHNs, such as AtRAB18, could also interact with itself and/or with AtCOR47 and AtERD10 in the BiFC system. Our data revealed homodimeric RAB18 complexes in the nucleus and cytosol, while heterodimeric associations between AtRAB18 and acidic DHNs occurred only in the cytosol. Finally, we demonstrated the presence of heterodimeric complexes among Arabidopsis AtCOR47, AtERD10, and AtRAB18 DHNs with their acidic ortholog the OpsDHN1 from Opuntia streptacantha; these heterodimeric interactions showed different subcellular distributions. Our results guide DHN research toward a new scenario where DHN/DHN oligomerization could be explored as a part of their molecular mechanism.

Structure of an Intrinsically Disordered Stress Protein Alone and Bound to a Membrane Surface

Dehydrins are a group of intrinsically disordered proteins that protect plants from damage caused by drought, cold, and high salinity. Like other intrinsically disordered proteins, dehydrins can gain structure when bound to a ligand. Previous studies have shown that dehydrins are able to protect liposomes from cold damage, but the interactions that drive membrane binding and the detailed structure of the bound and unbound forms are not known. We use an ensemble-structure approach to generate models of a dehydrin known as K2 in the presence and absence of sodium dodecyl sulfate micelles, and we docked the bound structure to the micelle. The collection of residual dipolar coupling data, amide protection factors, and paramagnetic relaxation enhancement distances, in combination with chemical shifts and relaxation measurements, allows for determining plausible structures that are not otherwise visible in time-averaged structural data. The results show that in the bound structure, the conserved lysines are important for membrane binding, whereas the flanking hydrophobic residues play a lesser role. The unbound structure shows a high level of disorder and an extended structure. We propose that the structural differences between bound and unbound forms allow dehydrins to act as molecular shields in their unbound state and as membrane protectants in their bound state. Unlike α-synuclein, the significant gain of α-helicity in K2 at low concentrations of sodium dodecyl sulfate is not due to a decrease in the critical micelle concentration. The study provides structural insight into how a disordered protein can interact with a membrane surface.

The role of hydrophobic amino acids of K-segments in the cryoprotection of lactate dehydrogenase by dehydrins

Dehydrins, which are group 2 late embryogenesis abundant (LEA) proteins, accumulate in plants during the development of the embryo and exposure to abiotic stresses including low temperature. Dehydrins exhibit cryoprotection of freezing-sensitive enzymes, e.g. lactate dehydrogenase (LDH). Although it has been reported that K-segments conserved in dehydrins are related to their cryoprotection activity, it has not been determined which sequence features of the K-segments contribute to the cryoprotection. A cryoprotection assay using LDH indicated that 13 K-segments including 12 K-segments found in Arabidopsis dehydrins and a typical K-segment (TypK, EKKGIMEKIKEKLPG) derived from the K-segments of many plants showed similar cryoprotective activities. Mutation of the TypK sequence demonstrated that hydrophobic amino acids were clearly involved in preventing the cryoinactivation, cryoaggregation, and cryodenaturation of LDH. We propose that the cryoprotective activities of dehydrins may be made possible by the hydrophobic residues of the K-segments.

CRISPR-induced null alleles show that Frost protects Drosophila melanogaster reproduction after cold exposure

The ability to survive and reproduce after cold exposure is important in all kingdoms of life. However, even in a sophisticated genetic model system like Drosophila melanogaster, few genes have been identified as functioning in cold tolerance. The accumulation of the Frost (Fst) gene transcript increases after cold exposure, making it a good candidate for a gene that has a role in cold tolerance. However, despite extensive RNAi knockdown analysis, no role in cold tolerance has been assigned to Fst. CRISPR is an effective technique for completely knocking down genes, and less likely to produce off-target effects than GAL4-UAS RNAi systems. We have used CRISPR-mediated homologous recombination to generate Fst null alleles, and these Fst alleles uncovered a requirement for FST protein in maintaining female fecundity following cold exposure. However, FST does not have a direct role in survival following cold exposure. FST mRNA accumulates in the Malpighian tubules, and the FST protein is a highly disordered protein with a putative signal peptide for export from the cell. Future work is needed to determine whether FST is exported from the Malpighian tubules and directly interacts with female reproductive tissues post-cold exposure, or if it is required for other repair/recovery functions that indirectly alter energy allocation to reproduction.

Different dehydrins perform separate functions in Physcomitrella patens

Dehydrins, PpDHNA and PpDHNB from Physcomitrella patens provide drought and cold tolerance while PpDHNC shows antimicrobial property suggesting different dehydrins perform separate functions in P. patens. The moss Physcomitrella patens can withstand extremes of environmental condition including abiotic stress such as dehydration, salinity, low temperature and biotic stress such as pathogen attack. Osmotic stress is inflicted under both cold and drought stress conditions where dehydrins have been found to play a significant protective role. In this study, a comparative analysis was drawn for the three dehydrins PpDHNA, PpDHNB and PpDHNC from P. patens. Our data shows that PpDHNA and PpDHNB play a major role in cellular protection during osmotic stress. PpDHNB showed several fold upregulation of the gene when P. patens was subjected to cold and osmotic stress in combination. PpDHNA and PpDHNB provide protection to enzyme lactate dehydrogenase under osmotic as well as freezing conditions. PpDHNC possesses antibacterial activity and thus may have a role in biotic stress response. Overexpression of PpDHNA, PpDHNB and PpDHNC in transgenic tobacco showed a better performance for PpDHNB with respect to cold and osmotic stress. These results suggest that specific dehydrins contribute to tolerance of mosses under different stress conditions.

YSK2 Type Dehydrin (SbDhn1) from Sorghum bicolor Showed Improved Protection under High Temperature and Osmotic Stress Condition

YSK2 type dehydrin from Sorghum bicolor (SbDhn1) showed a high level of transcript accumulation when subjected to high temperature and osmotic stress. The high transcript level occurring in such stress situation might lead to a protective effect; though the exact mechanism by which this is achieved remains poorly understood. Nevertheless, our results provide compelling evidence to prove that transgenic tobacco lines overexpressing SbDhn1 gene showed improve stress tolerance as assessed by reduced membrane damage and low MDA content. Furthermore, we demonstrate here SbDhn1 expressing lines were only able to recover after stress treatment. In this study, we have provided direct evidence for the protection rendered by SbDHN1 protein to a temperature-sensitive enzyme under both high temperature and osmotic stress. We extended this analysis to the whole plant proteome where the addition of SbDHN1 protein helped in retaining the solubility of the protein was demonstrated. Interestingly, in vitro experiments carried out with lactate dehydrogenase (LDH), showed aggregate formation upon subjecting it to high temperature. However, in presence of SbDHN1 protein very few aggregates were observed. Aggregation assay showed a high level of aggregates in wild-type or empty vector transformed plants as compared to SbDhn1 transgenic lines. Confocal microscopy images in leaf peel sections of wild-type plants showed high amounts of aggregates as compared with transgenic lines. This study provides evidence for the protection rendered by SbDHN1 protein under high temperature by inhibiting the aggregate formation and provide the rational for the mechanism how these proteins ameliorate the adverse stress conditions.

Genome Analysis of Conserved Dehydrin Motifs in Vascular Plants

Dehydrins, a large family of abiotic stress proteins, are defined by the presence of a mostly conserved motif known as the K-segment, and may also contain two other conserved motifs known as the Y-segment and S-segment. Using the dehydrin literature, we developed a sequence motif definition of the K-segment, which we used to create a large dataset of dehydrin sequences by searching the Pfam00257 dehydrin dataset and the Phytozome 10 sequences of vascular plants. A comprehensive analysis of these sequences reveals that lysine residues are highly conserved in the K-segment, while the amino acid type is often conserved at other positions. Despite the Y-segment name, the central tyrosine is somewhat conserved, but can be substituted with two other small aromatic amino acids (phenylalanine or histidine). The S-segment contains a series of serine residues, but in some proteins is also preceded by a conserved LHR sequence. In many dehydrins containing all three of these motifs the S-segment is linked to the K-segment by a GXGGRRKK motif (where X can be any amino acid), suggesting a functional linkage between these two motifs. An analysis of the sequences shows that the dehydrin architecture and several biochemical properties (isoelectric point, molecular mass, and hydrophobicity score) are dependent on each other, and that some dehydrin architectures are overexpressed during certain abiotic stress, suggesting that they may be optimized for a specific abiotic stress while others are involved in all forms of dehydration stress (drought, cold, and salinity).

Isolation, cloning, and characterization of a novel Sorghum dehydrin (SbDhn2) protein

Plants can produce their own set of defense molecules in an attempt to survive under stressed conditions. Dehydrins play a considerable role in protecting the plants under varied stress situations. We have isolated a novel SK3 type dehydrin from Sorghum capable of protecting the enzyme lactate dehydrogenase in vitro under both cold and high temperature. This protein showed non-canonical migration in a sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) due to the high hydrophilicity of the protein. The high percentage of glycine and histidine residues present in the protein sequence is responsible for the radical scavenging activity of the protein. The protein also exhibited binding affinity to metal ions owing to the histidine-rich motifs, therefore chelating the metal ions and making them unavailable to systems responsible for generation of reactive oxygen species (ROS). In the presence of specific metal ions, the protein showed reversible aggregation with certain degree of protease resistivity along with induction of secondary structures. The resistivity of the protein to degradation might be implicated in stress situations, thus leading to an increase in the shelf life of the protein. Association with metal ions like copper and zinc at a fairly low concentration increased the protective effect of the SbDHN2 protein for lactate dehydrogenase (LDH) activity to a considerable extent. The synthesis of this dehydrin in stressed plants might help the plant in rendering stress tolerance.