Actins from plant and animal sources tend not to form heteropolymers in vitro and function differently in plant cells

Summary. Pollen and skeletal muscle actins were purified and labeled with fluorescent dyes that have different emission wavelengths. Observation by electron microscopy shows that the fluorescent actins are capable to polymerize into filamentous actin in vitro, bind to myosin S-1 fragments, and have a critical concentration similar to unlabeled actin, indicating that they are functionally active. The globular actins from two sources were mixed and polymerized by the addition of ATP and salts. The copolymerization experiment shows that when excited by light of the appropriate wavelength, both red actin filaments (pollen actin) and green actin filaments (muscle actin) can be visualized under the microscope, but no filaments exhibiting both green and red colors are detected. Furthermore, coprecipitations of labeled pollen actin with unlabeled pollen and skeletal muscle actin were performed. Measurements of fluorescent intensity show that the amount of labeled pollen actin precipitating with pollen actin was much higher than that with skeletal muscle actin, indicating that pollen and muscle actin tend not to form heteropolymers. Injection of labeled pollen actin into living stamen hair cells results in the formation of normal actin filaments in transvacuolar strands and the cortical cytoplasm. In contrast, labeled skeletal muscle actin has detrimental effects on the cellular architecture. The results from coinjection of the actin-disrupting reagent cytochalasin D with pollen actin show that overexpression of pollen actin prolongs the displacement of the nucleus and facilitates the recovery of the nuclear position, actin filament architecture, and transvacuolar strands. However, muscle actin perturbs actin filaments when injected into stamen hair cells. Moreover, nuclear displacement occurs more rapidly when cytochalasin D and muscle actin are coinjected into the cell. It is concluded that actins from plant and animal sources behave differently in vitro and in vivo and that they are functionally not interchangeable.     

An assessment of some molecular parameters of mevalonate kinase from plant and animal sources

The molecular weights, diffusion coefficients, and sedimentation coefficients of mevalonate kinase in partially purified preparations from Hevea brasiliensis latex, Cucumis melo cotyledons, Phaseolus vulgaris cotyledons, bakers yeast, chicken liver, and rabbit liver have been determined by gel filtration in Sephadex G-100 and G-200 and by sucrose density gradient centrifugation. The enzyme had similar molecular weights (94800–103500), diffusion coefficients (5.39–5.62 × 10^?7 cm²/sec), and sedimentation coefficients (5.85–6.00 S) in the six preparations.     

Associations of like and unlike polysaccharides: Mechanism and specificity in galactomannans,interacting bacterial polysaccharides,and related systems

Chiroptical, rheological, and n.m.r.-relaxation evidence is presented, to identify interactions of two types between different polysaccharides: (1) mutual exclusion of incompatible molecules, with consequent increase in the effective concentration of both; and (2) energetically favourable association of structurally and sterically regular chain-segments. β-1,4-linked plant polysaccharides interact by association of unsubstituted backbone regions, either with like chians, or with sterically compatible, unlike molecules. Extracellular polysaccharides (xanthans) of Xanthomonas plant pathogens maintain their ordered native conformation in solution, and this accounts for their industrially valuable, rheological peculiarities. These materials bind strongly to the plant glycans. Random-coil bacterial gums show no such interactions, although dextran enhances autogelation of galactomannans by exclusion. Extracellular polysaccharides from Arthrobacter species also have ordered native conformations in solution, but do not share the specific interactions of xanthan. Native xanthan shows marked specificity in its interactions with plant glycans, indicating a possible biological role in host-pathogen recognition.     

Comparative subcellular distribution of apyrase from animal and plant sources. Characterization of microsomal apyrase

1. Apyrase (ATP: diphosphohydrolase) has been found in the microsomal fraction of rat salivary gland, mammary gland and uterus. 2. This enzyme, already described in plant tissue, is mainly present as a soluble polypeptide in tubers of Solanum tuberosum. 3. A fraction of this enzyme is associated with the microsomal fraction with a higher specific activity than the soluble one, for either ATP or ADP as substrate. 4. Apyrase bound to microsomes from rat and potato tissues was characterized in its substrate specificity and effect of inhibitors. 5. The Km values for ATP and ADP, optimum pH and metal ion requirement were determined. 6. A characteristic common to the microsomal and soluble apyrases is the stimulatory effect of a potato activator protein of soluble plant apyrase. 7. The microsomal-bound apyrase from rat and potato tissues were solubilized and subjected to size-exclusion chromatography. 8. The mammary gland and salivary gland apyrases eluted as molecular aggregates, in contrast to the uterus and potato enzyme.     

Conformational studies of bacterial polysaccharides. II. Optical activity of some bacterial capsular polysaccharides

The optical activity of the Klebsiella capsular polysaccharides of serotypes K1, K5, K6, K8, K11, K56, and K57 has been studied in aqueous solution. Measurements of ORD in the range 185–450 nm reveal anomalous ORD with Cotton effects near λ₀ = 195nm. The results are evaluated quantitatively according to hte Moffitt-Yang and the Drude equations. Straight lines are obtained in the Moffitt-Yang plots, while the corresponding Drude plots yield bent curves. The b₀ values, calculated from the slope of the stright lines in the Moffitt-Yang plot, range from 90 to 270 and suggest a helical superstructure for the capsular polysaccyharides. Positive b₀ values have been found for K1, K5, and K6 and negative b₀ values for K8, k11, K56, ad K57. Circular dichrosim has been mesured, but the CD curves are found to be truncated at the lower-wavelength end due to the 185-nm limit of the spectrometer used. Measurements of the temperature dependence of the specific optical rotation [α] reveal in all cases cooperative order–disorder transitions at temperatures, T_m, fro m298 to 323°K. The van′t Hoff enthalpies derived from the width of the transition curves are found to be similar in value to those of polypeptieds in aqueous solution. The K8 polysaccharide shows a two-step transition. The results are discussed in relation to the known primary structure and x-ray data from oriented and partially crystalline films. A model is suggested for the two-step transition in the K8 polysaccharide.     

The use of bacterial polysaccharides in bioprinting

Additive manufacturing or 3D printing has spearheaded a revolution in the biomedical sector allowing the rapid prototyping of medical devices. The recent advancements in bioprinting technology are enabling the development of potential new therapeutic options with respect to tissue engineering and regenerative medicines. Bacterial polysaccharides have been shown to be a central component of the inks used in a variety of bioprinting processes influencing their key features such as the mechanical and thermal properties, printability, biocompatibility, and biodegradability. However, the implantation of any foreign structure in the body comes with an increased risk of bacterial infection and immunogenicity. In recent years, this risk is being potentiated by the rise in nosocomial multidrug-resistant bacterial infections. Inks used in bioprinting are being augmented with antimicrobials to mitigate this risk. The applications of bacterial polysaccharide-based bioinks have the potential to act as a key battlefront in the war against antibiotic resistance. This paper reviews the range of bacterial polysaccharides used in bioprinting and discusses the potential of various bioactive polysaccharides to be integrated into these inks.     

Enzymatic modification of plant polysaccharides

Enzymes find widespread industrial use in the modification of the functional properties of plant polysaccharides both in vivo and in vitro. Reactions catalysed include depolymerization, debranching and de-esterification, depending on the specific enzyme or enzyme mixture employed and on the particular industrial requirement. Depolymerization of pentosans and/or barley β-glucans to destroy their viscosity-building properties is essential in starch and gluten manufacture, in the mashign of barley malt and in the production of maltosaccharide syrups. Depolymerization of pectin is required in juice clarification and to allow concentration. However, in other instances the aim may be to maintain or, at most, only slightly alter the molecular size of functional polysaccharides, i.e. in the conversion of guar galactomannan to a locust-bean type galactomannan and in the enzymic treatment of wheat-flour doughs. Enzymes may also be used to produce specific oligosaccharide fragments from polysaccharides and as diagnostic tools in the measurement of a particular polysaccharide in a mixture.     

Uptake of metals by bacterial polysaccharides

J.L. GEDDIE AND I.W. SUTHERLAND. 1993. The binding of cations by a range of bacterial polysaccharides was examined. Comparison of native and deacetylated polymers indicated the influence of polysaccharide acetylation on ion uptake and selectivity. The effects of temperature and pH on ion uptake were also examined. Metal ion uptake was carried out by dialysis and samples were analysed using ion chromatography. The native acetylated polymers showed a selectivity for Ca²⁺ > Mg²⁺ > monovalent cations, whereas samples lacking acetyl groups showed a selectivity for monovalent cations > Mg²⁺ > Ca²⁺. Increased temperatures reduced the capacity for several of the polymers to bind the cations; The Zoogloea ramigera polymer appeared least affected. The pH value also affected uptake.     

Ferritins, bacterial virulence and plant defence

The enterobacterial pathogen Erwinia chrysanthemi causes soft rot diseases on a wide range of plants, including the model plant Arabidopsis thaliana. This bacterium proliferates in the host by secreting a set of pectin degrading enzymes responsible for symptom development. In addition, survival of this bacterium in planta requires two high-affinity iron acquisition systems mediated by siderophores and protective systems against oxidative damages, suggesting the implication by both partners of accurate mechanisms controlling their iron homeostasis under conditions of infection. In this review, we address this question and we show that ferritins both from the pathogen and the host are subtly implicated in the control of this interplay.     

Heterogeneity in bacterial surface polysaccharides,probed on a single-molecule basis

The heterogeneity in bacterial surface macromolecules was probed by examining individual macromolecules on the surface of Pseudomonas putida KT2442 via single-molecule force spectroscopy (SMFS). Using an atomic force microscope (AFM), the silicon nitride tip was brought into contact with biopolymer molecules on bacterial cells and these macromolecules were stretched. Force-extension measurements on different bacterial cells showed a range of adhesion affinities and polymer lengths. However, substantial heterogeneity was also observed in the force-extension curves on a single bacterium. A given bacterium has biopolymers that range in size from tens to hundreds of nanometers, with adhesion affinities for the AFM tip from nearly zero to greater than 1 nN. A distribution of polymer sizes was confirmed by size-exclusion chromatography. The freely jointed chain (FJC) model for polymer elasticity was applied to individual force-extension curves in order to estimate the contour lengths and segment lengths of the polymer chains. A range of segment lengths was obtained using the FJC model, from 0.154-0.45 nm in water, 0.154-0.32 nm in 0.01 M KCl, and 0.154-0.65 nm in 0.1 M KCl. The modeling confirms that the heterogeneity in biopolymers is more than a matter of differences in molecular weights, since a range of stiffnesses (segment lengths) was also observed. The effect of salt concentration on biopolymer conformation and adhesion was also explored. While the biopolymers were flexible in all solvents, they were slightly more extended in water than in either of the salt solutions (0.01 and 0.1 M KCl). The adhesion of polysaccharides with the AFM tip was not dependent on salt concentration, because the polymers were not highly charged and heterogeneity overwhelmed any trends that could be observed in adhesion with respect to solution ionic strength. These experiments indicate that heterogeneity in biopolymer properties on an individual bacterium and within a population of bacterial cells may be much greater than previously believed and should be incorporated into models of bacterial adhesion.     

细菌荚膜多糖的化学结构

荚膜是一些细菌所具有的表层结构,与多种疾病有着密切联系。细菌荚膜多糖不仅结构复杂,而且在免疫活性方面发挥着重要的作用。同一种细菌根据其荚膜多糖的抗原性不同可分为不同的血清型,不同血清型细菌荚膜多糖的化学结构也存在差异。以荚膜多糖为基础的疫苗正在积极研究开发当中,对不同致病细菌荚膜多糖具体化学结构的掌握是疫苗得到许可的必备条件之一。本文对致病细菌荚膜多糖的化学结构进行了归纳和总结,以期为荚膜多糖的化学结构研究和疫苗开发提供参考。     

Antibody recognition of bacterial surfaces and extracellular polysaccharides

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