Adaptation to thermally variable environments: capacity for acclimation of thermal limit and heat shock response in the shrimp Palaemonetes varians

In the context of climate change, there is a sustained interest in understanding better the functional mechanisms by which marine ectotherms maintain their physiological scope and define their ability to cope with thermal changes in their environment. Here, we present evidence that the variable shrimp Palaemonetes varians shows genuine acclimation capacities of both the thermal limit (CT(max)) and the heat shock response (hsp70 induction temperature). During cold acclimation to 10?°C, the time lag to adjust the stress gene expression to the current environmental temperature proved to exceed 1?week, thereby highlighting the importance of long-term experiments in evaluating the species' acclimation capacities. Cold and warm-acclimated specimens of P. varians can mobilise the heat shock response (HSR) at temperatures above those experienced in nature, which suggests that the species is potentially capable of expanding its upper thermal range. The shrimp also survived acute heat shock well above its thermal limit without subsequent induction of the HSR, which is discussed with regard to thermal adaptations required for life in highly variable environments.     

Bilirubin oxidase from Magnaporthe oryzae: an attractive new enzyme for biotechnological applications

A novel bilirubin oxidase (BOD), from the rice blast fungus Magnaporthe oryzae, has been identified and isolated. The 64-kDa protein containing four coppers was successfully overexpressed in Pichia pastoris and purified to homogeneity in one step. Protein yield is more than 100?mg for 2?L culture, twice that of Myrothecium verrucaria. The k _cat/K _m ratio for conjugated bilirubin (1,513?mM^?1?s^?1) is higher than that obtained for the BOD from M. verrucaria expressed in native fungus (980?mM^?1?s^?1), with the lowest K _m measured for any BOD highly desirable for detection of bilirubin in medical samples. In addition, this protein exhibits a half-life for deactivation >300?min at 37?°C, high stability at pH?7, and high tolerance towards urea, making it an ideal candidate for the elaboration of biofuel cells, powering implantable medical devices. Finally, this new BOD is efficient in decolorizing textile dyes such as Remazol brilliant Blue R, making it useful for environmentally friendly industrial applications.     

Catalytic residues and a predicted structure of tetrahydrobiopterin-dependent alkylglycerol mono-oxygenase

Alkylglycerol mono-oxygenase (EC 1.14.16.5) forms a third, distinct, class among tetrahydrobiopterin-dependent enzymes in addition to aromatic amino acid hydroxylases and nitric oxide synthases. Its protein sequence contains the fatty acid hydroxylase motif, a signature indicative of a di-iron centre, which contains eight conserved histidine residues. Membrane enzymes containing this motif, including alkylglycerol mono-oxygenase, are especially labile and so far have not been purified to homogeneity in active form. To obtain a first insight into structure-function relationships of this enzyme, we performed site-directed mutagenesis of 26 selected amino acid residues and expressed wild-type and mutant proteins containing a C-terminal Myc tag together with fatty aldehyde dehydrogenase in Chinese-hamster ovary cells. Among all of the acidic residues within the eight-histidine motif, only mutation of Glu137 to alanine led to an 18-fold increase in the Michaelis-Menten constant for tetrahydrobiopterin, suggesting a role in tetrahydrobiopterin interaction. A ninth additional histidine residue essential for activity was also identified. Nine membrane domains were predicted by four programs: ESKW, TMHMM, MEMSAT and Phobius. Prediction of a part of the structure using the Rosetta membrane ab initio method led to a plausible suggestion for a structure of the catalytic site of alkylglycerol mono-oxygenase.     

Cycloheximide as a tool to investigate protein import in peroxisomes: a case study of the subcellular localization of isoprenoid biosynthetic enzymes

Cytosolic background fluorescence is often observed when native low-abundance peroxisomal proteins carrying a weak peroxisomal targeting sequence are expressed as fluorescent fusion protein using a strong constitutive promoter in transiently transformed plant cells. This cytosolic fluorescence usually comes from the strong expression of the low-abundance proteins exceeding the peroxisome import efficiency. This often results in a misinterpretation of the protein subcellular localization, as there is doubt as to whether proteins are dually targeted to the cytosol and peroxisome or are exclusively localized to peroxisomes. To circumvent this experimental difficulty, the protein peroxisome import study can be optimized by de novo protein synthesis inhibition in transiently transformed cells using the translation inhibitor cycloheximide. This approach was used here successfully for the study of the subcellular localization of distinct plant isoprenoid biosynthetic enzymes, allowing us to clearly demonstrate that 5-phosphomevalonate kinase, mevalonate 5-diphosphate decarboxylase and a short isoform of farnesyl diphosphate synthase from Catharanthus roseus are exclusively localized to peroxisomes.     

Kruppel-like factor 1 (KLF1), KLF2, and Myc control a regulatory network essential for embryonic erythropoiesis

The Krüppel-like factor 1 (KLF1) and KLF2 positively regulate embryonic β-globin expression and have additional overlapping roles in embryonic (primitive) erythropoiesis. KLF1(-/-) KLF2(-/-) double knockout mice are anemic at embryonic day 10.5 (E10.5) and die by E11.5, in contrast to single knockouts. To investigate the combined roles of KLF1 and KLF2 in primitive erythropoiesis, expression profiling of E9.5 erythroid cells was performed. A limited number of genes had a significantly decreasing trend of expression in wild-type, KLF1(-/-), and KLF1(-/-) KLF2(-/-) mice. Among these, the gene for Myc (c-Myc) emerged as a central node in the most significant gene network. The expression of the Myc gene is synergistically regulated by KLF1 and KLF2, and both factors bind the Myc promoters. To characterize the role of Myc in primitive erythropoiesis, ablation was performed specifically in mouse embryonic proerythroblast cells. After E9.5, these embryos exhibit an arrest in the normal expansion of circulating red cells and develop anemia, analogous to KLF1(-/-) KLF2(-/-) embryos. In the absence of Myc, circulating erythroid cells do not show the normal increase in α- and β-like globin gene expression but, interestingly, have accelerated erythroid cell maturation between E9.5 and E11.5. This study reveals a novel regulatory network by which KLF1 and KLF2 regulate Myc to control the primitive erythropoietic program.     

Randomness + determinism = progresses: Why random processes could be favored by evolution

Biologists are somehow pioneers on the idea that progress can be driven by randomness: randomness is one of the main engine of evolution; small variations induced by randomness coupled with natural selection allows the species to self-adapt to their moving environment. Studies from the last 40 years in computer science suggest that randomness is in fact able of doing much more and revealed unexpected possibilities which might appear impossible at first. Furthermore, it turns out that these discoveries are faster, cheaper and above all exponentially thriftier than their deterministic alternatives. This means that random explorations would almost surely generate a stochastic process way before any equivalent deterministic counterpart is found. It follows that most likely these processes are favored by evolution and should thus be known to anyone dealing with systems (alive or not) having access to random sources. This article presents some of these counter-intuitive results as a possible source of inspiration for studying systems fed with randomness.     

Co-expression of the small heat shock protein, Lo18, with β-glucosidase in Escherichia coli improves solubilization and reveals various associations with overproduced heterologous protein, GroEL/ES

We developed a new system to improve the overproduction of soluble proteins in E. coli based on a plasmid encoding the small heat-shock protein, Lo18, derived from the lactic acid bacterium Oenococcus oeni. The efficiency of this system was compared with that of another system based on production of the E. coli universal chaperone GroEL/ES. A compatible plasmid encoding β-glucosidase was constructed for the overproduction and aggregation of this enzyme. Co-expression with Lo18 resulted in an increase in soluble β-glucosidase levels similar to that obtained in the GroEL/ES co-expression system. Lo18 was found preferentially in the insoluble fraction, associated with aggregated enzyme. By contrast, GroEL/ES was more abundant in the soluble fraction.