Unusual organic osmolytes in deep-sea animals: adaptations to hydrostatic pressure and other perturbants

Associations of current diet with plasma and urine TMAO in the KarMeN study: direct and indirect contributions

SCOPE

Knowledge on the influence of current diet on trimethylamine-N-oxide (TMAO) levels in humans is still inconsistent. Thus, we aimed to investigate associations of current diet with urine and plasma TMAO levels and to determine the effect of different foods on TMAO variation.

METHODS AND RESULTS

TMAO concentrations of 297 healthy individuals were assessed using ¹ H-NMR spectroscopy for 24 h urine collection and spot urine, and LC-MS for plasma. Of 35 assessed food groups, those with a correlation of ρ >|0.15| with plasma or urine TMAO levels were further investigated in multivariate linear regression models showing current fish and (red) meat consumption as plausible dietary sources of TMAO. Overall, explained variance of TMAO levels by current diet and co-variables (age, sex, lean body mass, glomerular filtration rate) was small. Associations with urine and plasma concentrations differed depending on the TMAO source. Fish consumption was associated with urine and plasma TMAO concentrations, whereas meat consumption was only associated with TMAO concentrations in plasma. Furthermore, associations of plasma TMAO concentration with fish consumption were two times stronger than with meat consumption.

CONCLUSION

Meat and fish consumption differentially affects TMAO concentrations in body fluids. Only a small fraction of variance is explained by current diet.

Molecular adaptation in the world's deepest-living animal: Insights from transcriptome sequencing of the hadal amphipod Hirondellea gigas

The Challenger Deep in the Mariana Trench is the deepest point in the oceans of our planet. Understanding how animals adapt to this harsh environment characterized by high hydrostatic pressure, food limitation, dark and cold is of great scientific interest. Of the animals dwelling in the Challenger Deep, amphipods have been captured using baited traps. In this study, we sequenced the transcriptome of the amphipod Hirondellea gigas collected at a depth of 10,929 m from the East Pond of the Challenger Deep. Assembly of these sequences resulted in 133,041 contigs and 22,046 translated proteins. Functional annotation of these contigs was made using the go and kegg databases. Comparison of these translated proteins with those of four shallow-water amphipods revealed 10,731 gene families, of which 5659 were single-copy orthologs. Base substitution analysis on these single-copy orthologs showed that 62 genes are positively selected in H. gigas, including genes related to β-alanine biosynthesis, energy metabolism and genetic information processing. For multiple-copy orthologous genes, gene family expansion analysis revealed that cold-inducible proteins (i.e., transcription factors II A and transcription elongation factor 1) as well as zinc finger domains are expanded in H. gigas. Overall, our results indicate that genetic adaptation to the hadal environment by H. gigas may be mediated by both gene family expansion and amino acid substitutions of specific proteins.

A metabolomic study of biomarkers of meat and fish intake

Background: Meat and fish intakes have been associated with various chronic diseases. The use of specific biomarkers may help to assess meat and fish intake and improve subject classification according to the amount and type of meat or fish consumed.Objective: A metabolomic approach was applied to search for biomarkers of meat and fish intake in a dietary intervention study and in free-living subjects from the European Prospective Investigation into Cancer and Nutrition (EPIC) study.Design: In the dietary intervention study, 4 groups of 10 subjects consumed increasing quantities of chicken, red meat, processed meat, and fish over 3 successive weeks. Twenty-four-hour urine samples were collected during each period and analyzed by high-resolution liquid chromatography-mass spectrometry. Signals characteristic of meat or fish intake were replicated in 50 EPIC subjects for whom a 24-h urine sample and 24-h dietary recall were available and who were selected for their exclusive intake or no intake of any of the 4 same foods.Results: A total of 249 mass spectrometric features showed a positive dose-dependent response to meat or fish intake in the intervention study. Eighteen of these features best predicted intake of the 4 food groups in the EPIC urine samples on the basis of partial receiver operator curve analyses with permutation testing (areas under the curve ranging between 0.61 and 1.0). Of these signals, 8 metabolites were identified. Anserine was found to be specific for chicken intake, whereas trimethylamine-N-oxide showed good specificity for fish. Carnosine and 3 acylcarnitines (acetylcarnitine, propionylcarnitine, and 2-methylbutyrylcarnitine) appeared to be more generic indicators of meat and meat and fish intake, respectively.Conclusion: The meat and fish biomarkers identified in this work may be used to study associations between meat and fish intake and disease risk in epidemiologic studies. This trial was registered at clinicaltrials.gov as NCT01684917.

Hydration structure of osmolyte TMAO: concentration/pressure-induced response

The effect of solute concentration/pressure on the TMAO hydration structure was studied to understand its protective action under abiotic stressors.

Trimethylamine N-Oxide: The Good, the Bad and the Unknown

Trimethylamine N-oxide (TMAO) is a small colorless amine oxide generated from choline, betaine, and carnitine by gut microbial metabolism. It accumulates in the tissue of marine animals in high concentrations and protects against the protein-destabilizing effects of urea. Plasma level of TMAO is determined by a number of factors including diet, gut microbial flora and liver flavin monooxygenase activity. In humans, a positive correlation between elevated plasma levels of TMAO and an increased risk for major adverse cardiovascular events and death is reported. The atherogenic effect of TMAO is attributed to alterations in cholesterol and bile acid metabolism, activation of inflammatory pathways and promotion foam cell formation. TMAO levels increase with decreasing levels of kidney function and is associated with mortality in patients with chronic kidney disease. A number of therapeutic strategies are being explored to reduce TMAO levels, including use of oral broad spectrum antibiotics, promoting the growth of bacteria that utilize TMAO as substrate and the development of target-specific molecules with varying level of success. Despite the accumulating evidence, it is questioned whether TMAO is the mediator of a bystander in the disease process. Thus, it is important to undertake studies examining the cellular signaling in physiology and pathological states in order to establish the role of TMAO in health and disease in humans.

Genomic and physiological analysis reveals versatile metabolic capacity of deep-sea Photobacterium phosphoreum ANT-2200

Bacteria of the genus Photobacterium thrive worldwide in oceans and show substantial eco-physiological diversity including free-living, symbiotic and piezophilic life styles. Genomic characteristics underlying this variability across species are poorly understood. Here we carried out genomic and physiological analysis of Photobacterium phosphoreum strain ANT-2200, the first deep-sea luminous bacterium of which the genome has been sequenced. Using optical mapping we updated the genomic data and reassembled it into two chromosomes and a large plasmid. Genomic analysis revealed a versatile energy metabolic potential and physiological analysis confirmed its growth capacity by deriving energy from fermentation of glucose or maltose, by respiration with formate as electron donor and trimethlyamine N-oxide (TMAO), nitrate or fumarate as electron acceptors, or by chemo-organo-heterotrophic growth in rich media. Despite that it was isolated at a site with saturated dissolved oxygen, the ANT-2200 strain possesses four gene clusters coding for typical anaerobic enzymes, the TMAO reductases. Elevated hydrostatic pressure enhances the TMAO reductase activity, mainly due to the increase of isoenzyme TorA1. The high copy number of the TMAO reductase isoenzymes and pressure-enhanced activity might imply a strategy developed by bacteria to adapt to deep-sea habitats where the instant TMAO availability may increase with depth.

Long-term salinity tolerance is accompanied by major restructuring of the coral bacterial microbiome

Scleractinian corals are assumed to be stenohaline osmoconformers, although they are frequently subjected to variations in seawater salinity due to precipitation, freshwater run-off and other processes. Observed responses to altered salinity levels include differences in photosynthetic performance, respiration and increased bleaching and mortality of the coral host and its algal symbiont, but a study looking at bacterial community changes is lacking. Here, we exposed the coral Fungia granulosa to strongly increased salinity levels in short- and long-term experiments to disentangle temporal and compartment effects of the coral holobiont (i.e. coral host, symbiotic algae and associated bacteria). Our results show a significant reduction in calcification and photosynthesis, but a stable microbiome after short-term exposure to high-salinity levels. By comparison, long-term exposure yielded unchanged photosynthesis levels and visually healthy coral colonies indicating long-term acclimation to high-salinity levels that were accompanied by a major coral microbiome restructuring. Importantly, a bacterium in the family Rhodobacteraceae was succeeded by Pseudomonas veronii as the numerically most abundant taxon. Further, taxonomy-based functional profiling indicates a shift in the bacterial community towards increased osmolyte production, sulphur oxidation and nitrogen fixation. Our study highlights that bacterial community composition in corals can change within days to weeks under altered environmental conditions, where shifts in the microbiome may enable adjustment of the coral to a more advantageous holobiont composition.

Hydration structure of trimethylamine N-oxide in aqueous solutions revealed by soft X-ray emission spectroscopy and chemometric analysis

Soft X-ray emission spectroscopy coupled with a quantitative spectral analysis offers a useful technique for probing the solvation structure around the solute which interacts strongly with the solvent.

Downregulation of hepatic betaine:homocysteine methyltransferase (BHMT) expression in taurine-deficient mice is reversed by taurine supplementation in vivo

The cysteine dioxygenase (Cdo1)-null and the cysteine sulfinic acid decarboxylase (Csad)-null mouse are not able to synthesize hypotaurine/taurine by the cysteine/cysteine sulfinate pathway and have very low tissue taurine levels. These mice provide excellent models for studying the effects of taurine on biological processes. Using these mouse models, we identified betaine:homocysteine methyltransferase (BHMT) as a protein whose in vivo expression is robustly regulated by taurine. BHMT levels are low in liver of both Cdo1-null and Csad-null mice, but are restored to wild-type levels by dietary taurine supplementation. A lack of BHMT activity was indicated by an increase in the hepatic betaine level. In contrast to observations in liver of Cdo1-null and Csad-null mice, BHMT was not affected by taurine supplementation of primary hepatocytes from these mice. Likewise, CSAD abundance was not affected by taurine supplementation of primary hepatocytes, although it was robustly upregulated in liver of Cdo1-null and Csad-null mice and lowered to wild-type levels by dietary taurine supplementation. The mechanism by which taurine status affects hepatic CSAD and BHMT expression appears to be complex and to require factors outside of hepatocytes. Within the liver, mRNA abundance for both CSAD and BHMT was upregulated in parallel with protein levels, indicating regulation of BHMT and CSAD mRNA synthesis or degradation.

Proteomic analysis of the European flounder Platichthys flesus response to experimental PAH-PCB contamination

Platichthys flesus is often used as a sentinel species to monitor the estuarine water quality. In this study, we carried out an experimental contamination of fish using a PAHs/PCBs mixture, which was designed to mimic the concentrations found in the Seine estuary (C1) and 10 times these concentrations (C2). We used a proteomic approach to understand the molecular mechanisms implied in the response of P. flesus to these xenobiotics. We showed that 54 proteins were differentially accumulated in one or several conditions, which 34 displayed accumulation factors higher than two. 18 of these proteins were identified by MALDI TOF-TOF mass spectrometry. The results indicated the deregulation of oxidative stress- and glutathione metabolism-(GST, GPx) proteins as well as of several proteins belonging to the betaine demethylation pathway and the methionine cycle (BHMT, SHMT, SAHH), suggesting a role for these different pathways in the P. flesus response to chemical contamination.

Modelling of noble anaesthetic gases and high hydrostatic pressure effects in lipid bilayers

Our objective was to study molecular processes that might be responsible for inert gas narcosis and high-pressure nervous syndrome. The classical molecular dynamics trajectories (200 ns) of dioleoylphosphatidylcholine (DOPC) bilayers simulated by the Berger force field were evaluated for water and the atomic distribution of noble gases around DOPC molecules in the pressure range of 1-1000 bar and at a temperature of 310 K. Xenon and argon have been tested as model gases for general anaesthetics, and neon has been investigated for distortions that are potentially responsible for neurological tremors in hyperbaric conditions. The analysis of stacked radial pair distribution functions of DOPC headgroup atoms revealed the explicit solvation potential of the gas molecules, which correlates with their dimensions. The orientational dynamics of water molecules at the biomolecular interface should be considered as an influential factor, while excessive solvation effects appearing in the lumen of membrane-embedded ion channels could be a possible cause of inert gas narcosis. All the noble gases tested exhibit similar order parameter patterns for both DOPC acyl chains, which are opposite of the patterns found for the order parameter curve at high hydrostatic pressures in intact bilayers. This finding supports the 'critical volume' hypothesis of anaesthesia pressure reversal. The irregular lipid headgroup-water boundary observed in DOPC bilayers saturated with neon in the pressure range of 1-100 bar could be associated with the possible manifestation of neurological tremors at the atomic scale. The non-immobiliser neon also demonstrated the highest momentum impact on the normal component of the DOPC diffusion coefficient representing the monolayer undulation rate, which indicates that enhanced diffusivity rather than atomic size is the key factor.

Differential metabolite levels in response to spawning-induced inappetence in Atlantic salmon Salmo salar

Atlantic salmon Salmo salar undergo months-long inappetence during spawning, but it is not known whether this inappetence is a pathological state or one for which the fish are adapted. Recent work has shown that inappetent whale sharks can exhibit circulating metabolite profiles similar to ketosis known to occur in humans during starvation. In this work, metabolite profiling was used to explore differences in analyte profiles between a cohort of inappetent spawning run Atlantic salmon and captively reared animals that were fed up to and through the time of sampling. The two classes of animals were easily distinguished by their metabolite profiles. The sea-run fish had elevated ɷ-9 fatty acids relative to the domestic feeding animals, while other fatty acid concentrations were reduced. Sugar alcohols were generally elevated in inappetent animals, suggesting potentially novel metabolic responses or pathways in fish that feature these compounds. Compounds expected to indicate a pathological catabolic state were not more abundant in the sea-run fish, suggesting that the animals, while inappetent, were not stressed in an unnatural way. These findings demonstrate the power of discovery-based metabolomics for exploring biochemistry in poorly understood animal models.

Are stabilizing osmolytes preferentially excluded from the protein surface? FTIR and MD studies

Stabilizing osmolytes are not always preferentially excluded and can interact with the protein surface in two ways: indirectly or directly.

Transcriptome of the Deep-Sea Black Scabbardfish, Aphanopus carbo (Perciformes: Trichiuridae): Tissue-Specific Expression Patterns and Candidate Genes Associated to Depth Adaptation

Deep-sea fishes provide a unique opportunity to study the physiology and evolutionary adaptation to extreme environments. We carried out a high throughput sequencing analysis on a 454 GS-FLX titanium plate using unnormalized cDNA libraries from six tissues of A. carbo. Assemblage and annotations were performed by Newbler and InterPro/Pfam analyses, respectively. The assembly of 544,491 high quality reads provided 8,319 contigs, 55.6% of which retrieved blast hits against the NCBI nonredundant database or were annotated with ESTscan. Comparison of functional genes at both the protein sequences and protein stability levels, associated with adaptations to depth, revealed similarities between A. carbo and other bathypelagic fishes. A selection of putative genes was standardized to evaluate the correlation between number of contigs and their normalized expression, as determined by qPCR amplification. The screening of the libraries contributed to the identification of new EST simple-sequence repeats (SSRs) and to the design of primer pairs suitable for population genetic studies as well as for tagging and mapping of genes. The characterization of the deep-sea fish A. carbo first transcriptome is expected to provide abundant resources for genetic, evolutionary, and ecological studies of this species and the basis for further investigation of depth-related adaptation processes in fishes.

Explaining bathymetric diversity patterns in marine benthic invertebrates and demersal fishes: physiological contributions to adaptation of life at depth

Bathymetric biodiversity patterns of marine benthic invertebrates and demersal fishes have been identified in the extant fauna of the deep continental margins. Depth zonation is widespread and evident through a transition between shelf and slope fauna from the shelf break to 1000 m, and a transition between slope and abyssal fauna from 2000 to 3000 m; these transitions are characterised by high species turnover. A unimodal pattern of diversity with depth peaks between 1000 and 3000 m, despite the relatively low area represented by these depths. Zonation is thought to result from the colonisation of the deep sea by shallow-water organisms following multiple mass extinction events throughout the Phanerozoic. The effects of low temperature and high pressure act across hierarchical levels of biological organisation and appear sufficient to limit the distributions of such shallow-water species. Hydrostatic pressures of bathyal depths have consistently been identified experimentally as the maximum tolerated by shallow-water and upper bathyal benthic invertebrates at in situ temperatures, and adaptation appears required for passage to deeper water in both benthic invertebrates and demersal fishes. Together, this suggests that a hyperbaric and thermal physiological bottleneck at bathyal depths contributes to bathymetric zonation. The peak of the unimodal diversity-depth pattern typically occurs at these depths even though the area represented by these depths is relatively low. Although it is recognised that, over long evolutionary time scales, shallow-water diversity patterns are driven by speciation, little consideration has been given to the potential implications for species distribution patterns with depth. Molecular and morphological evidence indicates that cool bathyal waters are the primary site of adaptive radiation in the deep sea, and we hypothesise that bathymetric variation in speciation rates could drive the unimodal diversity-depth pattern over time. Thermal effects on metabolic-rate-dependent mutation and on generation times have been proposed to drive differences in speciation rates, which result in modern latitudinal biodiversity patterns over time. Clearly, this thermal mechanism alone cannot explain bathymetric patterns since temperature generally decreases with depth. We hypothesise that demonstrated physiological effects of high hydrostatic pressure and low temperature at bathyal depths, acting on shallow-water taxa invading the deep sea, may invoke a stress-evolution mechanism by increasing mutagenic activity in germ cells, by inactivating canalisation during embryonic or larval development, by releasing hidden variation or mutagenic activity, or by activating or releasing transposable elements in larvae or adults. In this scenario, increased variation at a physiological bottleneck at bathyal depths results in elevated speciation rate. Adaptation that increases tolerance to high hydrostatic pressure and low temperature allows colonisation of abyssal depths and reduces the stress-evolution response, consequently returning speciation of deeper taxa to the background rate. Over time this mechanism could contribute to the unimodal diversity-depth pattern.

Strategy of metabolic phenotype modulation in Portunus trituberculatus exposed to low salinity

Extreme low salinity influences normal crab growth, morphogenesis, and production. Some individuals of swimming crab Portunus trituberculatus have, however, an inherent ability to adapt to such a salinity fluctuation. This study investigated the dynamic metabolite alterations of two P. trituberculatus strains, namely, a wild one and a screened (low-salinity tolerant) one in response to low-salinity challenge by combined use of NMR spectroscopy and high-throughput data analysis. The dominant metabolites in crab muscle were found to comprise amino acids, sugars, carboxylic acids, betaine, trimethylamine-N-oxide, 2-pyridinemethanol, trigonelline, and nucleotides. These results further showed that the strategy of metabolic modulation of P. trituberculatus after low-salinity stimulus includes osmotic rebalancing, enhanced gluconeogenesis from amino acids, and energy accumulation. These metabolic adaptations were manifested in the accumulation of trimethylamine-N-oxide, ATP, 2-pyridinemethanol, and trigonelline and in the depletion of the amino acid pool as well as in the fluctuation of inosine levels. This lends support to the fact that the low-salinity training accelerates the responses of crabs to low-salinity stress. These findings provide a comprehensive insight into the mechanisms of metabolic modulation in P. trituberculatus in response to low salinity. This work highlights the approach of NMR-based metabonomics in conjunction with multivariate data analysis and univariate data analysis in understanding the strategy of metabolic phenotype modulation against stressors.

Marine fish may be biochemically constrained from inhabiting the deepest ocean depths

No fish have been found in the deepest 25% of the ocean (8,400-11,000 m). This apparent absence has been attributed to hydrostatic pressure, although direct evidence is wanting because of the lack of deepest-living species to study. The common osmolyte trimethylamine N-oxide (TMAO) stabilizes proteins against pressure and increases with depth, going from 40 to 261 mmol/kg in teleost fishes from 0 to 4,850 m. TMAO accumulation with depth results in increasing internal osmolality (typically 350 mOsmol/kg in shallow species compared with seawater's 1,100 mOsmol/kg). Preliminary extrapolation of osmolalities of predicted isosmotic state at 8,000-8,500 m may indicate a possible physiological limit, as greater depths would require reversal of osmotic gradients and, thus, osmoregulatory systems. We tested this prediction by capturing five of the second-deepest known fish, the hadal snailfish (Notoliparis kermadecensis; Liparidae), from 7,000 m in the Kermadec Trench. We found their muscles to have a TMAO content of 386 ± 18 mmol/kg and osmolality of 991 ± 22 mOsmol/kg. These data fit previous extrapolations and, combined with new osmolalities from bathyal and abyssal fishes, predict isosmotic state at 8,200 m. This is previously unidentified evidence that biochemistry could constrain the depth of a large, complex taxonomic group.

N-Methyltaurine N-acyl amidated bile acids and deoxycholic acid in the bile of angelfish (Pomacanthidae): a novel bile acid profile in Perciform fish

Two novel N-acyl amidated bile acids, N-methyltaurine conjugated cholic acid and N-methyltaurine conjugated deoxycholic acid, were found to be major biliary bile acids in two species of angelfish the regal (Pygoplites diacanthus) and the blue-girdled (Pomacanthus navarchus) angelfish. The identification was based on their having MS and NMR spectra identical to those of synthetic standards. A survey of biliary bile acids of 10 additional species of angelfish found 7 with N-methyltaurine conjugation. In all 12 species, conjugated deoxycholic acid (known to be formed by bacterial 7-dehydroxylation of cholic acid) was a major bile acid. In all previous studies of biliary bile acids in fish, deoxycholic acid has been present in only trace proportions. In addition, bile acid conjugation with N-methyltaurine has not been detected previously in any known vertebrate. N-methyltaurine conjugated bile acids are resistant to bacterial deconjugation and dehydroxylation, and such resistance to bacterial enzymes should aid in the maintenance of high concentrations of bile acids during lipid digestion. Our findings suggest that these species of angelfish have a novel microbiome in their intestine containing anaerobic bacteria, and describe the presence of N-methyltaurine conjugated bile acids that are resistant to bacterial attack.

Effect of TMAO and betaine on the energy landscape of photosystem I

The accumulation of organic co-solvents in cells is a basic strategy for organisms from various species to increase stress tolerance in extreme environments. Widespread representatives of this class of co-solvents are trimethylamine-N-oxide (TMAO) and betaine; these small molecules are able to stabilize the native conformation of proteins and prevent their aggregation. Despite their importance, detailed experimental studies on the impact of these co-solvents on the energy landscape of proteins have not yet been carried out. We use single-molecule spectroscopy at cryogenic temperatures to examine the influence of these physiological relevant co-solvents on photosystem I (PSI) from Thermosynechococcus elongatus. In contrast to PSI ensemble spectra, which are almost unaffected by the addition of TMAO and betaine, statistical analysis of the fluorescence emission from individual PSI trimers yields insight into the interaction of the co-solvents with PSI. The results show an increased homogeneity upon addition of TMAO or betaine. The number of detectable zero-phonon lines (ZPLs) is reduced, indicating spectral diffusion processes with faster rates. In the framework of energy landscape model these findings indicate that co-solvents lead to reduced barrier heights between energy valleys, and thus efficient screening of protein conformations can take place.

Discovery of a substrate selectivity motif in amino acid decarboxylases unveils a taurine biosynthesis pathway in prokaryotes

Taurine, the most abundant free amino acid in mammals, with many critical roles such as neuronal development, had so far only been reported to be synthetized in eukaryotes. Taurine is the major product of cysteine metabolism in mammals, and its biosynthetic pathway consists of cysteine dioxygenase and cysteine sulfinic acid decarboxylase (hCSAD). Sequence, structural, and mutational analyses of the structurally and sequentially related hCSAD and human glutamic acid decarboxylase (hGAD) enzymes revealed a three residue substrate recognition motif (X1aa19X2aaX3), within the active site that is responsible for coordinating their respective preferred amino acid substrates. Introduction of the cysteine sulfinic acid (CSA) motif into hGAD (hGAD-S192F/N212S/F214Y) resulted in an enzyme with a >700 fold switch in selectivity toward the decarboxylation of CSA over its preferred substrate, l-glutamic acid. Surprisingly, we found this CSA recognition motif in the genome sequences of several marine bacteria, prompting us to evaluate the catalytic properties of bacterial amino acid decarboxylases that were predicted by sequence motif to decarboxylate CSA but had been annotated as GAD enzymes. We show that CSAD from Synechococcus sp. PCC 7335 specifically decarboxylated CSA and that the bacteria accumulated intracellular taurine. The fact that CSAD homologues exist in certain bacteria and are frequently found in operons containing the recently discovered bacterial cysteine dioxygenases that oxidize l-cysteine to CSA supports the idea that a bona fide bacterial taurine biosynthetic pathway exists in prokaryotes.

The effect of hydration state and energy balance on innate immunity of a desert reptile

Introduction

Immune function is a vital physiological process that is often suppressed during times of resource scarcity due to investments in other physiological systems. While energy is the typical currency that has been examined in such trade-offs, limitations of other resources may similarly lead to trade-offs that affect immune function. Specifically, water is a critical resource with profound implications for organismal ecology, yet its availability can fluctuate at local, regional, and even global levels. Despite this, the effect of osmotic state on immune function has received little attention.

Results

Using agglutination and lysis assays as measures of an organism’s plasma concentration of natural antibodies and capacity for foreign cell destruction, respectively, we tested the independent effects of osmotic state, digestive state, and energy balance on innate immune function in free-ranging and laboratory populations of the Gila monster, Heloderma suspectum. This desert-dwelling lizard experiences dehydration and energy resource fluctuations on a seasonal basis. Dehydration was expected to decrease innate immune function, yet we found that dehydration increased lysis and agglutination abilities in both lab and field studies, a relationship that was not simply an effect of an increased concentration of immune molecules. Laboratory-based differences in digestive state were not associated with lysis or agglutination metrics, although in our field population, a loss of fat stores was correlated with an increase in lysis.

Conclusions

Depending on the life history of an organism, osmotic state may have a greater influence on immune function than energy availability. Thus, consideration of osmotic state as a factor influencing immune function will likely improve our understanding of ecoimmunology and the disease dynamics of a wide range of species.

Paracoccus denitrificans PD1222 utilizes hypotaurine via transamination followed by spontaneous desulfination to yield acetaldehyde and, finally, acetate for growth

Hypotaurine (HT; 2-aminoethane-sulfinate) is known to be utilized by bacteria as a sole source of carbon, nitrogen, and energy for growth, as is taurine (2-aminoethane-sulfonate); however, the corresponding HT degradation pathway has remained undefined. Genome-sequenced Paracoccus denitrificans PD1222 utilized HT (and taurine) quantitatively for heterotrophic growth and released the HT sulfur as sulfite (and sulfate) and HT nitrogen as ammonium. Enzyme assays with cell extracts suggested that an HT-inducible HT:pyruvate aminotransferase (Hpa) catalyzes the deamination of HT in an initial reaction step. Partial purification of the Hpa activity and peptide fingerprinting-mass spectrometry (PF-MS) identified the Hpa candidate gene; it encoded an archetypal taurine:pyruvate aminotransferase (Tpa). The same gene product was identified via differential PAGE and PF-MS, as was the gene of a strongly HT-inducible aldehyde dehydrogenase (Adh). Both genes were overexpressed in Escherichia coli. The overexpressed, purified Hpa/Tpa showed HT:pyruvate-aminotransferase activity. Alanine, acetaldehyde, and sulfite were identified as the reaction products but not sulfinoacetaldehyde; the reaction of Hpa/Tpa with taurine yielded sulfoacetaldehyde, which is stable. The overexpressed, purified Adh oxidized the acetaldehyde generated during the Hpa reaction to acetate in an NAD(+)-dependent reaction. Based on these results, the following degradation pathway for HT in strain PD1222 can be depicted. The identified aminotransferase converts HT to sulfinoacetaldehyde, which desulfinates spontaneously to acetaldehyde and sulfite; the inducible aldehyde dehydrogenase oxidizes acetaldehyde to yield acetate, which is metabolized, and sulfite, which is excreted.

The effect of chemical chaperones on the assembly and stability of HIV-1 capsid protein

Chemical chaperones are small organic molecules which accumulate in a broad range of organisms in various tissues under different stress conditions and assist in the maintenance of a correct proteostasis under denaturating environments. The effect of chemical chaperones on protein folding and aggregation has been extensively studied and is generally considered to be mediated through non-specific interactions. However, the precise mechanism of action remains elusive. Protein self-assembly is a key event in both native and pathological states, ranging from microtubules and actin filaments formation to toxic amyloids appearance in degenerative disorders, such as Alzheimer's and Parkinson's diseases. Another pathological event, in which protein assembly cascade is a fundamental process, is the formation of virus particles. In the late stage of the virus life cycle, capsid proteins self-assemble into highly-ordered cores, which encapsulate the viral genome, consequently protect genome integrity and mediate infectivity. In this study, we examined the effect of different groups of chemical chaperones on viral capsid assembly in vitro, focusing on HIV-1 capsid protein as a system model. We found that while polyols and sugars markedly inhibited capsid assembly, methylamines dramatically enhanced the assembly rate. Moreover, chemical chaperones that inhibited capsid core formation, also stabilized capsid structure under thermal denaturation. Correspondingly, trimethylamine N-oxide, which facilitated formation of high-order assemblies, clearly destabilized capsid structure under similar conditions. In contrast to the prevailing hypothesis suggesting that chemical chaperones affect proteins through preferential exclusion, the observed dual effects imply that different chaperones modify capsid assembly and stability through different mechanisms. Furthermore, our results indicate a correlation between the folding state of capsid to its tendency to assemble into highly-ordered structures.

In vivo detection and quantification of chemicals that enhance protein stability

We have devised protein-folding sensors that link protein stability to TEM-1 β-lactamase activity. The addition of osmolytes and other compounds with chemical chaperone activity to the growth medium of bacteria containing these sensors increases β-lactamase activity up to 207-fold in a dose-dependent manner. This enables the rapid detection and sensitive quantification of compounds that enhance in vivo protein stability.

Stabilization of the predominant disease-causing aldolase variant (A149P) with zwitterionic osmolytes

Hereditary fructose intolerance (HFI) is a disease of carbohydrate metabolism that can result in hyperuricemia, hypoglycemia, liver and kidney failure, coma, and death. Currently, the only treatment for HFI is a strict fructose-free diet. HFI arises from aldolase B deficiency, and the most predominant HFI mutation is an alanine to proline substitution at position 149 (A149P). The resulting aldolase B with the A149P substitution (AP-aldolase) has activity that is <100-fold that of the wild type. The X-ray crystal structure of AP-aldolase at both 4 and 18 °C reveals disordered adjacent loops of the (α/β)(8) fold centered around the substitution, which leads to a dimeric structure as opposed to the wild-type tetramer. The effects of osmolytes were tested for restoration of structure and function. An initial screen of osmolytes (glycerol, sucrose, polyethylene glycol, 2,4-methylpentanediol, glutamic acid, arginine, glycine, proline, betaine, sarcosine, and trimethylamine N-oxide) reveals that glycine, along with similarly structured compounds, betaine and sarcosine, protects AP-aldolase structure and activity from thermal inactivation. The concentration and functional moieties required for thermal protection show a zwitterion requirement. The effects of osmolytes in restoring structure and function of AP-aldolase are described. Testing of zwitterionic osmolytes of increasing size and decreasing fractional polar surface area suggests that osmolyte-mediated AP-aldolase stabilization occurs neither primarily through excluded volume effects nor through transfer free energy effects. These data suggest that AP-aldolase is stabilized by binding to the native structure, and they provide a foundation for developing stabilizing compounds for potential therapeutics for HFI.

High-pressure adaptation of muscle proteins from deep-sea fishes, Coryphaenoides yaquinae and C. armatus

The evolutionary adaptations of functional genes to life at high pressures are not well understood. To elucidate the mechanisms of protein adaptation to high pressures, we isolated two muscle protein-encoding cDNAs, alpha-actin and myosin heavy chain (MyHC), derived from skeletal muscles of two deep-sea fishes, Coryphaenoides yaquinae and C. armatus, and two non-deep-sea fishes, C. acrolepis and C. cinereus. The alpha-actins from two deep-sea fishes have three amino acid substitutions in comparison to those of non-deep-sea fishes. These substitutions enable the deep-sea fish actins to function even at 60 MPa. The MyHCs of the two deep-sea fishes have a proline residue in the loop-1 region and have a shorter loop-2 region than the non-deep-sea fishes. Additionally, the MyHCs of deep-sea fishes have biased amino acid substitutions at core positions within the coiled-coil structure of the rod region. The roles of these substitutions in the deep-sea fishes MyHCs, however, remain unclear.

Isethionate formation from taurine in Chromohalobacter salexigens: purification of sulfoacetaldehyde reductase

Bacterial generation of isethionate (2-hydroxyethanesulfonate) from taurine (2-aminoethanesulfonate) by anaerobic gut bacteria was established in 1980. That phenomenon in pure culture was recognized as a pathway of assimilation of taurine-nitrogen. Based on the latter work, we predicted from genome-sequence data that the marine gammaproteobacterium Chromohalobacter salexigens DSM 3043 would exhibit this trait. Quantitative conversion of taurine to isethionate, identified by mass spectrometry, was confirmed, and the taurine-nitrogen was recovered as cell material. An eight-gene cluster was predicted to encode the inducible vectorial, scalar and regulatory enzymes involved, some of which were known from other taurine pathways. The genes (Csal_0153-Csal_0156) encoding a putative ATP-binding-cassette (ABC) transporter for taurine (TauAB(1)B(2)C) were shown to be inducibly transcribed by reverse transcription (RT-) PCR. An inducible taurine : 2-oxoglutarate aminotransferase [EC 2.6.1.55] was found (Csal_0158); the reaction yielded glutamate and sulfoacetaldehyde. The sulfoacetaldehyde was reduced to isethionate by NADPH-dependent sulfoacetaldehyde reductase (IsfD), a member of the short-chain alcohol dehydrogenase superfamily. The 27 kDa protein (SDS-PAGE) was identified by peptide-mass fingerprinting as the gene product of Csal_0161. The putative exporter of isethionate (IsfE) is encoded by Csal_0160; isfE was inducibly transcribed (RT-PCR). The presumed transcriptional regulator, TauR (Csal_0157), may autoregulate its own expression, typical of GntR-type regulators. Similar gene clusters were found in several marine and terrestrial gammaproteobacteria, which, in the gut canal, could be the source of not only mammalian, but also arachnid and cephalopod isethionate.

Hypotaurine and sulfhydryl-containing antioxidants reduce H2S toxicity in erythrocytes from a marine invertebrate

Hypotaurine (HT) has been proposed to reduce sulfide toxicity in some deep-sea invertebrates by scavenging free radicals produced from sulfide oxidation or by scavenging sulfide via the reaction of HT with sulfide, forming thiotaurine (ThT). We tested whether HT or several antioxidants could reduce the total dissolved sulfide concentration in buffered seawater exposed to H2S, and whether HT, ThT or antioxidants could increase the viability of Glycera dibranchiataerythrocytes exposed to H2S in vitro. We found that 5 and 50 mmol l–1 HT reduced the dissolved sulfide in cell-free buffer exposed to H2S by up to 80% whereas the antioxidants glutathione ethyl ester (GEE), N-acetylcysteine (NAC), l-ascorbic acid (ASC), Tempol and Trolox had no consistent effect. Exposure of erythrocytes to 0.10%–3.2% H2S (producing 0.18–4.8 mmol l–1 sulfide) decreased the fraction of viable cells, as evidenced by loss of plasma membrane integrity, with virtually no cells remaining viable at 1.0% or more H2S. Addition of HT (0.5–50 mmol l–1) significantly increased the fraction of viable cells (e.g. from 0.01 to 0.84 at 0.32% H2S) whereas ThT (0.5 and 5 mmol l–1) decreased cell viability. GEE (0.03–3 mmol l–1) and NAC (0.001–1 mmol l–1), which contain sulfhydryl groups, increased cell viability during H2S exposure but to a lesser extent than HT whereas ASC, Tempol and Trolox, which do not contain sulfhydryl groups, decreased viability or had no effect. These data show that HT can protect cells from sulfide in vitro and suggest that sulfide scavenging, rather than free radical scavenging, is the most important mechanism of protection.

Comparative sequence analysis of myosin heavy chain proteins from congeneric shallow- and deep-living rattail fish (genus Coryphaenoides)

The evolutionary adaptations of functional genes to life at high pressure are not well understood. To elucidate the mechanisms of protein adaptation to high pressure, we cloned the myosin heavy chain (MyHC) cDNA from skeletal muscle of two deep-sea fishes, Coryphaenoides yaquinae and C. armatus, and two non-deep-sea fishes, C. acrolepis and C. cinereus. The MyHCs of deep-sea fishes have a unique structure in two loop regions, loop-1 and loop-2, in comparison with those of non-deep-sea fishes. The loop-1 region of deep-sea fishes has a Pro residue and the loop-2 region, which is an actin-binding site, is shorter than the same region in non-deep-sea fishes. The amino acid substitution in the loop-1 region is expected to be mainly involved in ATPase activity, whereas the deletion in the loop-2 region affects the association of MyHC with actin filaments at high pressure. In addition, the MyHC of deep-sea fishes has biased amino acid substitutions at core positions in the coiled-coil structure of the rod region. These amino acid substitutions are likely to decrease the cavities in the coiled-coil structure and consequently make the structure more compact and unaffected by high pressure. Together, these results indicate that amino acid substitutions can adaptively alter the pressure sensitivity of a protein even if they do not directly influence core structure.

Central mechanisms of osmosensation and systemic osmoregulation

Systemic osmoregulation is a vital process whereby changes in plasma osmolality, detected by osmoreceptors, modulate ingestive behaviour, sympathetic outflow and renal function to stabilize the tonicity and volume of the extracellular fluid. Furthermore, changes in the central processing of osmosensory signals are likely to affect the hydro-mineral balance and other related aspects of homeostasis, including thermoregulation and cardiovascular balance. Surprisingly little is known about how the brain orchestrates these responses. Here, recent advances in our understanding of the molecular, cellular and network mechanisms that mediate the central control of osmotic homeostasis in mammals are reviewed.

Sulfoacetate released during the assimilation of taurine-nitrogen by Neptuniibacter caesariensis: purification of sulfoacetaldehyde dehydrogenase

Taurine (2-aminoethanesulfonate) is a widespread natural product whose nitrogen moiety was recently shown to be assimilated by bacteria, usually with excretion of an organosulfonate via undefined novel pathways; other data involve transcriptional regulator TauR in taurine metabolism. A screen of genome sequences for TauR with the BLAST algorithm allowed the hypothesis that the marine gammaproteobacterium Neptuniibacter caesariensis MED92 would inducibly assimilate taurine-nitrogen and excrete sulfoacetate. The pathway involved an ABC transporter (TauABC), taurine:pyruvate aminotransferase (Tpa), a novel sulfoacetaldehyde dehydrogenase (SafD) and exporter(s) of sulfoacetate (SafE) (DUF81). Ten candidate genes in two clusters involved three sets of paralogues (for TauR, Tpa and SafE). Inducible Tpa and SafD were detected in cell extracts. SafD was purified 600-fold to homogeneity in two steps. The monomer had a molecular mass of 50 kDa (SDS-PAGE); data from gel filtration chromatography indicated a tetrameric native protein. SafD was specific for sulfoacetaldehyde with a K (m)-value of 0.12 mM. The N-terminal amino acid sequence of SafD confirmed the identity of the safD gene. The eight pathway genes were transcribed inducibly, which indicated expression of the whole hypothetical pathway. We presume that this pathway is one source of sulfoacetate in nature, where this compound is dissimilated by many bacteria.

Intracellular organic osmolytes: function and regulation

Cells of almost all organisms accumulate organic osmolytes when exposed to hyperosmolality, most often in the form of high salt or urea. In this review, we discuss 1) how the organic osmolytes protect; 2) the identity of osmolytes in Archaea, bacteria, yeast, plants, marine animals, and mammals; 3) the mechanisms by which they are accumulated; 4) sensors of osmolality; 5) the signaling pathways involved; and 6) mutual counteraction by urea and methylamines.

Intracellular organic osmolytes: function and regulation

Cells of almost all organisms accumulate organic osmolytes when exposed to hyperosmolality, most often in the form of high salt or urea. In this review, we discuss 1) how the organic osmolytes protect; 2) the identity of osmolytes in Archaea, bacteria, yeast, plants, marine animals, and mammals; 3) the mechanisms by which they are accumulated; 4) sensors of osmolality; 5) the signaling pathways involved; and 6) mutual counteraction by urea and methylamines.