Low temperature persistence of type I antifreeze protein is mediated by cold-specific mRNA stability

The Glaciozyma antarctica genome reveals an array of systems that provide sustained responses towards temperature variations in a persistently cold habitat

Extremely low temperatures present various challenges to life that include ice formation and effects on metabolic capacity. Psyhcrophilic microorganisms typically have an array of mechanisms to enable survival in cold temperatures. In this study, we sequenced and analysed the genome of a psychrophilic yeast isolated in the Antarctic region, Glaciozyma antarctica. The genome annotation identified 7857 protein coding sequences. From the genome sequence analysis we were able to identify genes that encoded for proteins known to be associated with cold survival, in addition to annotating genes that are unique to G. antarctica. For genes that are known to be involved in cold adaptation such as anti-freeze proteins (AFPs), our gene expression analysis revealed that they were differentially transcribed over time and in response to different temperatures. This indicated the presence of an array of adaptation systems that can respond to a changing but persistent cold environment. We were also able to validate the activity of all the AFPs annotated where the recombinant AFPs demonstrated anti-freeze capacity. This work is an important foundation for further collective exploration into psychrophilic microbiology where among other potential, the genes unique to this species may represent a pool of novel mechanisms for cold survival.

Activation of Ice Recrystallization Inhibition Activity of Poly(vinyl alcohol) using a Supramolecular Trigger

Antifreeze (glyco)proteins (AF(G)Ps) have potent ice recrystallisation inhibition (IRI) activity - a desirable phenomenon in applications such as cryopreservation, frozen food and more. In Nature AF(G)P activity is regulated by protein expression levels in response to an environmental stimulus; temperature. However, this level of regulation is not possible in synthetic systems. Here, a synthetic macromolecular mimic is introduced, using supramolecular assembly to regulate activity. Catechol-terminated poly(vinyl alcohol) was synthesised by RAFT polymerization. Upon addition of Fe3+, larger supramolecular star polymers form by assembly with two or three catechols. This increase in molecular weight effectively 'switches on' the IRI activity and is the first example of external control over the function of AFP mimetics. This provides a simple but elegant solution to the challenge of external control of AFP-mimetic function.

Temperature has a major influence on cardiac natriuretic peptide in salmon

1. Natriuretic peptides have a major role in fluid and electrolyte homeostasis in vertebrates. Ambient temperature has a major influence on physiological processes in ectothermic animals. Here we have studied the mechanisms of regulation of a natriuretic peptide, sCP (salmon cardiac peptide), in salmon (Salmo salar) acclimatised and acclimated to varying temperatures. 2. The circulating and cardiac levels of sCP were found to be markedly upregulated in warm-acclimatised and warm-acclimated salmon. The release of sCP from isolated in vitro perfused salmon ventricle was, however, not increased by acclimation to higher temperatures, either in basal conditions or when stimulated by mechanical load. 3. Concomitant measurements of circulating sCP and the biologically inert N-terminal fragment of pro-sCP showed that the upregulation of circulating sCP at warm ambient temperature results from decreased elimination rather than increased secretion of sCP. This is the first direct evidence that changes in the elimination of a natriuretic peptide are used for important physiological regulation. 4. We found a paradoxical increase in cardiac sCP mRNA levels at cold temperatures which coincided with hypertrophy of the heart. sCP gene expression may therefore serve as a marker of cardiac hypertrophy in salmon, in analogy to that of atrial and brain natriuretic peptide (ANP and BNP, respectively) in mammals. 5. These results show that temperature has a major influence on the regulation of natriuretic peptide production and clearance in salmon. Salmon CP offers a novel model for the study of the endocrine function of the heart.

Antifreeze proteins of teleost fishes

Marine teleosts at high latitudes can encounter ice-laden seawater that is approximately 1 degrees C colder than the colligative freezing point of their body fluids. They avoid freezing by producing small antifreeze proteins (AFPs) that adsorb to ice and halt its growth, thereby producing an additional non-colligative lowering of the freezing point. AFPs are typically secreted by the liver into the blood. Recently, however, it has become clear that AFP isoforms are produced in the epidermis (skin, scales, fin, and gills) and may serve as a first line of defense against ice propagation into the fish. The basis for the adsorption of AFPs to ice is something of a mystery and is complicated by the extreme structural diversity of the five antifreeze types. Despite the recent acquisition of several AFP three-dimensional structures and the definition of their ice-binding sites by mutagenesis, no common ice-binding motif or even theme is apparent except that surface-surface complementarity is important for binding. The remarkable diversity of antifreeze types and their seemingly haphazard phylogenetic distribution suggest that these proteins might have evolved recently in response to sea level glaciation occurring just 1-2 million years ago in the northern hemisphere and 10-30 million years ago around Antarctica. Not surprisingly, the expression of AFP genes from different origins can also be quite dissimilar. The most intensively studied system is that of the winter flounder, which has a built-in annual cycle of antifreeze expression controlled by growth hormone (GH) release from the pituitary in tune with seasonal cues. The signal transduction pathway, transcription factors, and promoter elements involved in this process are just beginning to be characterized.

Thermal hysteresis proteins

Extreme environments present a wealth of biochemical adaptations. Thermal hysteresis proteins (THPs) have been found in vertebrates, invertebrates, plants, bacteria and fungi and are able to depress the freezing point of water (in the presence of ice crystals) in a non-colligative manner by binding to the surface of nascent ice crystals. The THPs comprise a disparate group of proteins with a variety of tertiary structures and often no common sequence similarities or structural motifs. Different THPs bind to different faces of the ice crystal, and no single mechanism has been proposed to account for THP ice binding affinity and specificity. Experimentally THPs have been used in the cryopreservation of tissues and cells and to induce cold tolerance in freeze susceptible organisms. THPs represent a remarkable example of parallel and convergent evolution with different proteins being adapted for an anti-freeze role.

Temperature-dependent expression of cytochrome-c oxidase in Antarctic and temperate fish

Seasonal acclimation versus permanent adaptation to low temperatures leads to a differential response in the expression of cytochrome-c oxidase (CCO) in temperate and Antarctic eelpouts. Although eurythermal eelpout from the North Sea (Zoarces viviparus) displayed a cold-induced rise of CCO activity in white muscle, enzyme activity in the cold stenothermal Antarctic eelpout Pachycara brachycephalum failed to reflect such a compensatory increase. In Antarctic eelpout, CCO activity correlates with transcript levels of mitochondrial encoded subunits of CCO (CCO I and CCO II), whereas cold-acclimated eelpout from the North Sea show lower enzyme activities than expected on the basis of mitochondrial mRNA levels. In these animals, CCO expression at low temperatures may be limited either by nuclear CCO transcripts or by posttranscriptional processes. These may comprise translation of the subunits or assembly of the CCO holoenzyme. mRNA levels of CCO IV, one of the nuclear encoded subunits, increased strongly during cold acclimation, indicating that the expression of CCO is likely not message limited in cold-acclimated Z. viviparus. Our data suggest that seasonal cold acclimation of Z. viviparus results in a modification of the relationship between transcription and translation or posttranslational processes. In permanently cold-adapted P. brachycephalum, on the other hand, CCO expression shows similar characteristics as in the warm-acclimated confamilial species, e.g., low levels of enzyme activity correlated with low levels of mitochondrial message.

Type II fish antifreeze protein accumulation in transgenic tobacco does not confer frost resistance

Type II fish antifreeze protein (AFP) is active in both freezing point depression and the inhibition of ice recrystallization. This extensively disulfide-bonded 14 kDa protein was targeted for accumulation in its pro- and mature forms in the cytosol and apoplast of transgenic tobacco plants. Type II AFP gene constructs under control of a duplicate cauliflower mosaic virus 35S promoter, both with and without a native plant transit peptide sequence, were introduced into tobacco by Agrobacterium tumefaciens-mediated transformation. AFP did not accumulate in the cytosol of transgenic plants, but active AFP was present as 2% the total protein present in the apoplast. Plant-produced AFP was the same size as mature Type II AFP isolated from fish, and was comparable to wild-type AFP in thermal hysteresis activity and its effect on ice crystal morphology. Field trials conducted in late summer on R1 generation transgenic plants showed similar AFP accumulation in plants under field conditions at levels suitable for large-scale production: but no difference in frost resistance was observed between transgenic and wild-type plants during the onset of early fall frosts.