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PubMed1991

Metabolism of poly(3-hydroxyalkanoates) (PHAs) by Pseudomonas oleovorans. Identification and sequences of genes and function of the encoded proteins in the synthesis and degradation of PHA.

Pseudomonas oleovorans accumulates poly(3-hydroxyalkanoates) (PHAs) after growth on medium chain length hydrocarbons. Large amounts of this polyester are synthesized when cells are grown under nitrogen-limiting conditions. When nitrogen is resupplied in the medium, the accumulated PHA is degraded. In this paper, we describe mutants which are defective in the synthesis or in the degradation of PHA. These mutants were used to select DNA fragments which encode PHA polymerases and a PHA depolymerase. A 25-kilobase (kb) DNA fragment was isolated from P. oleovorans that complements a Pseudomonas putida mutant unable to accumulate PHA. Subcloning resulted in the assignment of a 6.4-kb EcoRI fragment as the pha locus, containing genetic information for PHA synthesis. Mutants in the PHA degradation pathway were also complemented by this fragment, indicating that genes encoding PHA biosynthetic and degradative enzymes are clustered. Analysis of the DNA sequence of the 6.4-kb fragment revealed the presence of two open reading frames encoding PHA polymerases based on homology to the poly(3-hydroxybutyrate) polymerase from Alcaligenes eutrophus. A third open reading frame complemented the PHA degradation mutation and is likely to encode a PHA depolymerase. The presence of two PHA polymerases is due to a 2098-base pair DNA duplication. The PHA polymerases are 53% identical and show 35-40% identity to the poly(3-hydroxybutyrate) polymerase. No clear difference in specificity was found for the PHA polymerases. However, with the pha locus cloned on a multicopy vector, a polymer was accumulated that contains a significantly higher amount of substrate-derived monomers. An increase in the rate of polyester synthesis versus oxidation of the monomers in the beta-oxidation explains these findings.

Acyltransferases↗
PubMed1984

Affinity of phytohemagglutinin (PHA) isolectins for serum proteins and regulation of the lectin-induced lymphocyte transformation.

The lectin (PHA) from Phaseolus vulgaris is a tetrameric glycoprotein composed of two different subunits (E and L). The lectin exists as five isolectins (L4, L3E, L2E2, LE3, and E4) that apparently originate from all possible tetrameric combinations of the two subunits. We have investigated two isolectins, PHA-E4 and PHA-L4, with respect to their affinity for human serum glycoproteins, and have subsequently determined how these interactions modulate the ability of the isolectins to induce lymphocyte transformation. PHA-E4 has affinity for 14 identified serum glycoproteins, whereas PHA-L4 exhibited affinity for nine of these proteins. IgM, IgA, IgG, alpha 2-macroglobulin, beta-lipoprotein, and haptoglobin showed the strongest reactivity with PHA-E4; haptoglobin, IgG, and IgA were also the best ligands for PHA-L4. The glycoprotein levels of human serum were then reduced by running the serum over PHA-E4 and PHA-L4 affinity columns, respectively, and the glycoproteins that bound to the two immobilized isolectins were eluted, pooled, and concentrated. The ability of PHA-E4 and PHA-L4 to activate human lymphocytes in the presence of (i) normal human serum, (ii) human serum with reduced levels of glycoproteins, and (iii) human serum with elevated levels of glycoproteins revealed a strong regulatory effect of the glycoproteins on the lymphocyte transformation. When the inhibitory glycoproteins and glycolipids were removed from serum, the mitogenic effect of PHA-E4 increased 200-fold, whereas PHA-L4 exhibited only a 25-fold increase in mitogenic activity. These results show that the so-called "erythroreactive isolectin (PHA-E4)" actually possesses a strong mitogenic activity of its own, but that this has been masked by the interference of serum components.

Blood Proteins↗
PubMedDate not supplied

Alpha-2,6-sialylation of L-PHA reactive oligosaccharides and expression of N-acetylglucosaminyltransferase V in human diffuse large B cell lymphoma.

Cell surface sialylation and beta1-6 branching of L-PHA reactive oligosaccharides play an important role in metastatic capacities of various tumor cell lines. We analyzed the expression and sialylation of L-PHA reactive oligosaccharides in human diffuse large B cell lymphoma (DLBCL). DLBCL was grouped into three types; i). Group A, non-reactive type with no expression of L-PHA reactive oligosaccharides, ii). Group B, sialylated type with expression of sialylated L-PHA reactive oligosaccharides and iii). Group C, non-sialylated type with expression of non-sialylated L-PHA reactive oligosaccharides. To clarify the linkage of sialic acid residues in L-PHA reactive oligosaccharides of Group B cases, L-PHA lectin histochemistry after treatment with two different neuraminidases was performed. In all Group B cases, L-PHA binding reactivity was found after treatment with Vibrio cholerae neuraminidase. But not after treatment with Newcastle disease virus neuraminidase. These data indicate that alpha2,6-linked sialic acid residues were predominantly involved in sialylation of L-PHA reactive oligosaccharides of Group B. To clarify the relationship between expression of N-acetylglucosaminyltransferase V (GnT-V), which catalyzes beta1-6 branching of L-PHA reactive oligosaccharides, and L-PHA reactivities in DLBCL, we investigated the expression of GnT-V using immunohistochemical methods. Most of the Group B and C cases expressed GnT-V while 33% of Group A cases showed no expression of GnT-V. These data suggest that expression of GnT-V is not always correlated with the expression of L-PHA reactive glycoconjugates. Furthermore, survival of patients in Group A which showed no expression of GnT-V was significantly shorter than that of patients in Group C which expressed GnT-V. Therefore, loss of non-sialylated L-PHA reactive oligosaccharides due to lack of expression of GnT-V in lymphoma cells may be associated with aggressiveness of DLBCL.

Biotin↗
PubMed1984

Phaseolus vulgaris phytohaemagglutinin (PHA) binds to the human T lymphocyte antigen receptor.

The interaction of phytohaemagglutinin (PHA) with the human T lymphocyte antigen receptor (Ti) was explored. Nonidet-P40 lysates of surface-labelled HPB-ALL cells were immunoprecipitated with PHA, using a rabbit anti-(PHA)-serum, as well as clonotypic monoclonal antibodies (H1-2D4 and T40/25) and a rabbit antiserum (R-43) against Ti. One- and two-dimensional SDS-polyacrylamide electrophoresis under reducing and non-reducing conditions showed that both the clonotypic antibodies and PHA precipitated a disulphide cross-linked heterodimer having a mol. wt. of approximately 79 000 (unreduced) and a comprising subunits of mol. wts. approximately 50 000 and 39 000 (reduced). Further evidence that PHA binds Ti was obtained by (i) cross-immunodepletion with H1-2D4 and PHA; (ii) immunoprecipitation with H1-2D4 of a glycoprotein fraction specifically eluted from a PHA immunoprecipitate; (iii) immunoprecipitation with PHA of a solubilised H1-2D4 immunoprecipitate; (iv) 2-D (non-equilibrium pH gradient electrophoresis/SDS) analyses of H1-2D4 and PHA immunoprecipitates, indicated that H1-2D4 and PHA recognise coincident beta polypeptides. PHA also binds a Ti-like disulphide cross-linked heterodimer on tonsil lymphocytes and two other T-cell leukaemias (HUT-78 and J6). The data further suggest that PHA and R-43 recognise a subpopulation of Ti molecules on HPB-ALL cells that are not bound by H1-2D4, suggesting that there may be at least two forms of Ti. Similar experiments indicate that Concanavalin A (Con A) and wheat germ agglutinin (WGA) also probably bind Ti, whereas Helix pomatia agglutinin (HPA) does not.

Antibodies, Monoclonal↗
PubMed2004

Polyhydroxyalkanoate (PHA) granule formation in Ralstonia eutropha cells: a computer simulation.

Computer simulation of polyhydroxyalkanoate (PHA) granule formation in vivo could help to design strategies to optimize the fermentation process and achieve higher yields of PHA. It could also suggest biotechnological approaches to control the granule size and molecular weight of the polymer. A computer program simulating the formation of PHA granules inside a Ralstonia eutropha cell was developed, based on published experimental data. The results are applicable to R. eutropha cells or other microorganisms and transgenic plants, where polyhydroxybutyrate production is made possible by heterologous expression systems. The simulation starts at the outset of the PHA accumulation phase when the cells are small and contain no PHA granules. In the presence of abundant glucose, the cell responds to phosphorus limitation by producing 3-hydroxybutyryl-CoA which undergoes polymerization on the few PHA synthase molecules present in the cytoplasm. The amphiphilic PHA synthase-PHA complex attracts additional PHA synthase molecules and granules begin to grow from these initiation sites. Phosphorus limitation and the appearance of PHA in the cytoplasm also stimulate production of phasin molecules that attach themselves to the growing granules. As the granules grow bigger, they begin to touch each other and move to optimize their packing. The phasin coat prevents the granules from coalescing. The size of the cell increases and its prolate ellipsoid shape becomes closer to spherical. The accumulation process stops either when the supply of glucose is exhausted or when the granules become tightly packed within the cell, so that access to their surface is limited. All important variables, such as cell dimensions, granule size, counts of granule-associated molecules, PHA yield, degree of polymerization of the PHA molecules, etc., are recorded in real time during the simulation. Examples of virtual experiments with the cell and their results are shown.

Acyltransferases↗
PubMed1981

Transformation of hemopoietic stem cells by phytohemagglutinin (PHA) II. Mechanism of action.

It has long been known that phytohemagglutinin (PHA) stimulates transformation and growth of immune competent lymphocytes. Lymphoid cell colonies have previously been shown in the spleen with PHA treated lymph node cells from donor mice were injected into irradiated mice. This communication reports the results of in vivo effects of PHA stimulation on agar colony forming units and spleen colony forming units (CFU). C3H/Hej mice injected with 1 ml of PHA-M were found to secrete colony stimulating factors (PHA-CSF) which lead to an increase in the number of agar colony forming units (granulopoiesis). Serum obtained on day 6 after PHA injection showed enhanced granulopoiesis which was four times higher than in the controls. It was found that 1.0 ml and 0.15 ml of PHA-CSF were more effective in promoting the growth of agar colony forming units in agar plates. Intravenous injection of PHA increased the number of spleen-as well as agar colony forming units (CFU). Day 3 appeared to be optimal for in vivo effects of PHA on granulopoietic cells. An increase in the colony forming units was obtainable when previously treated bone marrow and spleen cells taken on day 3 were injected into irradiated mice. There was a fourfold increase of the colony forming units (CFUs) in the spleen and a twofold one in bone marrow cells. As compared to the controls, the increase in agar colony forming units (CFUc) of bone marrow was fourfold and that of the spleen tenfold. On day 5 some effect was still noticeable but it was lower than on day 3. On weight and cell count basis it was found that on day 6 PHA had a significant in vivo effect on the spleen. On the basis of our findings it can be concluded that PHA supports the survival of transplanted stem cells by stimulating their differentiation into unipotent erythroid progenitor cells. It may also be concluded that PHA activates the immune competent stem cells (mostly T lymphocytes) and displays a supporting function for a better stem cell survival and differentiation into the erythroid progenitor cells. The activated lymphocytes secrete a colony-stimulating like factor which stimulates granulopoiesis and also helps in the differentiation of the stem cells.

Animals↗
PubMed1998

pha-4 is Ce-fkh-1, a fork head/HNF-3alpha,beta,gamma homolog that functions in organogenesis of the C. elegans pharynx.

The C. elegans Ce-fkh-1 gene has been cloned on the basis of its sequence similarity to the winged-helix DNA binding domain of the Drosophila fork head and mammalian HNF-3alpha,beta,gamma genes, and mutations in the zygotically active pha-4 gene have been shown to block formation of the pharynx (and rectum) at an early stage in embryogenesis. In the present paper, we show that Ce-fkh-1 and pha-4 are the same gene. We show that PHA-4 protein is present in nuclei of essentially all pharyngeal cells, of all five cell types. PHA-4 protein first appears close to the point at which a cell lineage will produce only pharyngeal cells, independently of cell type. We show that PHA-4 binds directly to a 'pan-pharyngeal enhancer element' previously identified in the promoter of the pharyngeal myosin myo-2 gene; in transgenic embryos, ectopic PHA-4 activates ectopic myo-2 expression. We also show that ectopic PHA-4 can activate ectopic expression of the ceh-22 gene, a pharyngeal-specific NK-2-type homeodomain protein previously shown to bind a muscle-specific enhancer near the PHA-4 binding site in the myo-2 promoter. We propose that it is the combination of pha-4 and regulatory molecules such as ceh-22 that produces the specific gene expression patterns during pharynx development. Overall, pha-4 can be described as an 'organ identity factor', completely necessary for organ formation, present in all cells of the organ from the earliest stages, capable of integrating upstream developmental pathways (in this case, the two distinct pathways that produce the anterior and posterior pharynx) and participating directly in the transcriptional regulation of organ specific genes. Finally, we note that the distribution of PHA-4 protein in C. elegans embryos is remarkably similar to the distribution of the fork head protein in Drosophila embryos: high levels in the foregut/pharynx and hindgut/rectum; low levels in the gut proper. Moreover, we show that pha-4 expression in the C. elegans gut is regulated by elt-2, a C. elegans gut-specific GATA-factor and possible homolog of the Drosophila gene serpent, which influences fork head expression in the fly gut. Overall, our results provide evidence for a highly conserved pathway regulating formation of the digestive tract in all (triploblastic) metazoa.

Animals↗
PubMed2002

Interference between the PHA-4 and PEB-1 transcription factors in formation of the Caenorhabditis elegans pharynx.

PHA-4 is a forkhead/winged helix transcription factor that acts as an organ identity factor in the development of the Caenorhabditis elegans pharynx. PEB-1 is a novel DNA-binding protein also involved in pharyngeal morphogenesis. PHA-4 and PEB-1 bind at overlapping sites on the C183 sequence element that controls pharynx-specific expression of the C. elegans myo-2 gene. It has been suggested that PHA-4 and PEB-1 act cooperatively on the C183 sequence. In this study, we test this model and assess the C183-dependent transcriptional activity of PHA-4 and PEB-1, both individually and in combination. We show that PHA-4 and PEB-1 are both modest transcriptional activators in yeast but that co-expression of the two factors does not result in significantly increased expression of a C183-regulated reporter gene. Electrophoretic mobility-shift assays provide no evidence for the formation of a PHA-4/PEB-1 complex in vitro but rather show that PHA-4 and PEB-1 cannot bind C183 simultaneously. As we have reported previously, ectopic expression of PHA-4 in C. elegans causes ectopic expression of a C183-regulated reporter gene. We show that ectopic expression of PEB-1 cannot cause ectopic expression of the same reporter but rather ectopic PEB-1 inhibits reporter gene activation by PHA-4. Overall, our results do not support a model in which PHA-4 and PEB-1 synergize in vivo but rather support a model in which PEB-1 may negatively modulate PHA-4's ability to activate transcription through C183 during formation of the C. elegans pharynx.

Animals↗
PubMedDate not supplied

Enhancement of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) production in the transgenic Arabidopsis thaliana by the in vitro evolved highly active mutants of polyhydroxyalkanoate (PHA) synthase from Aeromonas caviae.

In this study, the enhancement of photosynthetic PHA production was achieved using the highly active mutants of PHA synthase created by the in vitro evolutionally techniques. The wild-type and mutated PHA synthase genes from Aeromonas caviae were introduced into Arabidopsis thaliana together with the NADPH-dependent acetoacetyl-CoA reductase gene from Ralstonia eutropha. Expression of the highly active mutated PHA synthase genes, N149S and D171G, led to an 8-10-fold increase in PHA content in the T1 transgenic Arabidopsis, compared to plants harboring the wild-type PHA synthase gene. In homozygous T2 progenies, PHA content was further increased up to 6.1 mg/g cell dry weight. GC/MS analysis of the purified PHA from the transformants revealed that these PHAs were poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [P(3HB-co-3HV)] copolymers consisting of 0.2-0.8 mol % 3HV. The monomer composition of the P(3HB-co-3HV) copolymers synthesized by the wild-type and mutated PHA synthases reflected the substrate specificities observed in Escherichia coli. These results indicate that in vitro evolved PHA synthases can enhance the productivity of PHA and regulate the monomer composition in transgenic plants.

Acyltransferases↗
PubMed1997

Synthesis of poly(3-hydroxyalkanoates) in Escherichia coli expressing the PHA synthase gene phaC2 from Pseudomonas aeruginosa: comparison of PhaC1 and PhaC2.

In order to obtain functional expression of PHA synthase gene phaC2 from Pseudomonas aeruginosa in Escherichia coli, the coding region of phaC2 was subcloned, including the ribosomal binding site, into pBluescript SK- collinear to the lac promoter. This plasmid pBHR71-C2 enabled functional expression of phaC2 in E. coli LS1298 (fadB) under lac promoter control, leading to PHA accumulation, when grown in LB medium containing 0.5% (w/v) of various fatty acids (C8-C14). The strongest accumulation of PHA was observed, when dodecanoate was provided as carbon source, and PHA contributed to 15% of cell dry weight, which was composed of 35 mol% 3-hydroxydodecanoate, 60 mol% 3-hydroxydecanoate and 5 mol% 3-hydroxyoctanoate. Plasmid pBHR78, which contained both genes phaC1 and phaC2 from P. aeruginosa under lac promoter control in pBluescript SK- led in E. coli LS1298 to PHA accumulation, which contributed to 13% of cell dry weight, when cells were grown on decanoate. Only slight differences in PHA composition compared with either PhaC1 or PhaC2 were obtained. The weight average molecular masses of PHA purified from decanoate-grown cells of E. coli LS1298 expressing PhaC1 or PhaC2 alone or both PHA synthases, were 106 x 10(3), 70 x 10(3) or 67 x 10(3), respectively. This study clearly demonstrated that both PHA synthases from P. aeruginosa exhibit very similar properties resulting in similar extent of PHA accumulation, similar composition and molecular mass, when expressed in E. coli and that fatty acid beta-oxidation provides substrates for both PHA synthases.

Acyltransferases↗
PubMed1998

Projections from dorsomedial part of the subnucleus oralis to the mesencephalic trigeminal neurons innervating the masseter muscle--a PHA-L and HRP double labeling study in the rat.

When PHA-L was injected to dorsomedial part of the subnucleus oralis of the spinal trigeminal nucleus (Vodm), anterogradely labeled varicosities and boutons were observed in the mesencephalic trigeminal nucleus (Vme). The PHA-L labeling was seen mainly in the Vine ipsilateral to the injection side. If the injection sites were placed more medially containing both Vodm and parvocellular reticular nucleus (PCRt), more PHA-L labeling in contralateral Vme was observed. It appeared that the Vodm neurons projected predominantly to the ipsilateral Vme, while neurons in the PCRt adjacent to the Vodm projected bilaterally to the Vme. It was also seen that many PHA-L labeled varicosities and boutons surrounded or contacted on the Vme neurons counterstained with cresyl violet. These contacts were seen frequently in the ipsilateral Vme, occasionally in the contralateral nucleus. Some Vme neurons ipsilateral to the injection side were retrogradely labeled in a solidly-filled appearance following injection of PHA-L into the Vodm. When PHA-L was applied to the Vodm and HRP was injected to the masseter nerve on the same side, the relationship between PHA-L labeled terminals and HRP labeled Vme neurons was studied. The contacts between PHA-L labeled boutons and HRP labeled somata or processes of the Vme neurons were observed occasionally. PHA-L labeled terminals sometimes contacted on none-HRP-labeled somata counterstained with neutral red. Besides the PHA-L labeling in the Vme, the labeling was also seen in the medial parabrachial nucleus ipsilaterally, in the motor trigeminal nucleus bilaterally with ipsilateral predominance. In addition, an outstanding labeling band along the medial border of the principal sensory trigeminal nucleus (Vp) was observed following injection of PHA-L into the Vodm. The labeled terminals were concentrated in dorsomedial part of the Vp (Vpdm) and in juxtatrigeminal nucleus (JX), meanwhile many labeled fibres were distributed between the Vpdm and JX in the intertrigeminal region.

Animals↗
PubMed2006

Inactivation of type I polyhydroxyalkanoate synthase in Aeromonas hydrophila resulted in discovery of another potential PHA synthase.

Aeromonas hydrophila CGMCC 0911 possessing type I polyhydroxyalkanoate (PHA) synthase (PhaC) produced only PHBHHx from lauric acid but not from glucose. Medium-chain-length (mcl) PHA was produced from lauric acid or glucose only when PhaC of A. hydrophila was inactivated, indicating the existence of another PHA synthase in the wild type. Using PCR cloning strategy, the potential PHA synthase gene (phaC (mcl)) was obtained from genomic DNA of the wild type and exhibited strong homology to type II PHA synthase genes of Pseudomonas strains. The phaC (mcl) gene was PCR subcloned into plasmid pBBR1MCS2 and expressed in a PHA-negative mutant of Pseudomonas putida. Recombinant P. putida synthesized mcl PHA from gluconate or octanoate. This result proved that wild type A. hydrophila possessed another type II PHA synthase, which was responsible for the synthesis of mcl PHA, besides type I PHA synthase.

Acyltransferases↗
PubMed2006

Safety testing of GM-rice expressing PHA-E lectin using a new animal test design.

The 90-day animal study is the core study for the safety assessment of genetically modified foods in the SAFOTEST project. The model compound tested in the 90-day study was a rice variety expressing the kidney bean Phaseolus vulgaris lectin agglutinin E-form (PHA-E lectin). Female Wistar rats were given a nutritionally balanced purified diet with 60% parental rice, 60% PHA-E rice or 60% PHA-E rice spiked with 0.1% recombinant PHA-E lectin for 90 days. This corresponded to a mean daily PHA-E lectin intake of approximately 0, 30 and 100mg/kg body weight for each group, respectively. The spiking was used to increase the specificity and to demonstrate the sensitivity of the study. A range of biological, biochemical, microbiological and pathological parameters were examined and significant differences in weight of small intestine, stomach and pancreas and plasma biochemistry were seen between groups. Included in this paper are also data from the molecular characterisation and chemical analysis of the PHA-E rice, from the construction and production of the PHA-E lectin, and from the preceding 28-day in vivo study where the toxicity of the pure PHA-E lectin was determined. In conclusion, the combined use of information from the compositional analysis, the 28-day study and the characterisation of the PHA-E rice and the PHA-E lectin has improved the design of the 90-day study. The spiking procedure has facilitated the interpretation of the results of the study and transferred it into a valuable tool for the future safety testing of genetically modified foods.

Animals↗
PubMed2004

pha-2 encodes the C. elegans ortholog of the homeodomain protein HEX and is required for the formation of the pharyngeal isthmus.

The pha-2 mutant was isolated in 1993 by Leon Avery in a screen for worms with visible defects in pharyngeal feeding behavior. In pha-2 mutant worms, the pharyngeal isthmus is abnormally thick and short and, in contrast to wild-type worms, harbors several cell nuclei. We show here that pha-2 encodes a homeodomain protein and is homologous to the vertebrate homeobox gene, Hex (also known as Prh). Consistent with a function in pharyngeal development, the pha-2 gene is expressed in the pharyngeal primordium of Caenorhabditis elegans embryos, particularly in pm5 cells that form the bulk of the isthmus. We show that in the pha-2 mutant there is a failure of the pm5 cells to elongate anteriorly while keeping their nuclei within the nascent posterior bulb to form the isthmus during the 3-fold embryonic stage. We also present evidence that pha-2 regulates itself positively in pm5 cells, that it is a downstream target of the forkhead gene pha-4, and that it may also act in the isthmus as an inhibitor of the ceh-22 gene, an Nkx2.5 homolog. Finally, we have begun characterizing the regulation of the pha-2 gene and find that intronic sequences are essential for the complete pha-2 expression profile. The present report is the first to examine the expression and function of an invertebrate Hex homolog, that is, the C. elegans pha-2 gene.

Amino Acid Sequence↗
PubMed2006

Misexpression of acetylcholinesterases in the C. elegans pha-2 mutant accompanies ultrastructural defects in pharyngeal muscle cells.

pha-2 is the Caenorhabditis elegans homolog of the vertebrate homeobox gene Hex. Embryonic expression of pha-2 is mostly pharyngeal and the only described mutant allele of pha-2 results in a severe pharyngeal defect in which certain muscle cells (pm5 cells) and neurons are grossly deformed. Here, we performed a detailed characterization of the pha-2 phenotype using cell-type-specific reporters, physical manipulation of the nuclei in pharyngeal muscle cells using "optical tweezers", electron microscopy, staining of the actin cytoskeleton as well as phenotypic rescue and ectopic expression experiments. The main findings of the present study are (i) the pha-2 (ad472) mutation specifically impairs the pharyngeal expression of pha-2; (ii) in the pha-2 mutant, the cytoskeleton of the pm5 cells is measurably weaker than in normal cells and is severely disrupted by large tubular structures and organelles; (iii) the pm5 cells of the pha-2 mutant fail to express the acetylcholinesterase genes ace-1 and ace-2; (iv) ectopic expression of pha-2 can induce ectopic expression of ace-1 and ace-2; and (v) the anc-1 mutant with mislocalized pm5 cell nuclei occasionally shows an isthmus phenotype similar to that of pha-2 worms.

Acetylcholinesterase↗
PubMedDate not supplied

Poly(hydroxyalkanoic acid) Biosynthesis in Ectothiorhodospirashaposhnikovii: Characterization and Reactivity of a Type III PHA Synthase.

Ectothiorhodospira shaposhnikovii is able to accumulate polyhydroxybutyrate (PHB) photoautotrophically during nitrogen-limited growth. The activity of polyhydroxyalkanoate (PHA) synthase in the cells correlates with PHB accumulation. PHA synthase samples collected during the light period do not show a lag phase during in vitro polymerization. Synthase samples collected in the dark period displays a significant lag phase during in vitro polymerization. The lag phase can be eliminated by reacting the PHA synthase with the monomer, 3-hydroxybutyryl-CoA (3HBCoA). The PHA synthase genes (phaC and phaE) were cloned by screening a genomic library for PHA accumulation in E. coli cells. The PHA synthase expressed in the recombinant E. coli cells was purified to homogeneity. Both sequence analysis and biochemical studies indicated that this PHA synthase consists of two subunits, PhaE and PhaC and, therefore, belongs to the type III PHA synthases. Two major complexes were identified in preparations of purified PHA synthase. The large complex appears to be composed of 12 PhaC subunits and 12 PhaE subunits (dodecamer), whereas the small complex appears to be composed of 6 PhaC and 6 PhaE subunits (hexamer). In dilute aqueous solution, the synthase is predominantly composed of hexamer and has low activity accompanied with a significant lag period at the initial stage of reaction. The percentage of dodecameric complex increases with increasing salt concentration. The dodecameric complex has a greatly increased specific activity for the polymerization of 3HBCoA and a negligible lag period. The results from in vitro polymerizations of 3HBCoA suggest that the PHA synthase from E. shaposhnikovii may catalyze a living polymerization and demonstrate that two PhaC and two PhaE subunits comprise a single catalytic site in the synthase complex.

Acyltransferases↗
PubMed2002

Regulation of phasin expression and polyhydroxyalkanoate (PHA) granule formation in Ralstonia eutropha H16.

Regulation of expression of the phasin PhaP, which is the major protein at the surface of polyhydroxyalkanoate (PHA) granules in Ralstonia eutropha H16, was studied and analysed at the molecular level. The regulation of PhaP expression is achieved by an autoregulated repressor, which is encoded by phaR in R. eutropha. The occurrence of PhaR homologues and the organization of phaR genes was analysed in detail in 29 different bacteria. Three kinds of molecule to which PhaR binds were identified in cells of R. eutropha, as revealed by gel-mobility-shift assays, DNaseI footprinting, cell fractionation, immunoelectron microscopy studies employing anti-PhaR antibodies raised against purified N-terminal hexahistidine-tagged PhaR and in vitro binding studies employing artificial PHA granules. PhaR binds upstream of phaP at two sites comprising the transcriptional start site plus the -10 region and a region immediately upstream of the -35 region of the sigma(70) promoter of phaP, where two imperfect 12 bp repeat sequences (GCAMMAAWTMMD) were identified on the sense and anti-sense strands. PhaR also binds 86 bp upstream of the phaR translational start codon, where the sigma(54)-dependent promoter was identified. PhaR also binds to the surface of PHA granules. In the cytoplasm of a phaROmegaKm mutant of R. eutropha H16, increased quantities of PhaP were detected and the cells formed by this strain were much smaller and had many more PHA granules present than the wild-type. These data support the following model for the regulation of phaP expression. Under cultivation conditions not permissive for PHA biosynthesis or in mutants defective in PHA biosynthesis, PhaR binds to the phaP promoter region and represses transcription of this gene. After the onset of PHA biosynthesis, under conditions that are permissive for the formation of nascent granules, PhaR binds to PHA granules and phaP is transcribed. At the later stages of PHA accumulation, PhaR no longer binds to the granules and the transcription of phaP is again repressed. In addition to this, phaR expression is subject to autoregulation. Excess PhaR that has not bound to the phaP upstream region or to PHA granules binds to the phaR upstream region, thereby repressing its own transcription.

Bacterial Proteins↗
PubMed2000

Analysis of in vivo substrate specificity of the PHA synthase from Ralstonia eutropha: formation of novel copolyesters in recombinant Escherichia coli.

In order to investigate the in vivo substrate specificity of the type I polyhydroxyalkanoate (PHA) synthase from Ralstonia eutropha, we functionally expressed the PHA synthase gene in various Escherichia coli mutants affected in fatty acid beta-oxidation and the wild-type. The PHA synthase gene was expressed either solely (pBHR70) or in addition to the R. eutropha genes encoding beta-ketothiolase and acetoacetyl-coenzyme A (CoA) reductase comprising the entire PHB operon (pBHR68) as well as in combination with the phaC1 gene (pBHR77) from Pseudomonas aeruginosa encoding type II PHA synthase. The fatty acid beta-oxidation route was employed to provide various 3-hydroxyacyl-CoA thioesters, depending on the carbon source, as in vivo substrate for the PHA synthase. In vivo PHA synthase activity was indicated by PHA accumulation and substrate specificity was revealed by analysis of the comonomer composition of the respective polyester. Only in recombinant E. coli fad mutants harboring plasmid pBHR68, the R. eutropha PHA synthase led to accumulation of poly(3-hydroxybutyrate-co-3-hydroxyoctanoate) (poly(3HB-co-3HO)) and poly(3HB-co-3HO-co-3-hydroxydodecanoate (3HDD)), when octanoate and decanoate or dodecanoate were provided as carbon source, respectively. Coexpression of phaC1 from P. aeruginosa indicated and confirmed the provision of PHA precursor via the beta-oxidation pathway and led to the accumulation of a blend of two different PHAs in the respective E. coli strain. These data strongly suggested that R. eutropha PHA synthase accepts, besides the main substrate 3-hydroxybutyryl-CoA, also the CoA thioesters of 3HO and 3HDD.

Acyltransferases↗