Dynamic distribution of BIMG(PP1) in living hyphae of Aspergillus indicates a novel role in septum formation

Mutation of bimG, the major protein phosphatase 1 gene in Aspergillus nidulans, causes multiple cell cycle and hyphal growth defects that are associated with overphosphorylation of subcellular components. We have used functional translational fusions with the green fluorescent protein (GFP) to show that BIMG has at least four discrete locations within growing hyphae. Three of these locations, the hyphal tip, the spindle pole body and the nucleus, correlate with previously known requirements for bimG(PP1) in mitosis and hyphal growth and are highly dynamic. BIMG-GFP in the hyphal tip seemed to be associated with the plasma membrane and formed a collar of fluorescence within the apical dome. The distribution of nuclear BIMG-GFP varied depending on nutritional conditions; on poor medium, it concentrated more in the nucleolus than in the nucleoplasm, whereas on rich medium, it was more evenly distributed between the two nuclear regions. The association of BIMG-GFP with developing septa was transient, and we present evidence that BIMG phosphatase plays a direct role in septum formation, distinct from its role in mitosis. We conclude that, by being physically present at several sites, the BIMG phosphatase has roles in multiple cellular processes.

Characterization of a cell-wall acid phosphatase (PhoAp) in Aspergillus fumigatus

In the filamentous fungus Aspergillus fumigatus, the vast majority of the cell-wall-associated proteins are secreted proteins that are in transit in the cell wall. These proteins can be solubilized by detergents and reducing agents. Incubation of a SDS/beta-mercaptoethanol-treated cell-wall extract with various recombinant enzymes that hydrolyse cell-wall polysaccharides resulted in the release of a unique protein in minute amounts only after incubation of the cell wall in the presence of 1,3-beta-glucanase. Sequence analysis and biochemical studies showed that this glycoprotein, with an apparent molecular mass of 80 kDa, was an acid phosphatase (PhoAp) that was active on both phosphate monoesters and phosphate diesters. PhoAp is a glycosylphosphatidylinositol-anchored protein that was recovered in the culture filtrate and cell-wall fraction of A. fumigatus after cleavage of its anchor. It is also a phosphate-repressible acid phosphatase. The absence of PhoAp from a phosphate-rich medium was not associated with a reduction in fungal growth, indicating that this cell-wall-associated protein does not play a role in the morphogenesis of A. fumigatus.

Relationship of growth cessation with the formation of diferulate cross-links and p-coumaroylated lignins in tall fescue leaf blades

We examined relationships among cell wall feruloylation, diferulate cross-linking, p-coumarate deposition, and apoplastic peroxidase (EC 1.11.1.7) activity with changes in the elongation rate of leaf blades of slow and rapid elongating genotypes of tall fescue ( Festuca arundinacea Schreb.). Growth was not directly influenced by ferulic acid deposition but leaf elongation decelerated as 8-5-, 8- O-4-, 8-8-, and 5-5-coupled diferulic acids accumulated in cell walls. Growth rapidly slowed and stopped with the deposition of p-coumarate, which is primarily associated with lignification in grass cell walls. Accretion of ferulate, diferulates and p-coumarate continued after growth ended, into the later stages of secondary wall formation. The concentration of 8-coupled diferulates dwarfed that of the more commonly measured 5-5-coupled isomer, suggesting that the latter dimer is a poor indicator of diferulate cross-linking in cell walls. Further work is required to clearly demonstrate the role of diferulate cross-linking and p-coumaroylated lignins in the cessation of leaf growth in grasses.

Legumains and their functions in plants

Legumains are a family of plant and animal Asn-specific cysteine proteinases with extra-cytoplasmic localization in vacuoles or cell walls. Plant legumains are involved in Asn-specific propolypeptide processing during, for example, storage-protein deposition in maturing seeds, when these proteins are resistant against degradation by legumains. With the transition to germination and subsequent seedling growth, storage proteins are opened to unlimited cleavage by legumains, which now contribute to protein mobilization. Here, we suggest a hypothesis that unifies both functions of legumains. Their action as propolypeptide-processing or protein-degrading enzymes is naturally controlled by the conformational state of their substrates, which undergo development- or environment-dependent changes. The suggested substrate conformation-dependent differential roles of legumains might not be restricted to seeds but could also apply to cells of different tissues in vegetative organs.

Recombinant Lactobacillus johnsonii as a mucosal vaccine delivery vehicle

Lactobacilli are considered to be safe organisms making them attractive as vehicles for oral vaccination. We report that Lactobacillus johnsonii (Lj) partially survived simulated gastric conditions in vitro, suggesting that it could be used as an oral vaccine delivery vehicle. In order to test this approach, we used the cell wall anchored proteinase PrtB, isolated from Lactobacillus delbrueckii subsp. bulgaricus as a model antigen. Using a new vector system, we demonstrated expression of both proteinase PrtB alone and a mimotope peptide derived from tetanus toxin integrated in the sequence of proteinase PrtB (TTmim-PrtB fusion protein) on the surface of Lj. Oral immunisation of mice with recombinant Lj, expressing the TTmim-PrtB fusion protein induced a systemic IgG response against Lj and recombinantly expressed proteinase PrtB but no antibody response against the tetanus toxin mimotope suggesting that the mimotope was not sufficiently immunogenic to induce an immune response. Interestingly, a proteinase PrtB specific fecal IgA response was also induced, indicating that the proteinase PrtB fusion protein expressed as a cell surface protein on Lj can induce both systemic and local mucosal immune responses.

[The cell wall-degrading activities of lysin encoded by chlorella virus PBCV-1]

Lysin was isolated from Chlorella NC64A lysate which was infected by Chlorella virus PBCV-1. The enzyme property detection of lysin shows that it contains at least three enzyme activities: chitinase, chitosanase and beta-1, 3-Glucanase. This is consistent with the compose of Chlolrella cell wall. Chitinase and chitosanase, especially chitinase plays a important role in the process of virus entry. One 52 kD chitinase, one 56 kD chitosanase and one 36 kD chitosanase were obtained after purified by FPLC.

Structure, physicochemical properties and in vitro fermentation of enzymatically degraded cell wall materials from apples

Cell wall materials (CWM) prepared from apple parenchyma tissue by treatment with commercial enzymes for maceration, mash fermentation and liquefaction were characterised with regard to their composition and structure as well as their physicochemical and physiological properties. Increasing enzymatic degradation of the CWM resulted in growing loss of the pectin matrix, decreasing porosity as well as increasing particle aggregation. Due to these structural alterations the water binding, the viscoelastic properties of the CWM-water-suspensions and the in vitro fermentation, forming short chain fatty acids, were reduced. The investigations showed that interrelations exist between enzymatic treatment and changes of (i) structure and state of matrices (evaluated by means of thermal analysis), (ii) physicochemical properties and (iii) physiological properties. So the application of liquefying enzymes can lead to a complete removal of the pectin matrix, causing an essentially improved thermal stability of the CWM preparation, but strongly reduced water binding and reduced structure-forming properties into the CWM-water-suspensions. The formation of short-chain fatty acids during in vitro fermentation of the CWM preparations by fresh human faeces flora depended on the portion and the state of the pectin matrix and the cellulose network, respectively.

The use of trypsin to solubilize wall proteins from Candida albicans led to the identification of chitinase 2 as an enzyme covalently linked to the yeast wall structure

The use of trypsin to break proteins covalently linked to the yeast walls of Candida albicans released approx. 50% of the proteins, but also glucose and N-acetylglucosamine. Analysis by affinity chromatography indicated that glucose and/or N-acetylglucosamine formed part of the same supramolecular complexes with mannoproteins. These complexes would represent a new type of cell wall structuration in which beta-1,6 glucan and chitin are linked to proteins. An internal peptide from a 50-kDa protein released by trypsin was sequenced, showing 100% identity with chitinase 2 protein and 92% with chitinase 3. The electrophoretic mobility of the chitinase 2 protein was changed by treatment with EndoH or beta-elimination, indicating that the enzyme was both N- and O-mannosylated.

Metabolic engineering of the morphology of Aspergillus oryzae by altering chitin synthesis

Morphology and alpha-amylase production during submerged cultivation were examined in a wild-type strain (A1560) and in strains of Aspergillus oryzae in which chitin synthase B (chsB) and chitin synthesis myosin A (csmA) have been disrupted (ChsB/G and CM101). In a flowthrough cell, the growth of submerged hyphal elements was studied online, making it possible to examine the growth kinetics of the three strains. The average tip extension rates of the CM101 and ChsB/G strains were 25 and 88% lower, respectively, than that of the wild type. The branching intensity in the CM101 strain was 25% lower than that in the wild type, whereas that in the ChsB/G strain was 188% higher. During batch cultivation, inseparable clumps were formed in the wild-type strain, while no or fewer large inseparable clumps existed in the cultivations of the ChsB/G and CM101 strains. The alpha-amylase productivity was not significantly different in the three strains. A strain in which the transcription of chsB could be controlled by the nitrogen source-regulated promoter niiA (NiiA1) was examined during chemostat cultivation, and it was found that the branching intensity could be regulated by regulating the promoter, signifying an important role for chsB in branching. However, the pattern of branching responded very slowly to the change in transcription, and increased branching did not affect alpha-amylase productivity. alpha-Amylase residing in the cell wall was stained by immunofluorescence, and the relationship between tip number and enzyme secretion is discussed.

Cell wall invertase in developing rice caryopsis: molecular cloning of OsCIN1 and analysis of its expression in relation to its role in grain filling

To establish the significance of cell wall invertase in grain filling of rice (Oryza sativa L.), we cloned a cDNA for a cell wall invertase from developing grains of rice. The cDNA, designated OsCIN1, contains an open reading frame of 1731 bp encoding a polypeptide of 577 amino acid residues. The deduced amino acid sequence showed typical features of the cell wall invertases, including a beta-fructosidase motif and a cysteine catalytic site, and shared 78.6 and 73.7% identity with maize cell wall invertases, Incw1 and Incw2, respectively. OsCIN1 is expressed in roots, in sink- and source-leaves, and in panicles. During the course of grain filling in the caryopses, OsCIN1 transcript is detectable only in the very early stage of their development, 1-4 d after flowering, when the cell wall invertase activity is the highest and the increase in caryopsis length is rapid. In situ localization of the mRNA revealed that OsCIN1 is expressed preferentially in the vascular parenchyma of the dorsal vein, integument and its surrounding cells, and is expressed weakly in the nucellar projection and nucellar epidermis. These results suggest that, during the early stage of caryopsis development, OsCIN1 is important for supplying a carbon source to developing filial tissues by cleaving unloaded sucrose in the apoplast.

Hypergravity-induced increase in the apoplastic pH and its possible involvement in suppression of beta-glucan breakdown in maize seedlings

Elongation growth of both coleoptiles and mesocotyls of maize (Zea mays L. cv. Cross Bantam T51) seedlings was inhibited under basipetal hypergravity (300 g) conditions. Hypergravity increased the pH of the apoplastic fluid of coleoptiles from 5.0 to 5.5 and mesocotyls from 5.2 to 5.7. When beta-1,3:1,4-D-glucanases (beta-glucanases) extracted from cell walls of the 1-g control coleoptiles and mesocotyls were assayed at pH 5.0 and 5.5 for coleoptiles, and at 5.2 and 5.7 for mesocotyls, respectively, the activity in the increased pH conditions was significantly lower than that in the control pH conditions. During the autolysis of the enzymically active cell wall preparations obtained from 1-g control organs, a molecular mass downshift of hemicellulosic polysaccharides occurred in cell walls. This downshift was suppressed in the increased pH conditions as compared with the control pH conditions. It was reported that hypergravity increased the molecular mass of hemicellulosic polysaccharides by decreasing the beta-glucanase activity, and thereby decreased the mechanical extensibility of cell walls in maize coleoptiles and mesocotyls. These results suggest that, in maize coleoptiles and mesocotyls, hypergravity-induced increase in the pH in the apoplastic fluid is involved in the reduction of the activity of beta-glucanases which, in turn, causes an increase in the molecular mass of hemicellulosic polysaccharides and inhibits elongation growth.

Hydrolytic activity and ultrastructural changes in fruit skins from two prickly pear (Opuntia sp.) varieties during storage

The activity of four cell wall hydrolases, pectinmethylesterase (PME), polygalacturonase (PG), cellulase, and beta-galactosidase (beta-Gal), was measured in fruit skins of two prickly pear varieties, Naranjona and Charola, during storage at 18 degrees C and 85-95% relative humidity (RH). In Naranjona (Opuntia ficus indica), of short postharvest life (ca. 2 weeks), PG, cellulase, and beta-Gal increased their activity more than twice, whereas PME activity tended to increase only slightly during storage. In Charola (Opuntia sp.), of long postharvest life (ca. 2 months), only beta-Gal increased its activity (77%), showing a high PG activity from the beginning of storage. Transmission electron microscopy observations showed middle lamella dissolution at the end of storage for both varieties. Naranjona showed a higher cell wall enzymatic activity than Charola, in agreement with their storability differences. Our results suggest that PG and cellulase in Naranjona and PG and beta-Gal in Charola are the main enzymes responsible for cell wall hydrolytic and ultrastructural changes in skins of stored prickly pears.

The activity of a developmentally regulated cysteine proteinase is required for cyst wall formation in the primitive eukaryote Giardia lamblia

Giardia is an intestinal parasite that belongs to the earliest diverging branch of the eukaryotic lineage of descent. Giardia undergoes adaptation for survival outside the host's intestine by differentiating into infective cysts. Encystation involves the synthesis and transport of cyst wall constituents to the plasma membrane for release and extracellular organization. Nevertheless, little is known about the molecular events related to cyst wall biogenesis in Giardia. Among the components of the cyst wall there are two proteins that we have previously identified and characterized: CWP1 (26 kDa) and CWP2 (39 kDa). Expression of these proteins is coordinately induced, and both concentrated within encystation-specific secretory vesicles before their extracellular polymerization. Although highly similar to each other at the amino terminus, CWP2 includes a COOH-terminal 121-amino acid extension. Here, we show that this extension, rich in basic residues, is cleaved from CWP2 before cyst wall formation by an intracellular cysteine proteinase activity, which is induced during encystation like CWPs. Specific inhibitors prevent release of cyst wall materials, abolishing cyst wall formation. We also report the purification, cloning, and characterization of the encystation-specific cysteine proteinase responsible for the proteolytic processing of CWP2, which is homologue to lysosomal cathepsin C. Encystation-specific cysteine proteinase ESCP possesses unique characteristics compared with cathepsins from higher eukaryotes, such as a transmembrane domain and a short cytoplasmic tail. These features make this enzyme the most divergent cathepsin C identified to date and provide new insights regarding cyst wall formation in Giardia.

Submergence research using Rumex palustris as a model; looking back and going forward

Flooding is a phenomenon that destroys many crops worldwide. During evolution several plant species evolved specialized mechanisms to survive short- or long-term waterlogging and even complete submergence. One of the plant species that evolved such a mechanism is Rumex palustris. When flooded, this plant species is capable to elongate its petioles to reach the surface of the water. Thereby it restores normal gas exchange which leads to a better survival rate. Enhanced levels of ethylene, due to physical entrapment, is the key signal for the plant that its environment has changed from air to water. Subsequently, a signal transduction cascade involving at least four (classical) plant hormones, ethylene, auxin, abscisic acid, and gibberellic acid, is activated. This results in hyponastic growth of the leaves accompanied by a strongly enhanced elongation rate of the petioles enabling them to reach the surface. Other factors, among them cell wall loosening enzymes have been shown to play a role as well.

Detection and localization of pectin methylesterase isoforms in pollen tubes of Nicotiana tabacum L

Pectin methylesterases (PMEs) were detected in tobacco ( Nicotiana tabacum) pollen tubes grown in vitro. Seven PME isoforms exhibiting a wide isoelectric-point (pI) range (5.3-9.1) were found in crude extracts of pollen tubes. These isoforms were mainly retrieved in supernatants after low- and high-speed separation of the crude extract. Two isoforms, with pIs 5.5 and 7.3 and molecular weight about 158 kDa, were detected by immunoblotting with anti-flax PME antiserum. Localization of pectins and PME isoforms in pollen tubes was investigated by immunogold labelling with JIM5 monoclonal antibodies and anti-flax PME antiserum, respectively. In germinated pollen grains, two PME isoforms were mainly detected in the exine, Golgi apparatus and secretory vesicles. In pollen tubes the same two PME isoforms were distributed along the outer face of the plasma membrane in the vicinity of the inner layer of the cell wall, in the Golgi and around secretory vesicles. In pollen grains, PME isoforms were, in some cases, mixed with acidic pectins in proximity to the outer surface of the plasma membrane. In pollen tubes the presence of PMEs inside secretory vesicles carrying esterified pectins supports the hypothesis that, during pollen tube growth, PMEs could be transferred by secretory vesicles in a precursor form and be activated at the tip where exocytosis takes place.

Specialized peptidoglycan of the bacterial endospore: the inner wall of the lockbox

A modified peptidoglycan (PG) wall is required for maintenance of spore core dehydration and the accompanying metabolic dormancy and heat resistance. Production of the spore PG depends on the cooperative expression of gene products within both the mother cell and forespore compartments of the sporangium. Structural elements that differentiate spore PG from vegetative cell PG include the presence of the modified sugar muramic-delta-lactam and a low level of peptide cross-links between the glycan strands. Detailed analyses of PG structure in dormant spores and in developing forespores of wild-type and mutant strains are providing data on factors required for introduction of these modifications and the importance of these structural elements in determining spore properties. Muramic-delta-lactam is not required for spore core dehydration but serves as a specificity factor for spore germination lytic enzymes. Cross-linking of spore PG can vary over a relatively wide range without significantly effecting spore core dehydration but does have an influence on the rate of spore germination and outgrowth. Future studies will examine how the two cells within the sporangium coordinate the production of this unique structure between themselves and how specific spore PG structural modifications are produced and participate in determining spore resistance properties.

Organization of cell walls in Sandersonia aurantiaca floral tissue

Visual symptoms of the onset of senescence in Sandersonia aurantiaca flowers begin with fading of flower colour and wilting of the tissue. When fully senescent, the flowers form a papery shell that remains attached to the plant. The cell walls of these flowers have been examined to determine whether there are wall modifications associated with the late stages of expansion and subsequent senescence-related wilting. Changes in the average molecular size of pectin were limited through flower opening and senescence, although there was a loss of neutral sugar-containing side-branches from pectins in opening flowers, and the total amounts of pectin and cellulose continued to rise in cell walls of fully senescent sandersonia flowers. Xyloglucan endotransglycosylase activity increased in opening and mature flowers, but declined sharply as flowers wilted. Concomitantly, the proportion of hemicellulose polymers of increasing molecular weight increased from flower expansion up to the point at which wilting occurred. Approximately 50% of the non-cellulosic neutral sugar in mature flower cell walls was galactose, primarily located in an insoluble cell wall fraction. Total galactose in this fraction increased per flower with maturity, then declined at the onset of wilting. Beta-galactosidase activity was low in expanding tepals, but increased as flowers matured and wilted.

Spore germination

Despite being relatively insensitive to environmental insult, the spore is responsive to low concentrations of chemical germinants, which induce germination. The process of bacterial spore germination involves membrane permeability changes, ion fluxes and the activation of enzymes that degrade the outer layers of the spore. A number of components in the spore that are required for the germination response have been identified, including a spore-specific family of receptor proteins (the GerA family), an ion transporter and cortex lytic enzymes. The germinant traverses the outer layers of the spore and interacts with its receptor in the inner membrane to initiate the cascade of germination events, but the molecular details of this signal transduction process remain to be identified.

A role for arabinogalactan proteins in gibberellin-induced alpha-amylase production in barley aleurone cells

Arabinogalactan proteins (AGPs) are plant proteoglycans that have been implicated in plant growth and development. The possible involvement of AGPs in the action of gibberellin (GA), a class of plant hormones, was examined by applying beta-glucosyl Yariv reagent (beta-Glc)3Y, a synthetic phenyl glycoside that interacts selectively with AGPs, to barley aleurone protoplasts. Gibberellin induces transcription and secretion of alpha-amylases in the protoplasts. Induction of alpha-amylase was clearly inhibited by (beta-Glc)3Y but not by (alpha-Gal)3Y, a negative control of the Yariv reagent that does not interact with AGPs. Transfection analysis, using an alpha-amylase promoter-GUS fusion gene in the protoplasts, indicated that the transcriptional activation of the alpha-amylase promoter was inhibited specifically by (beta-Glc)3Y. These observations are the first indication of an involvement of AGPs in a plant hormone function. The inhibitory effect of (beta-Glc)3Y was not observed when aleurone layers or half-seed grains were used. This result, together with the fact that protoplasts do not have cell walls, suggests that the AGPs that function in alpha-amylase induction reside at the plasma membrane. An aleurone-specific AGP was detected by reversed-phase HPLC, and supported the idea that an AGP may play an important role in aleurone-specific events. The possible mechanism of AGP function in gibberellin-induced alpha-amylase production is discussed.

Improving selenium extraction by sequential enzymatic processes for Se-speciation of selenium-enriched Agaricus bisporus

Sample preparation methods based on the use of proteolytic and cell wall digesting enzymes for the speciation analysis of selenized mushroom were investigated. The sample (Agaricus bisporus; 160 microg total Se per g sample) was grown on compost supplemented with selenized yeast. Experiments were carried out to elucidate the possible role of the cell wall digesting enzymes--Lysing enzyme and Driselase--in the improvement of extraction efficiency with and without inhibiting proteolysis during cell wall digestion. A 3-step procedure applying Lysing enzyme and pronase gave the highest extraction efficiency (89%); however, the best species recovery was achieved by a one-step proteolytic procedure. All the procedures of selenium speciation were controlled by independent ICP-AES analysis measuring the total amount of selenium.

The pathobiology of Paracoccidioides brasiliensis

Paracoccidioides brasiliensis causes one of the most prevalent systemic mycoses in Latin America--paracoccidioidomycosis. It is a dimorphic fungus that undergoes a complex transformation in vivo, with mycelia in the environment producing conidia, which probably act as infectious propagules upon inhalation into the lungs, where they transform to the pathogenic yeast form. This transition is readily induced in vitro by temperature changes, resulting in modulation of the composition of the cell wall. Notably, the polymer linkages change from beta-glucan to alpha-glucan, possibly to avoid beta-glucan triggering the inflammatory response. Mammalian oestrogens inhibit this transition, giving rise to a higher incidence of disease in males. Furthermore, the susceptibility of individuals to paracoccidioidomycosis has a genetic basis, which results in a depressed cellular immune response in susceptible patients; resistance is conferred by cytokine-stimulated granuloma formation and nitric oxide production. The latency period and persistence of the disease and the apparent lack of efficacy of humoral immunity are consistent with P. brasiliensis existing as a facultative intracellular pathogen.

The antibacterial properties of secreted phospholipases A2: a major physiological role for the group IIA enzyme that depends on the very high pI of the enzyme to allow penetration of the bacterial cell wall

The antibacterial properties of human group IIA secreted phospholipase A(2) against Gram-positive bacteria as a result of membrane hydrolysis have been reported. Using Micrococcus luteus as a model system, we demonstrate the very high specificity of this human enzyme for such hydrolysis compared with the group IB, IIE, IIF, V, and X human secreted phospholipase A(2)s. A unique feature of the group IIA enzyme is its very high pI due to a large excess of cationic residues on the enzyme surface. The importance of this global positive charge in bacterial cell membrane hydrolysis and bacterial killing has been examined using charge reversal mutagenesis. The global positive charge on the enzyme surface allows penetration through the bacterial cell wall, thus allowing access of this enzyme to the cell membrane. Reduced bacterial killing was associated with the loss of positive charge and reduced cell membrane hydrolysis. All mutants were highly effective in hydrolyzing the bacterial membrane of cells in which the cell wall was permeabilized with lysozyme. These same overall characteristics were also seen with suspensions of Staphylococcus aureus and Listeria innocua, where cell membrane hydrolysis and antibacterial activity of human group IIA enzyme was also lost as a result of charge reversal mutagenesis.