The Role of Glucosidase I (Cwh41p) in the Biosynthesis of Cell Wall β-1,6-Glucan Is Indirect

CWH41, a gene involved in the assembly of cell wall β-1,6-glucan, has recently been shown to be the structural gene for Saccharomyces cerevisiae glucosidase I that is responsible for initiating the trimming of terminal α-1,2-glucose residue in the N-glycan processing pathway. To distinguish between a direct or indirect role of Cwh41p in the biosynthesis of β-1,6-glucan, we constructed a double mutant, alg5Δ (lacking dolichol-P-glucose synthase) cwh41Δ, and found that it has the same phenotype as the alg5Δ single mutant. It contains wild-type levels of cell wall β-1,6-glucan, shows moderate underglycosylation of N-linked glycoproteins, and grows at concentrations of Calcofluor White (which interferes with cell wall assembly) that are lethal to cwh41Δ single mutant. The strong genetic interactions of CWH41 with KRE6 and KRE1, two other genes involved in the β-1,6-glucan biosynthetic pathway, disappear in the absence of dolichol-P-glucose synthase (alg5Δ). The triple mutant alg5Δcwh41Δkre6Δ is viable, whereas the double mutant cwh41Δkre6Δ in the same genetic background is not. The severe slow growth phenotype and 75% reduction in cell wall β-1,6-glucan, characteristic of the cwh41Δkre1Δ double mutant, are not observed in the triple mutant alg5Δcwh41Δkre1Δ. Kre6p, a putative Golgi glucan synthase, is unstable in cwh41Δ strains, and its overexpression renders these cells Calcofluor White resistant. These results demonstrate that the role of glucosidase I (Cwh41p) in the biosynthesis of cell wall β-1,6-glucan is indirect and that dolichol-P-glucose is not an intermediate in this pathway.

Effect of cell wall properties of plant tissue on porosity and shrinkage of dried apple

In this study cell wall properties; moisture distribution, stiffness, thickness and cell dimension have been taken into consideration. Cell wall stiffness dependent on complex combination of plant cell microstructures, composition and water holding capacity of the cell. In this work, some preliminary steps taken by investing cell wall properties of apple in order to predict change of porosity and shrinkage during drying. Two different types of apple cell wall characteristic were investigated to correlate with porosity and shrinkage after convective drying. A scanning electron microscope (SEM), 2N Intron, a pyncometer and image J software were used in order to measure and analyze cell characteristics, water dynamics, porosity and shrinkage. Cell stiffness of red delicious apple was found higher than granny smith apples. A significant relationship has found between cell wall characteristics and both heat and mass transfer. Consequently, evolution of porosity and shrinkage noticeably influenced during convective drying by the nature of cell wall. This study has brought better understanding of porosity and shrinkage of dried food stuff in microscopic (cell) level and would provide better insight to attain energy effective drying process and quality food stuff.

Characterisation of a cell wall-anchored protein of Staphylococcus saprophyticus associated with linoleic acid resistance

The Gram-positive bacterium Staphylococcus saprophyticus is the second most frequent causative agent of community-acquired urinary tract infections (UTI), accounting for up to 20% of cases. A common feature of staphylococci is colonisation of the human skin. This involves survival against innate immune defenses including antibacterial unsaturated free fatty acids such as linoleic acid which act by disrupting bacterial cell membranes. Indeed, S. saprophyticus UTI is usually preceded by perineal skin colonisation.

Effect of cell wall properties on porosity and shrinkage of dried apple

Water removal during drying depends on the pathway of water migration from food materials. Moreover, the water removal rate also depends on the characteristics of the cell wall of plant tissue. In this study, the influence of cell wall properties (such as moisture distribution, stiffness, thickness and cell dimension) on porosity and shrinkage of dried product was investigated. Cell wall stiffness depends on a complex combination of plant cell microstructure, composition of food materials and the water-holding capacity of the cell. In this work, a preliminary investigation of the cell wall properties of apple was conducted in order to predict changes of porosity and shrinkage during drying. Cell wall characteristics of two types of apple (Granny Smith and Red Delicious) were investigated under convective drying to correlate with porosity and shrinkage. A scanning electron microscope (SEM), 2kN Intron, pycnometer and ImageJ software were used in order to measure and analyse cell characteristics, water holding capacity of cell walls, porosity and shrinkage. The cell firmness of the Red Delicious apple was found to be higher than for Granny Smith apples. A remarkable relationship was observed between cell wall characteristics when compare with heat and mass transfer characteristics. It was also found that the evolution of porosity and shrinkage are noticeably influenced by the nature of the cell wall during convective drying. This study has revealed a better understanding of porosity and the shrinkage of dried food at microscopy (cell) level, and will provide better insights to attain energy-effective drying processes and improved quality of dried foods.

Trehalose toxicity in cuscuta-reflexa - cell-wall synthesis is inhibited upon trehalose feeding

a,a-Trehalose induced a rapid blackening of the terminal 2.5-centimete region of excised Cuscuta relexa Roxb. vine. The incorporation of radioactivite from [I'C]glucose into alkali-insoluble fraction of shoot tip was markedly inhibited by 12 hours of trehalose feeding to an excised vine. This inhibition was confied to the apical segment of the vine in which cell elongation occurred. The rate of blackening of shoot tip explants was hastened by the addition of gibberellic acid A3, which promoted elongationgrowth of isolated Cuscuta shoot tips. The symptom of trehalose toxicity was duplicated by 2-deoxygucose, which has been shown to ba potent inhibitor of ceD wall synthesis in yeast. The observations suggest that trehalose interferes with the synthesis of ceDl wail polysaccharides, the chief component of which was presumed to be cellulose.

Binding of polyphenols to plant cell wall analogues - Part 1: Anthocyanins

Anthocyanins are located within the vacuole of plant cells, and are released following cell rupture during eating or processing at which time they first come into contact with the plant cell wall. The extent of anthocyanin-cell wall interaction was investigated by monitoring the rate of anthocyanin depletion in the presence of pure cellulose or cellulose-pectin composites as cell wall models. It was found that anthocyanins interact with both cellulose and pectin over a two-stage process with initially (mins-hours) 13 similar to 18% of anthocyanins binding to cellulose or cellulose/pectincomposites. With prolonged exposure (days-weeks), a gradual increase in anthocyanin binding occurs, possibly due to anthocyanins stacking on top of a base layer. Binding of acylated and non-acylated anthocyanins followed a similar pattern with slightly more (5-10%) binding of the acylated forms. Composites with the highest pectin content had the greatest anthocyanin binding suggesting the existence of both ionic interactions (with pectin) and hydrophobic interactions (with cellulose) of anthocyanin with plant cell walls.

Binding of polyphenols to plant cell wall analogues - Part 2: Phenolic acids

Bacterial cellulose and cellulose-pectin composites were used as well-defined model plant cell wall (PCW) systems to study the interaction between phenolic acids (PA) derived from purple carrot juice concentrate (PCJC) and PCW components. Significant PA depletion from solution occurred, with pure cellulose initially (30 s-1 h) absorbing more than cellulose-pectin composites in the first hour (ca 20% cf 10-15%), but with all composites absorbing similar levels (ca 30%) after several days. Individual PAs bound to different relative extents with caffeic acid > chlorogenic acid > ferulic acid. Extrapolation of data for these model systems to carrot puree suggests that nutritionally-significant amounts of PAs could bind to cell walls, potentially restricting bioavailability in the small intestine and, as a consequence, delivering PAs to the large intestine for fermentation and metabolism by gut bacteria. (C) 2012 Elsevier Ltd. All rights reserved.

Non-cellulosic cell wall polysaccharides are subject to genotype × environment effects in sorghum (Sorghum bicolor) grain

Sorghum is a staple food for half a billion people and, through growth on marginal land with minimal inputs, is an important source of feed, forage and increasingly, biofuel feedstock. Here we present information about non-cellulosic cell wall polysaccharides in a diverse set of cultivated and wild Sorghum bicolor grains. Sorghum grain contains predominantly starch (64–76) but is relatively deficient in other polysaccharides present in wheat, oats and barley. Despite overall low quantities, sorghum germplasm exhibited a remarkable range in polysaccharide amount and structure. Total (1,3;1,4)-β-glucan ranged from 0.06 to 0.43 (w/w) whilst internal cellotriose:cellotetraose ratios ranged from 1.8 to 2.9:1. Arabinoxylan amounts fell between 1.5 and 3.6 (w/w) and the arabinose:xylose ratio, denoting arabinoxylan structure, ranged from 0.95 to 1.35. The distribution of these and other cell wall polysaccharides varied across grain tissues as assessed by electron microscopy. When ten genotypes were tested across five environmental sites, genotype (G) was the dominant source of variation for both (1,3;1,4)-β-glucan and arabinoxylan content (69–74), with environment (E) responsible for 5–14. There was a small G × E effect for both polysaccharides. This study defines the amount and spatial distribution of polysaccharides and reveals a significant genetic influence on cell wall composition in sorghum grain.

Efficient eucalypt cell wall deconstruction and conversion for sustainable lignocellulosic biofuels

In order to meet the world’s growing energy demand and reduce the impact of greenhouse gas emissions resulting from fossil fuel combustion, renewable plant-based feedstocks for biofuel production must be considered. The first-generation biofuels, derived from starches of edible feedstocks, such as corn, create competition between food and fuel resources, both for the crop itself and the land on which it is grown. As such, biofuel synthesized from non-edible plant biomass (lignocellulose) generated on marginal agricultural land will help to alleviate this competition. Eucalypts, the broadly defined taxa encompassing over 900 species of Eucalyptus, Corymbia, and Angophora are the most widely planted hardwood tree in the world, harvested mainly for timber, pulp and paper, and biomaterial products. More recently, due to their exceptional growth rate and amenability to grow under a wide range of environmental conditions, eucalypts are a leading option for the development of a sustainable lignocellulosic biofuels. However, efficient conversion of woody biomass into fermentable monomeric sugars is largely dependent on pretreatment of the cell wall, whose formation and complexity lend itself toward natural recalcitrance against its efficient deconstruction. A greater understanding of this complexity within the context of various pretreatments will allow the design of new and effective deconstruction processes for bioenergy production. In this review, we present the various pretreatment options for eucalypts, including research into understanding structure and formation of the eucalypt cell wall.

Surface Proteins of Lactobacillus crispatus: Adhesive Properties and Cell Wall Anchoring

Bacterial surface-associated proteins are important in communication with the environment and bacteria-host interactions. In this thesis work, surface molecules of Lactobacillus crispatus important in host interaction were studied. The L. crispatus strains of the study were known from previous studies to be efficient in adhesion to intestinal tract and ECM. L. crispatus JCM 5810 possess an adhesive surface layer (S-layer) protein, whose functions and domain structure was characterized. We cloned two S-layer protein genes (cbsA; collagen-binding S-layer protein A and silent cbsB) and identified the protein region in CbsA important for adhesion to host tissues, for polymerization into a periodic layer as well as for attachment to the bacterial cell surface. The analysis was done by extensive mutation analysis and by testing His6-tagged fusion proteins from recombinant Escherichia coli as well as by expressing truncated CbsA peptides on the surface of Lactobacillus casei. The N-terminal region (31-274) of CbsA showed efficient and specific binding to collagens, laminin and extracellular matrix on tissue sections of chicken intestine. The N-terminal region also contained the information for formation of periodic S-layer polymer. This region is bordered at both ends by a conserved short region rich in valines, whose substitution to leucines drastically affected the periodic polymer structure. The mutated CbsA proteins that failed to form a periodic polymer, did not bind collagens, which indicates that the polymerized structure of CbsA is needed for collagen-binding ability. The C-terminal region, which is highly identical in S-layer proteins of L. crispatus, Lactobacillus acidophilus and Lactobacillus helveticus, was shown to anchor the protein to the bacterial cell wall. The C-terminal CbsA peptide specifically bound to bacterial teichoic acid and lipoteichoic acids. In conclusion, the N-terminal domain of the S-layer protein of L. crispatus is important for polymerization and adhesion to host tissues, whereas the C-terminal domain anchors the protein to bacterial cell-wall teichoic acids. Lactobacilli are fermentative organisms that effectively lower the surrounding pH. While this study was in progress, plasminogen-binding proteins enolase and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) were identified in the extracellular proteome of L. crispatus ST1. In this work, the cell-wall association of enolase and GAPDH were shown to rely on pH-reversible binding to the cell-wall lipoteichoic acids. Enolase from L. crispatus was functionally compared with enolase from L. johnsonii as well as from pathogenic streptococci (Streptococcus pneumoniae, Streptococcus pyogenes) and Staphylococcus aureus. His6-enolases from commensal lactobacilli bound human plasminogen and enhanced its activation by human plasminogen activators similarly to, or even better than, the enolases from pathogens. Similarly, the His6-enolases from lactobacilli exhibited adhesive characteristics previously assigned to pathogens. The results call for more detailed analyses of the role of the host plasminogen system in bacterial pathogenesis and commensalism as well of the biological role and potential health risk of the extracellular proteome in lactobacilli.

A Mycobacterial Cyclic AMP Phosphodiesterase That Moonlights as a Modifier of Cell Wall Permeability

Mycobacterium tuberculosis utilizes many mechanisms to establish itself within the macrophage, and bacterially derived cAMP is important in modulating the host cellular response. Although the genome of M. tuberculosis is endowed with a number of mammalian-like adenylyl cyclases, only a single cAMP phosphodiesterase has been identified that can decrease levels of cAMP produced by the bacterium. We present the crystal structure of the full-length and sole cAMP phosphodiesterase, Rv0805, found in M. tuberculosis, whose orthologs are present only in /the genomes of slow growing and pathogenic mycobacteria. The dimeric core catalytic domain of Rv0805 adopts a metallophosphoesterase fold, and the C-terminal region builds the active site and contributes to multiple substrate utilization.Localization of Rv0805 to the cell wall is dependent on its C terminus, and expression of either wild type or mutationally inactivated Rv0805 in M. smegmatis alters cell permeability to hydrophobic cytotoxic compounds. Rv0805 may therefore play a key role in the pathogenicity of mycobacteria, not only by hydrolyzing bacterial cAMP, but also by moonlighting as a protein that can alter cell wall functioning.

Studies on the Cell Wall Structure and on the Mechanical Properties of Norway Spruce

The structure and the mechanical properties of wood of Norway spruce (Picea abies [L.] Karst.) were studied using small samples from Finland and Sweden. X-ray diffraction (XRD) was used to determine the orientation of cellulose microfibrils (microfibril angle, MFA), the dimensions of cellulose crystallites and the average shape of the cell cross-section. X-ray attenuation and x-ray fluorescence measurements were used to study the chemical composition and the trace element content. Tensile testing with in situ XRD was used to characterise the mechanical properties of wood and the deformation of crystalline cellulose within the wood cell walls. Cellulose crystallites were found to be 192 284 Å long and 28.9 33.4 Å wide in chemically untreated wood and they were longer and wider in mature wood than in juvenile wood. The MFA distribution of individual Norway spruce tracheids and larger samples was asymmetric. In individual cell walls, the mean MFA was 19 30 degrees, while the mode of the MFA distribution was 7 21 degrees. Both the mean MFA and the mode of the MFA distribution decreased as a function of the annual ring. Tangential cell walls exhibited smaller mean MFA and mode of the MFA distribution than radial cell walls. Maceration of wood material caused narrowing of the MFA distribution and removed contributions observed at around 90 degrees. In wood of both untreated and fertilised trees, the average shape of the cell cross-section changed from circular via ambiguous to rectangular as the cambial age increased. The average shape of the cell cross-section and the MFA distribution did not change as a result of fertilisation. The mass absorption coefficient for x-rays was higher in wood of fertilised trees than in that of untreated trees and wood of fertilised trees contained more of the elements S, Cl, and K, but a smaller amount of Mn. Cellulose crystallites were longer in wood of fertilised trees than in that of untreated trees. Kraft cooking caused widening and shortening of the cellulose crystallites. Tensile tests parallel to the cells showed that if the mean MFA is initially around 10 degrees or smaller, no systematic changes occur in the MFA distribution due to strain. The role of mean MFA in defining the tensile strength or the modulus of elasticity of wood was not as dominant as that reported earlier. Crystalline cellulose elongated much less than the entire samples. The Poisson ratio νca of crystalline cellulose in Norway spruce wood was shown to be largely dependent on the surroundings of crystalline cellulose in the cell wall, varying between -1.2 and 0.8. The Poisson ratio was negative in kraft cooked wood and positive in chemically untreated wood. In chemically untreated wood, νca was larger in mature wood and in latewood compared to juvenile wood and earlywood.

The key enzyme in galactose metabolism, UDP-galactose-4-epimerase, affects cell-wall integrity and morphology in Candida albicans even in the absence of galactose

The enzyme UDP-galactose-4-epimerase (GAL10) catalyzes a key step in galactose metabolism converting UDP-galactose to UDPglucose which then can get metabolized through glycolysis and TCA cycle thus allowing the cell to use galactose as a carbon and energy source. As in many fungi, a functional homolog of GAL10 exists in Candida albicans. The domainal organization of the homologs from Saccharomyces cerevisiae and C albicans show high degree of homology having both mutarotase and an epimerase domain. The former is responsible for the conversion of beta-D-galactose to alpha-D-galactose and the hitter for epimerization of UDP-galactose to UDP-glucose. Absence of C albicans GAL10 (CaGAL10) affects cell-wall organization, oxidative stress response, biofilm formation and filamentation. Cagal10 mutant cells tend to flocculate extensively as compared to the wild-type cells. The excessive filamentation in this mutant is reflected in its irregular and wrinkled colony morphology. Cagal10 strain is more susceptible to oxidative stress when tested in presence of H2O2. While the S. cerevsiae GAL10 (ScGAL10), essential for survival in the presence of galactose, has not been reported to have defects in the absence of galactose, the C albicans homolog shows these phenotypes during growth in the absence of galactose. Thus a functional CaGal10 is required not only for galactose metabolism but also for normal hyphal morphogenesis, colony morphology, maintenance of cell-wall integrity and for resistance to oxidative stress even in the absence of galactose. (c) 2006 Elsevier Inc. All rights reserved.

A study of the nanostructure of the cell wall of the tracheids of conifer xylem by x-ray scattering

The purpose of this study was to develop practical and reliable x-ray scattering methods to study the nanostructure of the wood cell wall and to use these methods to systematically study the nanostructure of Norway spruce and Scots pine grown in Finland and Sweden. Methods to determine the microfibril angle (MFA) distribution, the crystallinity of wood, and the average size of cellulose crystallites using wide-angle x-ray scattering were developed and these parameters were determined as a function of the number of the year ring. The mean MFA in Norway spruce decreases rapidly as a function of the number of the year ring and after the 7th year ring it varies between 6° and 10°. The mean MFA of Scots pine behaves the same way as the mean MFA of Norway spruce. The thickness of cellulose crystallites for Norway spruce and Scots pine appears to be constant as a function of the number of the year ring. The obtained mean values are 32 Å for Norway spruce and 31 Å for Scots pine. The length of the cellulose crystallites was also quite constant as a function of the year ring. The mean length of the crystallites for Norway spruce was 364 Å, while the standard deviation was 27 Å. The mass fraction of crystalline cellulose in wood is the crystallinity of wood and the intrinsic crystallinity of cellulose is the crystallinity of cellulose. The crystallinity of wood increases from the 2nd year ring to the 10th year ring from the pith and is constant after the 10th year ring. The crystallinity of cellulose obtained using nuclear magnetic resonance spectroscopy was 52% for both species. The crystallinity of wood and the crystallinity of cellulose behave the same way in Norway spruce and Scots pine. The methods were also applied to studies on thermally modified Scots pine wood grown in Finland. Wood is modified thermally by heating and steaming in order to improve its properties such as biological resistance and dimensional stability. Modification temperatures varied from 100 °C to 240 °C. The thermal modification increases the crystallinity of wood and the thickness of cellulose crystallites but does not influence the MFA distribution. When the modification temperature was 230 °C and time 4 h, the thickness of the cellulose crystallites increased from 31 Å to 34 Å.

Moonlighting Proteins of Lactobacillus crispatus : Extracellular Localization, Cell Wall Anchoring and Interactions with the Host

Moonlighting functions have been described for several proteins previously thought to localize exclusively in the cytoplasm of bacterial or eukaryotic cells. Moonlighting proteins usually perform conserved functions, e. g. in glycolysis or as chaperonins, and their traditional and moonlighting function(s) usually localize to different cell compartments. The most characterized moonlighting proteins in Grampositive bacteria are the glycolytic enzymes enolase and glyceraldehyde-3-phosphate dehydrogenase (GAPDH), which function in bacteria-host interactions, e. g. as adhesins or plasminogen receptors. Research on bacterial moonlighting proteins has focused on Gram-positive bacterial pathogens, where many of their functions have been associated with bacterial virulence. In this thesis work I show that also species of the genus Lactobacillus have moonlighting proteins that carry out functions earlier associated with bacterial virulence only. I identified enolase, GAPDH, glutamine synthetase (GS), and glucose-6-phosphate isomerase (GPI) as moonlighting proteins of Lactobacillus crispatus strain ST1 and demonstrated that they are associated with cell surface and easily released from the cell surface into incubation buffer. I also showed that these lactobacillar proteins moonlight either as adhesins with affinity for basement membrane and extracellular matrix proteins or as plasminogen receptors. The mechanisms of surface translocation and anchoring of bacterial moonlighting proteins have remained enigmatic. In this work, the surface localization of enolase, GAPDH, GS and GPI was shown to depend on environmental factors. The members of the genus Lactobacillus are fermentative organisms that lower the ambient pH by producing lactic acid. At acidic pH enolase, GAPDH, GS and GPI were associated with the cell surface, whereas at neutral pH they were released into the buffer. The release did not involve de novo protein synthesis. I showed that purified recombinant His6-enolase, His6-GAPDH, His6-GS and His6-GPI reassociate with cell wall and bind in vitro to lipoteichoic acids at acidic pH. The in-vitro binding of these proteins localizes to cell division septa and cell poles. I also show that the release of moonlighting proteins is enhanced in the presence of cathelicidin LL- 37, which is an antimicrobial peptide and a central part of the innate immunity defence. I found that the LL-37-induced detachment of moonlighting proteins from cell surface is associated with cell wall permeabilization by LL-37. The results in this thesis work are compatible with the hypothesis that the moonlighting proteins of L. crispatus associate to the cell wall via electrostatic or ionic interactions and that they are released into surroundings in stress conditions. Their surface translocation is, at least in part, a result from their release from dead or permeabilized cells and subsequent reassociation onto the cell wall. The results of this thesis show that lactobacillar cells rapidly change their surface architecture in response to environmental factors and that these changes influence bacterial interactions with the host.