Structural determinants of cold adaptation and stability in a large protein

The heat-labile alpha-amylase from an antarctic bacterium is the largest known protein that unfolds reversibly according to a two-state transition as shown by differential scanning calorimetry. Mutants of this enzyme were produced, carrying additional weak interactions found in thermostable alpha-amylases. It is shown that single amino acid side chain substitutions can significantly modify the melting point T(m), the calorimetric enthalpy Delta H(cal), the cooperativity and reversibility of unfolding, the thermal inactivation rate constant, and the kinetic parameters k(cat) and K(m). The correlation between thermal inactivation and unfolding reversibility displayed by the mutants also shows that stabilizing interactions increase the frequency of side reactions during refolding, leading to intramolecular mismatches or aggregations typical of large proteins. Although all mutations were located far from the active site, their overall trend is to decrease both k(cat) and K(m) by rigidifying the molecule and to protect mutants against thermal inactivation. The effects of these mutations indicate that the cold-adapted alpha-amylase has lost a large number of weak interactions during evolution to reach the required conformational plasticity for catalysis at low temperatures, thereby producing an enzyme close to the lowest stability allowing maintenance of the native conformation.     

Heat shock protein of Hsp70 in Paramecium nephridiatum and its role in adaptation to environmental salinity changes

The level of Hsp70 was studied in the cells of eurihaline ciliate Paramecium nephridiatum after the environmental salinity changes. Two types of treatment were applied. "Shock": ciliates were placed for 1 h to the medium with stress salinity, then transferred back to the medium, they were acclimated to, for 2 h; "adaptation": ciliates were placed for 3 h into stress salinity. It has been shown, that ciliates, acclimated to fresh water (0%) have the higher constitutive level of Hsp70, than those, acclimated to 10%. Transfer from fresh water to 10% does not cause the increase of Hsp70 synthesis in protists, whereas the reciprocal transfer results in induction of Hsp70 in the cells. "Adaptation" results in induction of Hsp70 in both "directions" of salinity changes. The results obtained allow to presume that the possibility to survive in the media of various salinity in eurihaline ciliates is somehow determined by the higher initial level of Hsp70 in their cells, than in stenohaline representatives of the same genus.     

Physiological mechanisms of frost tolerance: Possible role of protein in plant adaptation to cold

Studies performed on winter rape plants(Brassica nnpus var.oleifera, cv. ‘Gór-czański’) revealed that cold treatment affected the cell membranes and led to the temporary increase in electrolytic leakage from a tissue. This was followed by the marked decrease of the electrolytic leakage in the course of hardening. Changes in membrane properties were accompanied by the promotion of soluble protein accumulation. Inhibition of protein accumulation by the cycloheximide treatment brought about wilting of plants under cold conditions. Possible role of soluble protein in protection of cells against secondary water stress caused by the coldinduced changes in membrane properties is suggested. Cold-induced changes in the electrophoretic pattern of soluble protein are described and discussed.     

Caenorhabditis elegans auxilin: a J-domain protein essential for clathrin-mediated endocytosis in vivo

The budding of clathrin-coated vesicles is essential for protein transport. After budding, clathrin must be uncoated before the vesicles can fuse with other membranous structures. In vitro, the molecular chaperone Hsc70 uncoats clathrin-coated vesicles in an ATP-dependent process that requires a specific J-domain protein such as auxilin. However, there is little evidence that either Hsc70 or auxilin is essential in vivo. Here we show that C. elegans has a single auxilin homologue that is identical to mammalian auxilin in its in vitro activity. When RNA-mediated interference (RNAi) is used to inhibit auxilin expression in C. elegans, oocytes show markedly reduced receptor-mediated endocytosis of yolk protein tagged with green fluorescent protein (GFP). In addition, most of these worms arrest during larval development, exhibit defective distribution of GFP-clathrin in many cell types, and show a marked change in clathrin dynamics, as determined by fluorescence recovery after photobleaching (FRAP). We conclude that auxilin is required for in vivo clathrin-mediated endocytosis and development in C. elegans.     

Purine stress in crithidia: adaptation of a parasite to environmental stress

How parasitic protozoa survive varying nutrient levels is a key issue in parasitology. Here, Annette Gero explains how the Trypanosomatid Crithidia luciliae responds to purine stress by increasing the rates of transport of nucleosides and bases from the environment and by increasing the activity of the ectoenzyme 3'-nucleotidase (3'NTase), which breaks down external nucleotides so that they can be salvaged as nucleosides. The increase in activity of the purine transporters, and the 3'NTase activity is simultaneous with a general increase in the purine metabolic pathway, hence ensuring that purines are readily available to the parasite during purine stress.     

Conservation information: a market incentive to promote environmental quality

The land market in part of New South Wales, Australia, has been shown to conserve the soil and promote sustainable agriculture. The market incentive at work is the availability of information on the erosion status of the land. This paper explores the general possibility that provision of market information on environmental characteristics will lead to improvements in environmental quality. In this way the market would encourage landowners to conserve their land, retain native vegetation, improve biodiversity and pursue sustainable agriculture. They would do all this automatically, without government regulations, bans or moratoria, and without a new government agency or new act to implement the policy. The government officers would merely show buyers and sellers in the land market where to obtain, and how to use, the relevant information.     

Temperature-responsive release of thyroxine and its environmental adaptation in Australians

The hormone thyroxine that regulates mammalian metabolism is carried and stored in the blood by thyroxine-binding globulin (TBG). We demonstrate here that the release of thyroxine from TBG occurs by a temperature-sensitive mechanism and show how this will provide a homoeostatic adjustment of the concentration of thyroxine to match metabolic needs, as with the hypothermia and torpor of small animals. In humans, a rise in temperature, as in infections, will trigger an accelerated release of thyroxine, resulting in a predictable 23% increase in the concentration of free thyroxine at 39°C. The in vivo relevance of this fever-response is affirmed in an environmental adaptation in aboriginal Australians. We show how two mutations incorporated in their TBG interact in a way that will halve the surge in thyroxine release, and hence the boost in metabolic rate that would otherwise occur as body temperatures exceed 37°C. The overall findings open insights into physiological changes that accompany variations in body temperature, as notably in fevers.     

Physical and molecular bases of protein thermal stability and cold adaptation

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A cellular J-domain protein modulates polyprotein processing and cytopathogenicity of a pestivirus

Pestiviruses are positive-strand RNA viruses closely related to human hepatitis C virus. Gene expression of these viruses occurs via translation of a polyprotein, which is further processed by cellular and viral proteases. Here we report the formation of a stable complex between an as-yet-undescribed cellular J-domain protein, a member of the DnaJ-chaperone family, and pestiviral nonstructural protein NS2. Accordingly, we termed the cellular protein Jiv, for J-domain protein interacting with viral protein. Jiv has the potential to induce in trans one specific processing step in the viral polyprotein, namely, cleavage of NS2-3. Efficient generation of its cleavage product NS3 has previously been shown to be obligatory for the cytopathogenicity of the pestiviruses. Regulated expression of Jiv in cells infected with noncytopathogenic bovine viral diarrhea virus disclosed a direct correlation between the intracellular level of Jiv, the extent of NS2-3 cleavage, and pestiviral cytopathogenicity.     

Fueguian cranial morphology: The adaptation to a cold,harsh environment

Craniometric data from the three extinct tribes that inhabited Tierra del Fuego (Selk'nam, Yámana, and Kawéskar) were gathered following Howells's measurement technique. We studied 180 skulls preserved at thirteen different institutions. Analysis of variance (ANOVA) between groups showed that morphological similarities among Fueguian groups are far more important than some differences between marine (Yámana and Kawéskar) and terrestrial (Selk'nam) groups. A principal component analysis (PCA) generated from the correlation matrix shows that Fueguians fall as outliers with respect to the typical Mongoloid morphology. In addition, a UPGMA tree generated from a squared Euclidean distance matrix indicates that Fueguian groups have a morphological pattern that is very distinct from that of other present-day Amerindian groups, with the exception of the Eskimos. One of the variables that contributes substantially to the differentiation of Eskimos and Fueguians is the nasal height. This suggests that nasal morphology in both groups could be a response to adaptive pressures related to the cold environment. However, other morphological particularities of Fueguian skulls, such as craniofacial robustness and variables of craniofacial width, can be attributed to a large masticatory stress. As a whole, the morphological features of Fueguian groups can be regarded as a general adaptive response to a very harsh environment, along with the retention of some plesiomorphic features. Assuming that the initial entry in Tierra de Fuego took place around 10,000 years BP, before the disappearance of the last land bridges in the Magellan Straits, then this adaptation might have arisen in a relatively short period, hastened by the extreme environmental conditions. Am J Phys Anthropol 103:103–117, 1997. © 1997 Wiley-Liss, Inc.     

Cytokinins: metabolism and function in plant adaptation to environmental stresses

In plants, the cytokinin (CK) phytohormones regulate numerous biological processes, including responses to environmental stresses, via a complex network of CK signaling. By an unknown mechanism, stress signals are perceived and transmitted through the His-Asp phosphorelay, an important component of the CK signal transduction pathway, triggering CK-responsive genes. Because of the intensive crosstalk between CKs and abscisic acid (ABA), modulation of CK levels and their signal transduction affects both ABA-dependent and ABA-independent pathways, enabling plant adaptation to adverse conditions. This review presents our current understanding of the functions of CKs and CK signaling in the regulation of plant adaptation to stress. Biotechnological strategies based on the modulation of CK levels have been examined with the aim of stabilizing agriculture yields.     

Vivipary in Polygonum viviparum: an adaptation to cold climate?

Populations of Polygonurn viviparurn were investigated in the Swiss Alps at 14 sites, ranging from 450 m to 2530 m above sea level. The average length of stems and the mean number of reproductive organs (flowers + bulbils) decreased significantly with increasing altitude. On average, the ratio of flowers to bulbils per inflorescence also declined so that at high altitudes, bulbil production was more pronounced. Increased allocation to vegetative reproduction is discussed as an adaptation to cold climate. It is suggested that enhanced vegetative reproduction might be controlled by incornplete floral induction in high altitudes. In addition variability within and between populations was investigated by isozyme electrophoresis and the examination of bulbil colours. A considerable amount of variability was found in alpine populations. The demonstrated genetic variability showed that in P. viviparum it is likely that minor sexual reproduction is maintained even under alpine conditions. This is reflected in different enzyme phenotypes and different bulbil colours.     

细菌产黄素类化合物介导的电子传递及对环境污染物的厌氧生物转化研究进展

氧化还原介体能够加速有毒环境污染物的厌氧生物转化。黄素类化合物是一类微生物自身合成分泌的氧化还原介体,其应用可有效地避免外源性介体带来的成本较高及造成二次污染的问题,因此引起了广泛的关注。研究表明,细菌合成的微量黄素类化合物不仅能够作为黄素蛋白的辅酶因子参与偶氮染料、铬酸盐和硝基芳烃等污染物的厌氧生物转化,并且还可以分泌到胞外将电子传递给固态电子受体如含铁矿物和电极等来参与生物修复过程。根据黄素类化合物的功能,本文综述了黄素类化合物的合成与分泌,及其介导的胞内外电子传递和对环境污染物厌氧生物转化的影响,以促进其在实际环境污染物处理中的应用。