A cold-adapted esterase of a novel marine isolate, Pseudoalteromonas arctica: gene cloning, enzyme purification and characterization

A gene encoding an esterase (estO) was identified and sequenced from a gene library screen of the psychrotolerant bacterium Pseudoalteromonas arctica. Analysis of the 1,203 bp coding region revealed that the deduced peptide sequence is composed of 400 amino acids with a predicted molecular mass of 44.1 kDa. EstO contains a N-terminal esterase domain and an additional OsmC domain at the C-terminus (osmotically induced family of proteins). The highly conserved five-residue motif typical for all α/β hydrolases (G × S × G) was detected from position 104 to 108 together with a putative catalytic triad consisting of Ser¹⁰⁶, Asp¹⁹⁶, and His²²⁵. Sequence comparison showed that EstO exhibits 90% amino acid identity with hypothetical proteins containing similar esterase and OsmC domains but only around 10% identity to the amino acid sequences of known esterases. EstO variants with and without the OsmC domain were produced and purified as His-tag fusion proteins in E. coli. EstO displayed an optimum pH of 7.5 and optimum temperature of 25°C with more than 50% retained activity at the freezing point of water. The thermostability of EstO (50% activity after 5 h at 40°C) dramatically increased in the truncated variant (50% activity after 2.5 h at 90°C). Furthermore, the esterase displays broad substrate specificity for esters of short-chain fatty acids (C₂–C₈).     

Effect of 3D-scaffold formation on differentiation and survival in human neural progenitor cells

Background  

3D-scaffolds have been shown to direct cell growth and differentiation in many different cell types, with the formation and functionalisation of the 3D-microenvironment being important in determining the fate of the embedded cells. Here we used a hydrogel-based scaffold to investigate the influences of matrix concentration and functionalisation with laminin on the formation of the scaffolds, and the effect of these scaffolds on human neural progenitor cells cultured within them.     

Angiopoietin-2 Stimulation of Endothelial Cells Induces αvβ3 Integrin Internalization and Degradation

The angiopoietins (Ang-1 and Ang-2) have been identified as agonistic and antagonistic ligands of the endothelial receptor tyrosine kinase Tie2, respectively. Both ligands have been demonstrated to induce translocation of Tie2 to cell-cell junctions. However, only Ang-1 induces Tie2-dependent Akt activation and subsequent survival signaling and endothelial quiescence. Ang-2 interferes negatively with Ang-1/Tie2 signaling, thereby antagonizing the Ang-1/Tie2 axis. Here, we show that both Ang-1 and Ang-2 recruit β3 integrins to Tie2. This co-localization is most prominent in cell-cell junctions. However, only Ang-2 stimulation resulted in complex formation among Tie2, αvβ3 integrin, and focal adhesion kinase as evidenced by co-immunoprecipitation experiments. Focal adhesion kinase was phosphorylated in the FAT domain at Ser⁹¹⁰ upon Ang-2 stimulation and the adaptor proteins p130Cas and talin dissociated from αvβ3 integrin. The αvβ3 integrin was internalized, ubiquitinylated, and gated toward lysosomes. Taken together, the experiments define Tie2/αvβ3 integrin association-induced integrin internalization and degradation as mechanistic consequences of endothelial Ang-2 stimulation.     

Functional Hybrid Rubisco Enzymes with Plant Small Subunits and Algal Large Subunits: ENGINEERED rbcS cDNA FOR EXPRESSION IN CHLAMYDOMONAS*?

There has been much interest in the chloroplast-encoded large subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) as a target for engineering an increase in net CO₂ fixation in photosynthesis. Improvements in the enzyme would lead to an increase in the production of food, fiber, and renewable energy. Although the large subunit contains the active site, a family of rbcS nuclear genes encodes the Rubisco small subunits, which can also influence the carboxylation catalytic efficiency and CO₂/O₂ specificity of the enzyme. To further define the role of the small subunit in Rubisco function, small subunits from spinach, Arabidopsis, and sunflower were assembled with algal large subunits by transformation of a Chlamydomonas reinhardtii mutant that lacks the rbcS gene family. Foreign rbcS cDNAs were successfully expressed in Chlamydomonas by fusing them to a Chlamydomonas rbcS transit peptide sequence engineered to contain rbcS introns. Although plant Rubisco generally has greater CO₂/O₂ specificity but a lower carboxylation V_max than Chlamydomonas Rubisco, the hybrid enzymes have 3–11% increases in CO₂/O₂ specificity and retain near normal V_max values. Thus, small subunits may make a significant contribution to the overall catalytic performance of Rubisco. Despite having normal amounts of catalytically proficient Rubisco, the hybrid mutant strains display reduced levels of photosynthetic growth and lack chloroplast pyrenoids. It appears that small subunits contain the structural elements responsible for targeting Rubisco to the algal pyrenoid, which is the site where CO₂ is concentrated for optimal photosynthesis.     

CXCR7 protein is not expressed on human or mouse leukocytes

Since the discovery that CXCR7 binds to CXCL12/SDF-1α, the role of CXCR7 in CXCL12-mediated biological processes has been under intensive scrutiny. However, there is no consensus in the literature on the expression of CXCR7 protein by peripheral blood cells. In this study we analyzed human and mouse leukocytes and erythrocytes for CXCR7 protein expression, using a competitive CXCL12 binding assay as well as by flow cytometry and immunohistochemistry using multiple CXCR7 Abs. CXCR7(-/-) mice were used as negative controls. Together, these methods indicate that CXCR7 protein is not expressed by human peripheral blood T cells, B cells, NK cells, or monocytes, or by mouse peripheral blood leukocytes. CXCR7 protein is, however, expressed on mouse primitive erythroid cells, which supply oxygen to the embryo during early stages of development. These studies therefore suggest that, whereas CXCR7 protein is expressed by primitive RBCs during murine embryonic development, in adult mammals CXCR7 protein is not expressed by normal peripheral blood cells.     

Non‐viral VEGF165 gene therapy – magnetofection of acoustically active magnetic lipospheres (‘magnetobubbles’) increases tissue survival in an oversized skin flap model

Adenoviral transduction of the VEGF gene in an oversized skin flap increases flap survival and perfusion. In this study, we investigated the potential of magnetofection of magnetic lipospheres containing VEGF₁₆₅‐cDNA on survival and perfusion of ischemic skin flaps and evaluated the method with respect to the significance of applied magnetic field and ultrasound. We prepared perfluoropropane‐filled magnetic lipospheres (‘magnetobubbles’) from Tween60‐coated magnetic nanoparticles, Metafectene, soybean‐oil and cDNA and studied the effect in an oversized random‐pattern‐flap model in the rats (n= 46). VEGF‐cDNA‐magnetobubbles were administered under a magnetic field with simultaneously applied ultrasound, under magnetic field alone and with applied ultrasound alone. Therapy was conducted 7 days pre‐operative. Flap survival and necrosis were measured 7 days post‐operatively. Flap perfusion, VEGF‐protein concentration in target and surrounding tissue, formation and appearance of new vessels were analysed additionally. Magnetofection with VEGF‐cDNA‐magnetobubbles presented an increased flap survival of 50% and increased flap perfusion (P < 0.05). Without ultrasound and without magnetic field, the effect is weakened. VEGF concentration in target tissue was elevated (P < 0.05), while underlying muscle was not affected. Our results demonstrate the successful VEGF gene therapy by means of magnetobubble magnetofection. Here, the method of magnetofection of magnetic lipospheres is equally efficient as adenoviral transduction, but has a presumable superior safety profile.     

Cdc5 blocks in vivo rad53 activity,but not in situ activity (ISA)

DNA damage promotes the activation of a signal transduction cascade referred to as the DNA damage checkpoint. This pathway initiates with the Mec1/ATR kinase, which then phosphorylates the Rad53/Chk2 kinase. Mec1 phosphorylation of Rad53 is then thought to promote Rad53 autophosphorylation, ultimately leading to a fully active Rad53 molecule that can go on to phosphorylate substrates important for DNA damage resistance. In the absence of DNA repair, this checkpoint is eventually downregulated in a Cdc5-dependent process referred to as checkpoint adaptation. Recently, we showed that overexpression of Cdc5 leads to checkpoint inactivation and loss of the strong electrophoretic shift associated with Rad53 inactivation. Interestingly, this same overexpression did not strongly inhibit Rad53 autophosphorylation activity as measured by the in situ assay (ISA). The ISA involves incubating the re-natured Rad53 protein with γ ³²P labeled ATP after electrophoresis and western blotting. Using a newly identified Rad53 target, we show that despite strong ISA activity, Rad53 does not maintain phosphorylation of this substrate. We hypothesize that, during adaptation, Rad53 may be in a unique state in which it maintains some Mec1 phosphorylation but does not have the auto-phosphorylations required for full activity towards exogenous substrates.Key words: DNA damage, checkpoint, adaptation, CDC5, RAD53, ISA     

Association of Early Repolarization Pattern on ECG with Risk of Cardiac and All-Cause Mortality: A Population-Based Prospective Cohort Study (MONICA/KORA)

Background

Early repolarization pattern (ERP) on electrocardiogram was associated with idiopathic ventricular fibrillation and sudden cardiac arrest in a case-control study and with cardiovascular mortality in a Finnish community-based sample. We sought to determine ERP prevalence and its association with cardiac and all-cause mortality in a large, prospective, population-based case-cohort study (Monitoring of Cardiovascular Diseases and Conditions [MONICA]/KORA [Cooperative Health Research in the Region of Augsburg]) comprised of individuals of Central-European descent.

Methods and Findings

Electrocardiograms of 1,945 participants aged 35–74 y, representing a source population of 6,213 individuals, were analyzed applying a case-cohort design. Mean follow-up was 18.9 y. Cause of death was ascertained by the 9th revision of the International Classification of Disease (ICD-9) codes as documented in death certificates. ERP-attributable effects on mortality were determined by a weighted Cox proportional hazard model adjusted for covariables. Prevalence of ERP was 13.1% in our study. ERP was associated with cardiac and all-cause mortality, most pronounced in those of younger age and male sex; a clear ERP-age interaction was detected (p = 0.005). Age-stratified analyses showed hazard ratios (HRs) for cardiac mortality of 1.96 (95% confidence interval [CI] 1.05–3.68, p = 0.035) for both sexes and 2.65 (95% CI 1.21–5.83, p = 0.015) for men between 35–54 y. An inferior localization of ERP further increased ERP-attributable cardiac mortality to HRs of 3.15 (95% CI 1.58–6.28, p = 0.001) for both sexes and to 4.27 (95% CI 1.90–9.61, p<0.001) for men between 35–54 y. HRs for all-cause mortality were weaker but reached significance.

Conclusions

We found a high prevalence of ERP in our population-based cohort of middle-aged individuals. ERP was associated with about a 2- to 4-fold increased risk of cardiac mortality in individuals between 35 and 54 y. An inferior localization of ERP was associated with a particularly increased risk. Please see later in the article for the Editors'' Summary     

Antiangiogenic activity of 2-deoxy-D-glucose

Background

During tumor angiogenesis, endothelial cells (ECs) are engaged in a number of energy consuming biological processes, such as proliferation, migration, and capillary formation. Since glucose uptake and metabolism are increased to meet this energy need, the effects of the glycolytic inhibitor 2-deoxy-D-glucose (2-DG) on in vitro and in vivo angiogenesis were investigated.

Methodology/Principal Findings

In cell culture, 2-DG inhibited EC growth, induced cytotoxicity, blocked migration, and inhibited actively forming but not established endothelial capillaries. Surprisingly, 2-DG was a better inhibitor of these EC properties than two more efficacious glycolytic inhibitors, 2-fluorodeoxy-D-glucose and oxamate. As an alternative to a glycolytic inhibitory mechanism, we considered 2-DG''s ability to interfere with endothelial N-linked glycosylation. 2-DG''s effects were reversed by mannose, an N-linked glycosylation precursor, and at relevant concentrations 2-DG also inhibited synthesis of the lipid linked oligosaccharide (LLO) N-glycosylation donor in a mannose-reversible manner. Inhibition of LLO synthesis activated the unfolded protein response (UPR), which resulted in induction of GADD153/CHOP and EC apoptosis (TUNEL assay). Thus, 2-DG''s effects on ECs appeared primarily due to inhibition of LLOs synthesis, not glycolysis. 2-DG was then evaluated in two mouse models, inhibiting angiogenesis in both the matrigel plug assay and the LH_BETAT_AG transgenic retinoblastoma model.

Conclusions/Significance

In conclusion, 2-DG inhibits endothelial cell angiogenesis in vitro and in vivo, at concentrations below those affecting tumor cells directly, most likely by interfering with N-linked glycosylation rather than glycolysis. Our data underscore the importance of glucose metabolism on neovascularization, and demonstrate a novel approach for anti-angiogenic strategies.