Inverse metabolic engineering with phosphagen kinase systems improves the cellular energy state

Inverse metabolic engineering attempts to identify or construct desired phenotypes of applied interest to endow them on appropriate host organisms. A particular desirable phenotype is the ATP homeostasis exhibited by animal cells with high and variable ATP turnover through temporal and spatial energy buffering. This buffering is achieved by phosphagen kinase systems that consist of a specific kinase and its cognate phosphagen, which functions as a large pool of 'high-energy phosphates' that are used to replenish ATP during periods of high energetic demand. This review discusses recent advances and potentials of inverse metabolic engineering of cell types that do not normally contain such systems--bacteria, yeast, plants, and liver--with creatine or arginine kinase systems. Examples are discussed that illustrate how microbial metabolism can be tailored for large-scale industrial processes with imperfect mixing and how the liver can be protected from metabolic insults or stimulated for better regeneration.     

A functionally improved locked nucleic acid antisense oligonucleotide inhibits Bcl-2 and Bcl-xL expression and facilitates tumor cell apoptosis

We previously reported the Bcl-2/Bcl-xL-bispecific activity of the 2'-O-(2-methoxy)ethyl (2'-MOE)-modified gapmer antisense oligonucleotide 4625. This oligonucleotide has 100% complementarity to Bcl-2 and three mismatches to Bcl-xL. In the present study, the isosequential locked nucleic acid (LNA)-modified oligonucleotide 5005 was generated, and its ability to further improve the downregulation of the two antiapoptotic targets in tumor cells was examined. We demonstrate that compared with 4625, 5005 more effectively decreased the expression of the mismatching Bcl-xL target gene in MDA-MB-231 breast and H125 lung cancer cells. In both cell lines, antisense activity caused decreased cell viability by induction of apoptosis. Moreover, in combination with various anticancer agents, 5005 reduced tumor cell viability more effectively than 4625. We describe for the first time the functional comparison of isosequential Bcl-2/Bcl-xL-bispecific 2'-MOE and LNA-modified antisense oligonucleotides and report that the LNA analog more effectively downregulated the two apoptosis inhibitors overexpressed in human tumors. Our data underscore the ability of LNA modifications to enhance the efficacy and favorably modulate the target specificity of antisense oligonucleotides.     

The use of antlers to monitor temporal variation in environmental lead levels: a case study from an industrialized area in Germany

In order to assess temporal changes in ambient lead levels, Pb concentrations were determined in roe deer (Capreolus capreolus) antlers (n=116) that had been collected in the industrialized area of Siegen (western Germany) in the period 1948–2000. Lead concentrations ranged between 0.3 and 166.3 mg/kg dry weight. An overall decline in antler Pb concentration occurred from the mid-1970s onward, and lead concentrations in the samples from the periods 1980–1989 and 1990–2000 were significantly lower than those in samples from previous periods. Our findings indicate a marked decline in lead exposure of the roe deer inhabiting the study area in the recent past. This decline is attributed to a decrease in atmospheric lead deposition, caused mainly by the phase-out of leaded gasoline, and, in addition, by a reduction of lead emissions from stationary sources. The results of the present study and of previous investigations demonstrate that analysis of antler samples obtained in an area over a certain period can be used to reconstruct temporal changes in environmental lead levels.     

Malposition and loss of the left mandibular permanent canine in a male wild boar (<Emphasis Type="Italic">Sus scrofa</Emphasis> L.)

Few cases of pathological alterations of the continuously growing, rootless permanent canines (tusks) of male wild boars have been described in the scientific literature. In this paper we present a case of loss of the left mandibular permanent canine in a male wild boar from the Slovak Republic. The opening of the canines alveolus was misplaced posteriorly, which was evidence of a malposition of the tooth. The boars left maxillary tusk showed overgrowth and lacked a distinct wear surface, indicating that it had not been in contact with the left mandibular tusk due to the latters malposition. Our findings suggest that the left mandibular tusk had also shown overgrowth. It is supposed that malposition and overgrowth increased the tusks risk of being damaged, and that a strong mechanical impact caused a complete or incomplete fracture of the tooth. It is further supposed that infection and inflammation of the tusks pulp occurred as sequelae of the fracture. The spread of the infection and inflammation through the large opening at the tusks growing end then led to chronic osteomyelitis of the surrounding mandibular bone. In the course of the disease process, the tusk or its remnant was shed from the mandible.     

Comparison of the proteome of Methylobacterium extorquens AM1 grown under methylotrophic and nonmethylotrophic conditions

Methylobacterium extorquens AM1 is a facultative methylotrophic bacterium that is capable of growing in the presence of methanol as the sole carbon and energy source, but is also able to grow on a limited number of C(2), C(3), and C(4) compounds, for example succinate. This study provides a proteomic view of the cellular adaptation of M. extorquens AM1 to growth on methanol and succinate, respectively. Cytosolic proteins were separated by two-dimensional gel electrophoresis employing overlapping pH ranges and visualized by silver nitrate or fluorescence staining. A proteomic reference map containing 229 different proteins identified by peptide mass fingerprinting of tryptic fragments was established. Comparative proteome profiling of methanol- and succinate-grown cells led to the identification of 68 proteins that are induced under methylotrophic growth conditions in comparison to growth on succinate. This group includes most proteins known to be directly involved in methanol oxidation to CO(2) and in assimilation of one carbon units by the serine cycle as well as 18 proteins without any assigned function and two proteins with a predicted regulatory function. Furthermore, the proteome analysis revealed putative isoenzymes for formaldehyde-activating enzyme Fae, malyl-CoA lyase, malate-dehydrogenase, and fumarase, that need to be characterized functionally in future studies.     

Identification of PSF as a protein kinase Calpha-binding protein in the cell nucleus

Protein kinase C (PKC) isoforms are present in the cell nucleus in diverse cell lines and tissues. Since little is known about proteins interacting with PKC inside the cell nucleus, we used Neuro-2a neuroblastoma cells, in which PKCalpha is present in the nucleus, to screen for nuclear binding partners for PKC. Applying overlay assays, we detected several nuclear proteins which bind to PKCalpha. Specificity of binding was shown by its dependence on PKC activation by phorbol ester, calcium, and phosphatidylserine. The PKC-binding proteins were partially purified and analyzed by microsequencing and mass spectrometry. Four proteins could be identified: PTB-associated splicing factor (PSF), p68 RNA helicase, and the heterogeneous nuclear ribonucleoprotein (hnRNP) proteins A3 and L. In the case of PSF, binding to PKC could also be demonstrated in a GST-pull-down assay using GST-PKCalpha, expressed in insect cells. Phosphorylation experiments revealed that PSF is a weak in vitro substrate for PKCalpha.     

Comparative sequence analysis of the symbiosis island of Mesorhizobium loti strain R7A

The Mesorhizobium loti strain R7A symbiosis island is a 502-kb chromosomally integrated element which transfers to nonsymbiotic mesorhizobia in the environment, converting them to Lotus symbionts. It integrates into a phenylalanine tRNA gene in a process mediated by a P4-type integrase encoded at the left end of the element. We have determined the nucleotide sequence of the island and compared its deduced genetic complement with that reported for the 611-kb putative symbiosis island of M. loti strain MAFF303099. The two islands share 248 kb of DNA, with multiple deletions and insertions of up to 168 kb interrupting highly conserved colinear DNA regions in the two strains. The shared DNA regions contain all the genes likely to be required for Nod factor synthesis, nitrogen fixation, and island transfer. Transfer genes include a trb operon and a cluster of potential tra genes which are also present on the strain MAFF303099 plasmid pMLb. The island lacks plasmid replication genes, suggesting that it is a site-specific conjugative transposon. The R7A island encodes a type IV secretion system with strong similarity to the vir pilus from Agrobacterium tumefaciens that is deleted from MAFF303099, which in turn encodes a type III secretion system not found on the R7A island. The 414 genes on the R7A island also include putative regulatory genes, transport genes, and an array of metabolic genes. Most of the unique hypothetical genes on the R7A island are strain-specific and clustered, suggesting that they may represent other acquired genetic elements rather than symbiotically relevant DNA.     

Functional expression of phosphagen kinase systems confers resistance to transient stresses in Saccharomyces cerevisiae by buffering the ATP pool

Phosphagen kinase systems provide different advantages to tissues with high and fluctuating energy demands, in particular an efficient energy buffering system. In this study we show for the first time functional expression of two phosphagen kinase systems in Saccharomyces cerevisiae, which does not normally contain such systems. First, to establish the creatine kinase system, in addition to overexpressing creatine kinase isoenzymes, we had to install the biosynthesis pathway of creatine by co-overexpression of L-arginine:glycine amidinotransferase and guanidinoacetate methyltransferase. Although we could achieve considerable creatine kinase activity, together with more than 3 mM intracellular creatine, this was not sufficient to confer an obvious advantage to the yeast under the specific stress conditions examined here. Second, using arginine kinase, we successfully installed an intracellular phosphagen pool of about 5 mM phosphoarginine. Such arginine kinase-expressing yeast showed improved resistance under two stress challenges that drain cellular energy, which were transient pH reduction and starvation. Although transient starvation led to 50% reduced intracellular ATP concentrations in wild-type yeast, arginine kinase overexpression stabilized the ATP pool at the pre-stress level. Thus, our results demonstrate that temporal energy buffering is an intrinsic property of phosphagen kinases that can be transferred to phylogenetically very distant organisms.