P2 Particles Research Articles

How pirate phage interferes with helper phage: Comparison of the two distinct strategies

Pirate phages use the structural proteins encoded by unrelated helper phages to propagate. The best-studied example is the pirate P4 and helper P2 of coliphages, and it has been known that the Staphylococcus aureus pathogenicity islands (SaPIs) that can encode virulence factors act as pirate phages, too. When alone in the host, the pirate phages act as a prophage, but when the helper phage gene is also in the same host cell, the pirate phage has ability to exploit the helper phages structural proteins to produce pirate phage particles and spread, interfering with the helper phage production. The known helper phages in these systems are temperate phages. Interestingly, the interference of the pirate phage to the helper phage occurs in a different manner between the SaPI-helper system and the P4-P2 system. SaPIs cannot lyse a helper lysogen upon infection, while when a helper phage lyse a SaPI lysogen, most of the phage particles produced are the SaPI particles. On the contrary, in the P4-P2 system, a pirate phage P4 can lyse a helper P2 lysogen to produce mostly the P4 particles, while when P2 phage lyses a P4 lysogen, most of the produced phages are the P2 particles. Here, the consequences of these different strategies in the pirate and helper phage spreading among uninfected host is analyzed by using mathematical models. It is found that SaPI’s strategy interferes with the helper phage spreading significantly more than the P4’s strategy, because SaPI interferes with the helper phage’s main reproduction step, while P4 interferes only by forcing the helper lysogens to lyse. However, the interference is found to be weaker in the spatially structured environment than in the well-mixed environment. This is because, in the spatial setting, the system tends to self-organize so that the helper phages take over the front of propagation due to the need of helper phage for the pirate phage spreading.

Dendrimer-doxorubicin conjugates exhibit improved anticancer activity and reduce doxorubicin-induced cardiotoxicity in a murine hepatocellular carcinoma model.

Hepatocellular carcinoma (HCC) is the 2nd leading cause of cancer-related deaths every year globally. The most common form of treatment, hepatic arterial infusion (HAI), involves the direct injection of doxorubicin (DOX) into the hepatic artery. It is plagued with limited therapeutic efficacy and the occurrence of severe toxicities (e.g. cardiotoxicity). We aim to improve the therapeutic index of DOX delivered via HAI by loading the drug onto generation 5 (G5) poly(amidoamine) (PAMAM) dendrimers targeted to hepatic cancer cells via N-acetylgalactosamine (NAcGal) ligands. DOX is attached to the surface of G5 molecules via two different enzyme-sensitive linkages, L3 or L4, to achieve controllable drug release inside hepatic cancer cells. We previously reported on P1 and P2 particles that resulted from the combination of NAcGal-targeting with L3- or L4-DOX linkages, respectively, and showed controllable DOX release and toxicity towards hepatic cancer cells comparable to free DOX. In this study, we demonstrate that while the intratumoral delivery of free DOX (1 mg/kg) into HCC-bearing nod scid gamma (NSG) mice achieves a 2.5-fold inhibition of tumor growth compared to the saline group over 30 days, P1 and P2 particles delivered at the same DOX dosage achieve a 5.1- and 4.4-fold inhibition, respectively. Incubation of the particles with human induced pluripotent stem cell derived cardiomyocytes (hiPSC CMs) showed no effect on monolayer viability, apoptosis induction, or CM electrophysiology, contrary to the effect of free DOX. Moreover, magnetic resonance imaging revealed that P1- and P2-treated mice maintained cardiac function after intraperitoneal administration of DOX at 1 mg/kg for 21 days, unlike the free DOX group at an equivalent dosage, confirming that P1/P2 can avoid DOX-induced cardiotoxicity. Taken together, these results highlight the ability of P1/P2 particles to improve the therapeutic index of DOX and offer a replacement therapy for clinical HCC treatment.

Preparation of hierarchical porous Zn-salt particles and their superhydrophobic performance

Superhydrophobic surfaces arranged by hierarchical porous particles were prepared using modified hydrothermal routes under the effect of sodium citrate. Two particle samples were generated in the medium of hexamethylenetetramine (P1) and urea (P2), respectively. X-ray diffraction, scanning electron microscope, and transmission electron microscope were adopted for the investigation, and results revealed that the P1 and P2 particles are porous microspheres with crosslinked extremely thin (10–30nm) sheet crystals composed of Zn5(OH)8Ac2·2H2O and Zn5(CO3)2(OH)6, respectively. The prepared particles were treated with a fluoroethylene vinyl ether derivative and studied using Fourier transform infrared spectroscopy and energy-dispersive X-ray spectrometer. Results showed that the hierarchical surfaces of these particles were combined with low-wettable fluorocarbon layers. Moreover, the fabricated surface composed of the prepared hierarchical particles displayed considerably high contact angles, indicating great superhydrophobicity for the products. The wetting behavior of the particles was analyzed with a theoretical wetting model in comparison with that of chestnut-like ZnO products obtained through a conventional hydrothermal route. Correspondingly, this study provided evidence that high roughness surface plays a great role in superhydrophobic behavior.

The Particle γάρ: From Ancient Greek Sentence Connector to Blatant Line Filler? A Case-study on the Late Medieval Greek Chronicle of Morea

Ancient Greek is widely regarded as a language with an extraordinary number of so-called “Wackernagel P2 particles” such as γάρ, δ(έ), and μέν, which serve a multitude of discourse functions. From the post-Classical period on, however, these small words gradually lose their importance in discourse and die out. This is reflected in the interest of scholars: while there are many studies on particles in older stages of Greek, not much research has been conducted on the particles in late medieval Greek (LMG; twelfth to fifteenth centuries). At this stage of the Greek language, the P2 particles are acknowledged to no longer be part of the living spoken language. Nonetheless, some of these small words still turn up in texts written in the vernacular. Since most LMG vernacular literature is composed in the metre of the 15-syllabic πολιτικὸς στίχος (vernacular prose being extremely scarce in this period), these occurrences are traditionally explained by appealing to metrical and/or stylistic reasons: the particles constitute archaizing relics merely inserted to give a classicizing flavour to the text, or are even used “metri causa”, simply to achieve the required number of syllables. In this note, I present a case-study on the “explanatory” particle γάρ (“for”) in the Chronicle of Morea, the best-known verse chronicle of the Greek Middle Ages. I show that γάρ is more than a blatant line filler. First, γάρ is not at all distributed at random, but consistently occupies P2 and thus obeys the so-called “Law of Wackernagel”, as the particles in Ancient Greek do. Moreover, γάρ can still exert a clear discourse function, albeit often a different one than in Ancient Greek.

Effect of pH, citrate treatment and silane-coupling agent concentration on the magnetic, structural and surface properties of functionalized silica-coated iron oxide nanocomposite particles

Superparamagnetic iron oxide nanoparticles were synthesized by coprecipitation of iron chloride salts at various pH values (9, 10, 11 and12) that were adjusted using an ammonia solution. Increasing the pH from 9 to 12 led to decreases in the size of iron oxide nanoparticles from 7.9±1.4 to 5±0.6 nm and the saturation magnetization ( M s ) from 82.73 to 67.14 emu/g, respectively, when analyzed with transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM). X-ray diffraction patterns as well as M s values showed that magnetite is the dominantly synthesized phase in the examined pH values. Unmodified iron oxide nanoparticles were coated with silica via the hydrolysis and condensation of tetraethyl orthosilicate (TEOS), designated P1 particles. The size distribution diagram of P1 particles showed two regions with mean sizes of 143.3±15.4 and 216.9±13.7 nm corresponding to silica and iron oxide@silica particles, respectively. Stabilization of iron oxide nanoparticles using sodium citrate prior to coating with silica (P2 particles) resulted in nanocomposites with a mean size of 275±16.1 nm and an M s value of 2.9 emu/g. Subsequently, the surface of P2 particles was functionalized by amine groups using N-(2-aminoethyl)-3-aminopropyltrimethoxysilane (EDS). Results obtained from the measurement of zeta potential revealed that the highest value of isoelectric point (PI) change, indicating a more efficient surface functionalization, occurs when the EDS concentration of 90 mM is used, as compared to that for particles aminated using 25 and 180 mM EDS.

Cylindrical inclusion protein of potato virus A is associated with a subpopulation of particles isolated from infected plants

Potato virus A (PVA) particles were purified by centrifugation through a 30 % sucrose cushion and the pellet (P1) was resuspended and sedimented through a 5-40 % sucrose gradient. The gradient separation resulted in two different virus particle populations: a virus fraction (F) that formed a band in the gradient and one that formed a pellet (P2) at the bottom of the gradient. All three preparations contained infectious particles that retained their integrity when visualized by electron microscopy (EM). Western blotting of the P1 particles revealed that the viral RNA helicase, cylindrical inclusion protein (CI), co-purified with virus particles. This result was confirmed with co-immunoprecipitation experiments. CI was detected in P2 particle preparations, whereas F particles were devoid of detectable amounts of CI. ATPase activity was detected in all three preparations with the greatest amount in P2. Results from immunogold-labelling EM experiments suggested that a fraction of the CI present in the preparations was localized to one end of the virion. Atomic force microscopy (AFM) studies showed that P1 and P2 contained intact particles, some of which had a protruding tip structure at one end, whilst F virions were less stable and mostly appeared as beaded structures under the conditions of AFM. The RNA of the particles in F was translated five to ten times more efficiently than RNA from P2 particles when these preparations were subjected to translation in wheat-germ extracts. The results are discussed in the context of a model for CI-mediated functions.

Release of extracellular membrane particles carrying the stem cell marker prominin-1 (CD133) from neural progenitors and other epithelial cells

Apical plasma membrane constituents of mammalian neural stem/progenitor cells have recently been implicated in maintaining their stem/progenitor cell state. Here, we report that in the developing embryonic mouse brain, the fluid in the lumen of the neural tube contains membrane particles carrying the stem cell marker prominin-1 (CD133), a pentaspan membrane protein found on membrane protrusions of the apical surface of neuroepithelial cells. Two size classes of prominin-1-containing membrane particles were observed in the ventricular fluid: approximately 600-nm particles, referred to as P2 particles, and 50-80-nm vesicles, referred to as P4 particles. The P2 and P4 particles appeared in the ventricular fluid at the very onset and during the early phase of neurogenesis, respectively. Concomitant with their appearance, the nature of the prominin-1-containing apical plasma membrane protrusions of neuroepithelial cells changed, in that microvilli were lost and large pleiomorphic protuberances appeared. P4 particles were found in various body fluids of adult humans, including saliva, seminal fluid and urine, and were released by the epithelial model cell line Caco-2 upon differentiation. Importantly, P4 particles were distinct from exosomes. Our results demonstrate the widespread occurrence of a novel class of extracellular membrane particles containing proteins characteristic of stem cells, and raise the possibility that the release of the corresponding membrane subdomains from the apical surface of neural progenitors and other epithelial cells may have a role in tissue development and maintenance. Moreover, the presence of prominin-1-containing membrane particles in human body fluids may provide the basis for a protein-based diagnosis of certain diseases.

Blood changes in mallards exposed to white phosphorus

AbstractWhite phosphorus (P4) has been extensively used by the military for various purposes, including marking artillery impacts and as an obscurant. Target practice in an Alaskan tidal marsh during the last 4 decades has deposited large amounts of P4 particles in sediments and water, which have resulted in die‐offs of several waterfowl species. Because the toxicity of P4 in birds has not been well documented and because it is quickly excreted or metabolized in living animals, we sought to determine the effects of experimental dosing on blood characteristics in game farm mallards (Anas platyrhynchos). In two experiments, one employing single doses of 5.4 mg P4 per kilogram body weight in corn oil and the other using daily repeated doses of pelletized P4 at either 0.5 or 1.0 mg/kg, there were significant changes in aspartate aminotransferase, alanine aminotransferase, lactate dehydrogenase (LDH), inorganic P, hematocrit, and hemoglobin. Other indications of exposure included changes in uric acid, creatinine, and total protein, which were consistent with reported liver and kidney damage due to this contaminant. Changes in white blood cells included a greater frequency of thrombocytes and fewer lymphocytes in dosed birds compared to controls. A biomarker of exposure based on LDH activity and hemoglobin is proposed.

BLOOD CHANGES IN MALLARDS EXPOSED TO WHITE PHOSPHORUS

White phosphorus (P4) has been extensively used by the military for various purposes, including marking artillery impacts and as an obscurant. Target practice in an Alaskan tidal marsh during the last 4 decades has deposited large amounts of P4 particles in sediments and water, which have resulted in die-offs of several waterfowl species. Because the toxicity of P4 in birds has not been well documented and because it is quickly excreted or metabolized in living animals, we sought to determine the effects of experimental dosing on blood characteristics in game farm mallards (Anas platyrhynchos). In two experiments, one employing single doses of 5.4 mg P4 per kilogram body weight in corn oil and the other using daily repeated doses of pelletized P4 at either 0.5 or 1.0 mg/kg, there were significant changes in aspartate aminotransferase, alanine aminotransferase, lactate dehydrogenase (LDH), inorganic P, hematocrit, and hemoglobin. Other indications of exposure included changes in uric acid, creatinine, and total protein, which were consistent with reported liver and kidney damage due to this contaminant. Changes in white blood cells included a greater frequency of thrombocytes and fewer lymphocytes in dosed birds compared to controls. A biomarker of exposure based on LDH activity and hemoglobin is proposed.

Isothermal Oxidation of White Phosphorus Dispersed in Water in a Stirred-Tank Reactor

ABSTRACT A global, first-order kinetic model was found to fit the data for the isothermal wet oxidation of elemental white phosphorus (P4) in a batch, stirred-tank reactor. The initial concentration of white phosphorus solids was held constant at 1 g/L and an air flow of 2.0 standard liters per minute was used to supply the oxygen for the reaction. A CD6-like turbine and an A2 impeller were evaluated at speeds from 1000-2250 rpm. For the CD6-like turbine, mass transfer effects were assumed to be eliminated above 2000 rpm. Thus, the CD6-like turbine with a speed of 2250 rpm was selected for the isothermal studies. Particle size and temperature were varied. For the isothermal conditions, the first order kinetic constant varied from 0.022 min-1 at 46 °C to 0.078 min-1 at 80 °C. The apparent activation energy was 6.78 kcal/mol. Oxygen reacted with the suspended P4 particles forming oxides of phosphorus, primarily phosphorus pentoxide (P4010 or P2 O5). Some of the P2O5 reacted with the water to form PO4 3- as the primary product of white phosphorus oxidation. The amount of phosphorus pentoxide absorbed in the water increased with temperature. The rate of phosphate formation followed zero order kinetics and was independent of particle size. As the temperature increased, the ratio of PO4/ PO3 increased. This observation and the apparently low activation energy suggest that diffusion effects may not have been eliminated completely.

The N-Terminal Part of Bacteriophage P2 Capsid Protein Is Essential for Postassembly Maturation of P2 and P4 Capsids

During capsid assembly of bacteriophage P2 and its satellite phage P4, gpN undergoes proteolytic cleavage with the removal of the first 31 amino acids. The truncated protein gpN* is unable to support formation of viable phages in complementation tests. A c-myc antigenic epitope (EQKLISEEDL) exchanged for eleven amino acids in the amino terminal part of gpN results in both proteolytic processing of gpN::c-myc as well as assembly of P2 and P4 procapsid-like structures, but gpN::c-myc failed, like N*, to support the production of infectious P2 and P4 particles.

Persistence of white phosphorus (P4) particles in salt marsh sediments

AbstractRemediation of sediments at Eagle River Flats, Alaska, a salt marsh contaminated with solid particles of white phosphorus (P4), may require severe alterations of the wetland by dredging, draining, or covering. However, some sediments may undergo decontamination naturally in areas that are seasonally subaerially exposed. The persistence of millimeter‐size P4 particles was studied in laboratory and field experiments. White phosphorus particles were found to be persistent in saturated sediments. In unsaturated sediments, loss was rapid (within 24 h) at 20°C, and was retarded by low temperatures.

Mechanisms of genome propagation and helper exploitation by satellite phage P4

Temperate coliphage P2 and satellite phage P4 have icosahedral capsids and contractile tails with side tail fibers. Because P4 requires all the capsid, tail, and lysis genes (late genes) of P2, the genomes of these phages are in constant communication during P4 development. The P4 genome (11,624 bp) and the P2 genome (33.8 kb) share homologous cos sites of 55 bp which are essential for generating 19-bp cohesive ends but are otherwise dissimilar. P4 turns on the expression of helper phage late genes by two mechanisms: derepression of P2 prophage and transactivation of P2 late-gene promoters. P4 also exploits the morphopoietic pathway of P2 by controlling the capsid size to fit its smaller genome. The P4 sid gene product is responsible for capsid size determination, and the P2 capsid gene product, gpN, is used to build both sizes. The P2 capsid contains 420 capsid protein subunits, and P4 contains 240 subunits. The size reduction appears to involve a major change of the whole hexamer complex. The P4 particles are less stable to heat inactivation, unless their capsids are coated with a P4-encoded decoration protein (the psu gene product). P4 uses a small RNA molecule as its immunity factor. Expression of P4 replication functions is prevented by premature transcription termination effected by this small RNA molecule, which contains a sequence that is complementary to a sequence in the transcript that it terminates.

Mechanisms of genome propagation and helper exploitation by satellite phage P4.

Temperate coliphage P2 and satellite phage P4 have icosahedral capsids and contractile tails with side tail fibers. Because P4 requires all the capsid, tail, and lysis genes (late genes) of P2, the genomes of these phages are in constant communication during P4 development. The P4 genome (11,624 bp) and the P2 genome (33.8 kb) share homologous cos sites of 55 bp which are essential for generating 19-bp cohesive ends but are otherwise dissimilar. P4 turns on the expression of helper phage late genes by two mechanisms: derepression of P2 prophage and transactivation of P2 late-gene promoters. P4 also exploits the morphopoietic pathway of P2 by controlling the capsid size to fit its smaller genome. The P4 sid gene product is responsible for capsid size determination, and the P2 capsid gene product, gpN, is used to build both sizes. The P2 capsid contains 420 capsid protein subunits, and P4 contains 240 subunits. The size reduction appears to involve a major change of the whole hexamer complex. The P4 particles are less stable to heat inactivation, unless their capsids are coated with a P4-encoded decoration protein (the psu gene product). P4 uses a small RNA molecule as its immunity factor. Expression of P4 replication functions is prevented by premature transcription termination effected by this small RNA molecule, which contains a sequence that is complementary to a sequence in the transcript that it terminates.

The polarity suppression factor of bacteriophage P4 is also a decoration protein of the P4 capsid

We show that the product of the polarity suppression ( psu) gene from bacteriophage P4 associates with P4 capsids. This association can occur when Psu is (i) provided in vivo from the P4 genome or from a plasmid or (ii) provided in vitro by mixing viable phage particles with Psu protein. Psu is unable to associate with the larger capsid of P4's helper phage P2. Discrimination of the P4 and P2 capsids by Psu appears to be independent of the presence of the P4 genome in the capsid, since P2 size capsids filled with P4 DNA cannot accommodate Psu association. P4 psu particles devoid of Psu are less stable than P4 particles carrying Psu. These results indicate that, in addition to its antitermination activity at Rho-dependent terminators, Psu is also a decoration protein that stabilizes the P4 capsids.

Bacteriophage P2 and P4 morphogenesis: Protein processing and capsid size determination

An interesting feature of the bacteriophage P2–P4 system is the switch in size between a large P2 (60 nm) and a small P4 (45 nm) capsid. We have investigated whether the protein processing reactions cleaving the primary translation product gpN to several capsid proteins (h1, h2, and N ∗) are involved in this switch. Using antibodies specific against gpN and its derivatives we have identified all the structural components of mature P2 and P4 particles that are derived from gpN. Our estimate of the relative amounts of gpN derivatives suggests that the previously identified minor capsid proteins h1 and h2 can only be essential structural components of the P4, and not the P2, capsid. Nevertheless, the relative amounts are similar in vivo during a P2 and a P4 infection. This indicates that the switch in head size is not caused by the presence of elevated amounts of hi and h2 during P4 morphogenesis. We have also identified the sites where gpN is cleaved to its derivatives h1, h2, and N ∗, ascertaining that the cleavage sites are the same in P2 and P4. Our results indicate that the processing reactions are not directly involved in the head size determination mechanism.

Synthesis of native 60S and 40S ribosomal subunits in Yoshida rat ascites hepatoma AH-130 cells: Correlation with the rate of cell growth

The 60Sn and 40Sn subunit ribosome synthesis declined significantly in Yoshida rat ascites hepatoma AH-130 cells from the log phase to the plateau phase of the in vivo growth. Two main classes of 40Sn particles with protein/RNA ratios of 1.82 (p2) and 1.20 (p3) and a minor “heavy” one with protein/RNA ratio of 0.96 (p1) could be distinguished reproducibly by their ultraviolet absorption after sucrose zone sedimentation. The p2 particles appeared the dominating class in log phase cells. In plateau phase cells a decrease of p2 and an increase of p3 particles was observed. Under these conditions the p1 particles and the peaks corresponding to 60Sn subunits and to 80S ribosomes were also increased. Newly synthetized 40Sn particles banded in the p3 region of the gradient and p2 particles originated from them. These particles entered into the ribosomal cycle and contained poly(A) RNA. Formation of radioactive 80S couples by subunits entering into the ribosomal cycle was markedly stimulated in log phase cells and almost completely blocked in cells at the plateau phase of growth.

The development of Na+-dependent binding of gamma-aminobutyric acid to particles of rat brain.

AbstractThe Na+‐dependent binding of γ‐aminobutyric acid (GABA) in rat cerebral hemispheres was studied by subcellular fractionation and double‐labelling procedures. The distributions of tracer amounts of [2,3‐3H] GABA and [U‐14C] surcrose acquired by P1 (crude nuclear) and P2 (synaptosomal, mitochondrial) particles during homogenization at O° C were compared in the presence of 40 mM Na+ and in the absence of added Na+. Results indicated that addition of Na+ to the homogenizing fluid promotes extra binding of GABA to both P1 and P2 particles and that these processes are age‐dependent, but different. GABA binding to P1 particles increased with age until 21‐22 days after which it remained rather constant. On the other hand, a more dramatic developmental change occurred in the binding of GABA to P2 fractions (which contain the majority of the nerve endings) which was maximal in the brains of rats 11 and 15 days old and which declined in older rats.

Het modern taalkundig concept van de intonatie-eenheid in de Laat Middeleeuws Griekse πολιτικος στιχος poëzie

In this article, I hope to strengthen the case that the study of so-called dead languages canbenefit from modern linguistic theory. More concretely, I show that we can apply themodem linguistic concept of the intonation unit, which is a theoretical notion fully developedon the basis of contemporary spoken (!) languages, to the Late Medieval Greekπολιτικος στιχος poetry (12th - 15th century). This type of poetry is conceptually made upof short, simple, "chunks" of information. More precisely, each verse consists of two(stylized) intonation units, demarcated by the fixed caesura, which can thus be equatedwith an Intonation Unit boundary. This thesis is supported by various arguments, both ofa metrical (e.g. avoidance of elision) and of a syntactico-semantic nature (e.g. position ofthe P2 particles).

Distribution of protein and nucleic acids in hyphae and microconidia of Fusarium.

Extracts obtained by manual grinding of the mycelium and microconidia of Fusarium oxysporum were fractionated into four particulate portions—designated P1, P2, P3 and P4—and into a soluble portion by differential centrifugation. Approximately 60% of the protein was recovered in the supernatant fraction whereas the ribonucleic acid content of the P3 and P4 particles was particularly high. The P4 particle fraction was composed of approximately 40% ribonucleic acid and 60% protein and contained a particle with a sedimentation constant of about 85 S. More than 70% of the deoxyribonucleic acid was recovered among the various particle types, but the deoxyribonucleic acid: protein ratio was highest in the P1 granules. Polysaccharides were particularly concentrated in the P3 fraction. On the basis of the distribution of bound hexosamine, the extracts appeared to be free of cell wall fragments. Several methods of disruption of the fungus hyphae were examined.