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Cellular stress results in the release of damage-associated molecular pattern (DAMP) molecules that promote inflammatory responses. Here Ping Wang and colleagues show that cold-inducible RNA-binding protein (CIRP) is a DAMP that is released into the circulation in response to hemorrhagic shock and sepsis. It promotes proinflammatory cytokine release by binding to the TLR4-MD2 complex. Blockade of CIRP reduces inflammation, organ injury and mortality in animal models of hemorrhage and sepsis, suggesting that CIRP may be targeted therapeutically in these conditions. A systemic inflammatory response is observed in patients undergoing hemorrhagic shock and sepsis. Here we report increased levels of cold-inducible RNA-binding protein (CIRP) in the blood of individuals admitted to the surgical intensive care unit with hemorrhagic shock. In animal models of hemorrhage and sepsis, CIRP is upregulated in the heart and liver and released into the circulation. In macrophages under hypoxic stress, CIRP translocates from the nucleus to the cytosol and is released. Recombinant CIRP stimulates the release of tumor necrosis factor-α (TNF-α) and HMGB1 from macrophages and induces inflammatory responses and causes tissue injury when injected in vivo . Hemorrhage-induced TNF-α and HMGB1 release and lethality were reduced in CIRP-deficient mice. Blockade of CIRP using antisera to CIRP attenuated inflammatory cytokine release and mortality after hemorrhage and sepsis. The activity of extracellular CIRP is mediated through the Toll-like receptor 4 (TLR4)–myeloid differentiation factor 2 (MD2) complex. Surface plasmon resonance analysis indicated that CIRP binds to the TLR4-MD2 complex, as well as to TLR4 and MD2 individually. In particular, human CIRP amino acid residues 106–125 bind to MD2 with high affinity. Thus, CIRP is a damage-associated molecular pattern molecule that promotes inflammatory responses in shock and sepsis.

The ability of cold-adapted bacteria to survive in extreme cold and diverse temperatures is due to their unique attributes like cell membrane stability, up-regulation of peptidoglycan biosynthesis, increased production of extracellular polymeric substances, and expansion of membrane pigment. Various cold-adapted proteins, including ice-nucleating proteins (INPs), antifreeze proteins (AFPs), cold shock proteins (Csps), and cold-acclimated proteins (CAPs), help the bacteria to survive in these environments. To sustain cells from extreme cold conditions and maintain stability in temperature fluctuations, survival strategies at the molecular level and their mechanism play significant roles in adaptations in cryospheric conditions. Furthermore, cold shock domains present in the multifunctional cold shock proteins play crucial roles in their adaptation strategies. The considerable contribution of lipopeptides, osmolytes, and membrane pigments plays an integral part in their survival in extreme environments. This review summarizes the evolutionary history of cold-adapted bacteria and their molecular and cellular adaptation strategies to thrive in harsh cold environments. It also discusses the importance of carotenoids produced, lipid composition, cryoprotectants, proteins, and chaperones related to this adaptation. Furthermore, the functions and mechanisms of adaptations within the cell are discussed briefly. One can utilize and explore their potential in various biotechnology applications and their evolutionary journey by knowing the inherent mechanism of their molecular and cellular adaptation to cold climatic conditions. This review will help all branches of the life science community understand the basic microbiology of psychrophiles and their hidden prospect in life science research.

RNA chaperones play a crucial role in the biogenesis and function of various RNAs in bacteria. They facilitate the interaction of small regulatory trans-encoded sRNAs with mRNAs, thereby significantly altering the pattern of gene expression in cells. This allows bacteria to respond quickly to changing environmental conditions, such as stress or adaptation to host organisms. Despite the identification of a large number of sRNAs in mycobacteria, none of the most common RNA chaperones have been found in their genomes. We determined the crystal structure of the cold shock protein CspB from Mycobacterium tuberculosis. It forms a dimer due to its elongated C-terminal region, which is a hairpin composed of two α-helices. It was also demonstrated that CspB from M. tuberculosis exhibits high affinity for MTS0997 sRNA and MTS1338 sRNA from the same organism, which is consistent with classical RNA chaperons such as Hfq and ProQ. Based on the putative RNA chaperone activity of bacterial proteins with cold-shock domains, we propose that CspB from M. tuberculosis may be involved in the regulation of mycobacterial pathogenesis through interaction with sRNAs.

E. coli has a family of nine homologous cold shock proteins (Csps) of which few members are considered stress proteins. Even with high sequence and structural similarity, not all Csps are expressed after a cold shock, and some are not even considered true Csps. Their designation of “cold shock proteins” is therefore misleading. Understanding their roles could shed light on the necessity of multiple Csps in a single bacterium. This study aims to decipher their expression pattern and understand their probable stress-induced functional roles. We analyzed the transcript abundance of csps in response to conditions of nutrients and stresses of cold, heat, and oxidative. The observations revealed diverse induction patterns, with most stresses inducing the uncharacterized and cold-inducible group. In terms of growth in nutrient media, cspA , cspC, cspD, and cspE have varying induction patterns under a rich and minimal medium, while other csps have a stable expression over the growth phases. In response to cold, along with the cold-inducible group, cspF, and cspH are induced whereas cspC, cspD, and cspE do not have a drastic induction pattern. The cspD , cspH, and cspB are particularly upregulated in response to heat, while the levels of cspC decrease over time. Additionally, exposure to 10mM H 2 O 2 significantly upregulated cspA , cspF, and cspI at 15 min and, along with them, cspC, cspE, and cspH at 30 min. In conclusion, this article describes the novel stress induction pattern of all csps and lays emphasis on cspF and cspH that are still to be assigned a functional role. Therefore, though structurally similar, Csps are differentially expressed and could have stress-induced functional roles within the stress response network of E. coli . Graphical abstract

Cold shock proteins (CSPs) are small, acidic proteins which contain a conserved nucleic acid-binding domain. These perform mRNA translation acting as “RNA chaperones” when triggered by low temperatures initiating their cold shock response. CSP- RNA interactions have been predominantly studied. Our focus will be CSP-DNA interaction examination, to analyse the diverse interaction patterns such as electrostatic, hydrogen and hydrophobic bonding in both thermophilic and mesophilic bacteria. The differences in the molecular mechanism of these contrasting bacterial proteins are studied. Computational techniques such as modelling, energy refinement, simulation and docking were operated to obtain data for comparative analysis. The thermostability factors which stabilise a thermophilic bacterium and their effect on their molecular regulation is investigated. Conformational deviation, atomic residual fluctuations, binding affinity, Electrostatic energy and Solvent Accessibility energy were determined during stimulation along with their conformational study. The study revealed that mesophilic bacteria E. coli CSP have higher binding affinity to DNA than thermophilic G. stearothermophilus . This was further evident by low conformation deviation and atomic fluctuations during simulation. Graphical Abstract

Dehydrins are intrinsically disordered plant proteins whose expression is upregulated under conditions of desiccation and cold stress. Their molecular function in ensuring plant survival is not yet known, but several studies suggest their involvement in membrane stabilization. The dehydrins are characterized by a broad repertoire of conserved and repetitive sequences, out of which the archetypical K-segment has been implicated in membrane binding. To elucidate the molecular mechanism of these K-segments, we examined the interaction between lipid membranes and a dehydrin with a basic functional sequence composition: Lti30, comprising only K-segments. Our results show that Lti30 interacts electrostatically with vesicles of both zwitterionic (phosphatidyl choline) and negatively charged phospholipids (phosphatidyl glycerol, phosphatidyl serine, and phosphatidic acid) with a stronger binding to membranes with high negative surface potential. The membrane interaction lowers the temperature of the main lipid phase transition, consistent with Lti30' s proposed role in cold tolerance. Moreover, the membrane binding promotes the assembly of lipid vesicles into large and easily distinguishable aggregates. Using these aggregates as binding markers, we identify three factors that regulate the lipid interaction of Lti30 in vitro: (1) a pH dependent His on/off switch, (2) phosphorylation by protein kinase C, and (3) reversal of membrane binding by proteolytic digest.

Psychrotrophic foodborne pathogens, such as enteropathogenic Yersinia, which are able to survive and multiply at low temperatures, require cold shock proteins (Csps). The Csp superfamily consists of a diverse group of homologous proteins, which have been found throughout the eubacteria. They are related to cold shock tolerance and other cellular processes. Csps are mainly named following the convention of those in Escherichia coli. However, the nomenclature of certain Csps reflects neither their sequences nor functions, which can be confusing. Here, we performed phylogenetic analyses on Csp sequences in psychrotrophic enteropathogenic Yersinia and E. coli. We found that representative Csps in enteropathogenic Yersinia and E. coli can be clustered into six phylogenetic groups. When we extended the analysis to cover Enterobacteriales, the same major groups formed. Moreover, we investigated the evolutionary and structural relationships and the origin time of Csp superfamily members in eubacteria using nucleotide-level comparisons. Csps in eubacteria were classified into five clades and 12 subclades. The most recent common ancestor of Csp genes was estimated to have existed 3585 million years ago, indicating that Csps have been important since the beginning of evolution and have enabled bacterial growth in unfavorable conditions.

Dehydrins are disordered proteins that are expressed in plants as a response to embryogenesis and water-related stress. The molecular function and structural action of the dehydrins are yet elusive, but increasing evidence points to a role in protecting the structure and functional dynamics of cell membranes. An intriguing example is the cold-induced dehydrin Lti30 that binds to membranes by its conserved K segments. Moreover, this binding can be regulated by pH and phosphorylation and shifts the membrane phase transition to lower temperatures, consistent with the protein's postulated function in cold stress. In this study, we reveal how the Lti30-membrane interplay works structurally at atomic level resolution in Arabidopsis (Arabidopsis thaliana). Nuclear magnetic resonance analysis suggests that negatively charged lipid head groups electrostatically capture the protein's disordered K segments, which locally fold up into α-helical segments on the membrane surface. Thus, Lti30 conforms to the general theme of structure-function relationships by folding upon binding, in spite of its disordered, atypically hydrophilic and repetitive sequence signatures. Moreover, the fixed and well-defined structure of the membrane-bound K segments suggests that dehydrins have the molecular prerequisites for higher level binding specificity and regulation, raising new questions about the complexity of their biological function.

Escherichia coli displays strong adaptability for growth and reproduction at low temperatures, with ribosome biogenesis being a critical process for its growth in cold environments. The cold-shock proteins (CSPs) encompass a protein family that can assist bacterial growth at low temperatures by acting as molecular chaperones. In this study, we investigated whether CSP CspA, CspE, and CspI affect ribosomal RNA (rRNA) transcription. Deletion of the single genes encoding these proteins had only a very marginal effect on cellular growth at low temperatures, and rRNA synthesis was hardly affected. Double and triple deletion of the genes encoding these proteins resulted in a much stronger phenotype providing evidence that CspA, CspE, and CspI play an essential role in maintaining 16S rRNA synthesis and enabling optimal cellular growth at low temperatures. These findings suggest the existence of efficient backup mechanisms able to compensate for the absence of a single CSP.

Both land plants and metazoa have the capacity to reprogram differentiated cells to stem cells. Here we show that the moss Physcomitrella patens Cold-Shock Domain Protein 1 (PpCSP1) regulates reprogramming of differentiated leaf cells to chloronema apical stem cells and shares conserved domains with the induced pluripotent stem cell factor Lin28 in mammals. PpCSP1 accumulates in the reprogramming cells and is maintained throughout the reprogramming process and in the resultant stem cells. Expression of PpCSP1 is negatively regulated by its 3′-untranslated region (3′-UTR). Removal of the 3′-UTR stabilizes PpCSP1 transcripts, results in accumulation of PpCSP1 protein and enhances reprogramming. A quadruple deletion mutant of PpCSP1 and three closely related PpCSP genes exhibits attenuated reprogramming indicating that the PpCSP genes function redundantly in cellular reprogramming. Taken together, these data demonstrate a positive role of PpCSP1 in reprogramming, which is similar to the function of mammalian Lin28. Land plants and metazoans are both able to reprogram differentiated cells to stem cells under certain circumstances. Here the authors show that the moss CSP1 protein, which shares conserved domains with the mammalian pluripotent stem cell factor Lin28, promotes reprogramming of leaf cells to apical stem cells.