Synthase Catalytic Subunit Research Articles

Plant Cell Wall Dynamics in Compatible and Incompatible Potato Response to Infection Caused by Potato Virus Y (PVYNTN).

The cell wall provides the structure of the plant, and also acts as a barier against biotic stress. The vein necrosis strain of Potato virus Y (PVYNTN) induces necrotic disease symptoms that affect both plant growth and yield. Virus infection triggers a number of inducible basal defense responses, including defense proteins, especially those involved in cell wall metabolism. This study investigates the comparison of cell wall host dynamics induced in a compatible (potato cv. Irys) and incompatible (potato cv. Sárpo Mira with hypersensitive reaction gene Ny-Smira) PVYNTN–host–plant interaction. Ultrastructural analyses revealed numerous cell wall changes induced by virus infection. Furthermore, the localization of essential defensive wall-associated proteins in susceptible and resistant potato host to PVYNTN infection were investigated. The data revealed a higher level of detection of pathogenesis-related protein 2 (PR-2) in a compatible compared to an incompatible (HR) interaction. Immunofluorescence analyses indicated that hydroxyproline-rich glycoproteins (HRGP) (extensin) synthesis was induced, whereas that of cellulose synthase catalytic subunits (CesA4) decreased as a result of PVYNTN infection. The highest level of extensin localization was found in HR potato plants. Proteins involved in cell wall metabolism play a crucial role in the interaction because they affect the spread of the virus. Analysis of CesA4, PR-2 and HRGP deposition within the apoplast and symplast confirmed the active trafficking of these proteins as a step-in potato cell wall remodeling in response to PVYNTN infection. Therefore, cell wall reorganization may be regarded as an element of “signWALLing”—involving apoplast and symplast activation as a specific response to viruses.

Cellulose microfibril structure: inspirations from plant diversity

Cellulose microfibrils are synthesized at the plasma membrane by cellulose synthase catalytic subunits that associate to form cellulose synthesis complexes. Variation in the organization of these complexes underlies the variation in cellulose microfibril structure among diverse organisms. However, little is known about how the catalytic subunits interact to form complexes with different morphologies. We are using an evolutionary approach to investigate the roles of different catalytic subunit isoforms in organisms that have rosette-type cellulose synthesis complexes.

Chlorflavonin Targets Acetohydroxyacid Synthase Catalytic Subunit IlvB1 for Synergistic Killing of Mycobacterium tuberculosis.

The flavonoid natural compound chlorflavonin was isolated from the endophytic fungus Mucor irregularis, which was obtained from the Cameroonian medicinal plant Moringa stenopetala. Chlorflavonin exhibited strong growth inhibitory activity in vitro against Mycobacterium tuberculosis (MIC90 1.56 μM) while exhibiting no cytotoxicity toward the human cell lines MRC-5 and THP-1 up to concentrations of 100 μM. Mapping of resistance-mediating mutations employing whole-genome sequencing, chemical supplementation assays, and molecular docking studies as well as enzymatic characterization revealed that chlorflavonin specifically inhibits the acetohydroxyacid synthase catalytic subunit IlvB1, causing combined auxotrophies to branched-chain amino acids and to pantothenic acid. While exhibiting a bacteriostatic effect in monotreatment, chlorflavonin displayed synergistic effects with the first-line antibiotic isoniazid and particularly with delamanid, leading to a complete sterilization in liquid culture in combination treatment. Using a fluorescent reporter strain, intracellular activity of chlorflavonin against Mycobacterium tuberculosis inside infected macrophages was demonstrated and was superior to streptomycin treatment.

PhCESA3 silencing inhibits elongation and stimulates radial expansion in petunia

Cellulose synthase catalytic subunits (CESAs) play important roles in plant growth, development and disease resistance. Previous studies have shown an essential role of Arabidopsis thaliana CESA3 in plant growth. However, little is known about the role of CESA3 in species other than A. thaliana. To gain a better understanding of CESA3, the petunia (Petunia hybrida) PhCESA3 gene was isolated, and the role of PhCESA3 in plant growth was analyzed in a wide range of plants. PhCESA3 mRNA was present at varying levels in tissues examined. VIGS-mediated PhCESA3 silencing resulted in dwarfing of plant height, which was consistent with the phenotype of the A. thaliana rsw1 mutant (a temperature-sensitive allele of AtCESA1), the A. thaliana cev1 mutant (the AtCESA3 mild mutant), and the antisense AtCESA3 line. However, PhCESA3 silencing led to swollen stems, pedicels, filaments, styles and epidermal hairs as well as thickened leaves and corollas, which were not observed in the A. thaliana cev1 mutant, the rsw1 mutant and the antisense AtCESA3 line. Further micrographs showed that PhCESA3 silencing reduced the length and increased the width of cells, suggesting that PhCESA3 silencing inhibits elongation and stimulates radial expansion in petunia.

Proteomic analysis of differentially expressed proteins in the marine fish parasitic ciliate Cryptocaryon irritans

Cryptocaryoniasis is a severe disease of farmed marine fish caused by the parasitic ciliate Cryptocaryon irritans. This disease can lead to considerable economic loss, but studies on proteins linked to disease development and antigenic proteins for vaccine development have been relatively scarce to date. In this study, 53 protein spots with differential abundance, representing 12 proteins, were identified based on a pair-wise comparison among theronts, trophonts, and tomonts. Meanwhile, 33 protein spots that elicited serological responses in rabbits were identified, representing 9 proteins. In addition, 27 common antigenic protein spots reacted with grouper anti-sera, representing 10 proteins. Most of the identified proteins were involved in cytoskeletal and metabolic pathways. Among these proteins, actin and α-tubulin appeared in all three developmental stages with differences in molecular weights and isoelectric points; 4 proteins (vacuolar ATP synthase catalytic subunit α, mcm2-3-5 family protein, 26S proteasome subunit P45 family protein and dnaK protein) were highly expressed only in theronts; while protein kinase domain containing protein and heat shock protein 70 showed high levels of expression only in trophonts and tomonts, respectively. Moreover, actin was co-detected with 3 rabbit anti-sera while β-tubulin, V-type ATPase α subunit family protein, heat shock protein 70, mitochondrial-type hsp70, and dnaK proteins showed immunoreactivity with corresponding rabbit anti-sera in theronts, trophonts, and tomonts. Furthermore, β-tubulin, the metabolic-related protein enolase, NADH-ubiquinone oxidoreductase 75kDa subunit, malate dehydrogenase, as well as polypyrimidine tract-binding protein, glutamine synthetase, protein kinase domain containing protein, TNFR/NGFR cysteine-rich region family protein, and vacuolar ATP synthase catalytic subunit α, were commonly detected by grouper anti-sera. Therefore, these findings could contribute to an understanding of the differences in gene expression and phenotypes among the different stages of parasitic infection, and might be considered as a source of candidate proteins for disease diagnosis and vaccine development.

Skeletal Muscle β‐F1‐ATPase Translation is Inhibited by Hyperlipidemia‐Induced miR‐127‐5p Expression in Human Obesity

We recently discovered persistent downregulation of the H+‐ATP synthase catalytic subunit (β‐F1‐ATPase) in skeletal muscle of obese individuals, which was linked to comorbid hyperlipidemia. β‐F1‐ATPase expression is primarily regulated post‐transcription, i.e. miRNAs, but the precise mechanism impeding expression are unclear. We tested the hypothesis that hyperlipidemia reduces β‐F1‐ATPase translational efficiency and is mediated by miR‐127‐5p, a miRNA known to control β‐F1‐ATPase translation. Biopsies isolated from the vastus lateralis of lean (BMI蠄25; n=7) and obese (BMI蠅30; n=6) subjects were evaluated for mRNA/miRNA expression via qRT‐PCR, protein by Western blot, and translation efficiency was calculated as the mRNA/protein ratio. Our results confirmed β‐F1‐ATPase translation was lower in obese individuals (P<0.01; 0.25±0.05%) compared to healthy weight controls (0.59±0.09%), and correlated with miR‐127‐5p expression (P<0.01; r=‐0.67). Bisulfite sequencing analysis of the miR‐127‐5p promoter revealed two hypomethylated sites in obese individuals, which may sustain an upregulation. Moreover, we found miR‐127‐5p present in muscle‐derived blood exosomes suggesting putative involvement in intracellular cross‐talk. In primary myotubes from a lean volunteer, prolonged fatty acid exposure increased miR‐127‐5p expression. Free Fatty Acid (mEq/L) Unsaturated/ Saturated mRNA (2‐DDCt) Protein (AU) Translation (%) CTRL 0.347 ‐ 1.70±0.113 0.216±0.062 0.130±0.040 Lo Fat 0.185 0.55 1.60±0.094 0.202±0.038 0.123±0.008 Hi Fat 0.251 2.29 1.35±0.133* 0.095±0.006* 0.073±0.010 Hi Fat 0.269 0.54 1.66±0.145 0.093±0.003* 0.050±0.004* *P<0.05; One‐way ANOVA, Tukey9s posttest Inhibiting miR‐127‐5p with locked nucleic acids dose‐dependently improved β‐F1‐ATPase translation. Inhibitor (nM) mRNA (2‐DDCt) Protein (AU) Translation (%) 0 1.84±0.314 0.22±0.062 0.647±0.120 10 1.93±0.387 1.24±0.135* 0.500±0.148 50 2.00±0.498 1.24±0.242** 1.483±0.233* 100 1.76±0.207 1.54±0.086* 0.892±0.096 *P<0.05; **P<0.01; ***P<0.001; 1‐way ANOVA, Tukey9s posttest Our results provide evidence implicating hyperlipidemia‐induced miR‐127‐5p expression in suppressing β‐F1‐ATPase translation in human obesity.Funding from NIH/NIDDK grant DK094062 to CSK

Catalytic subunit stoichiometry within the cellulose synthase complex.

Cellulose synthesis is driven by large plasma membrane-inserted protein complexes, which in plants have 6-fold symmetry. In Arabidopsis (Arabidopsis thaliana), functional cellulose synthesis complexes (CSCs) are composed of at least three different cellulose synthase catalytic subunits (CESAs), but the actual ratio of the CESA isoforms within the CSCs remains unresolved. In this work, the stoichiometry of the CESAs in the primary cell wall CSC was determined, after elimination of CESA redundancy in a mutant background, by coimmunoprecipitation and mass spectrometry using label-free quantitative methods. Based on spectral counting, we show that CESA1, CESA3, and CESA6 are present in a 1:1:1 molecular ratio.

Eight distinct cellulose synthase catalytic subunit genes from Betula luminifera are associated with primary and secondary cell wall biosynthesis

Cellulose, a significant proportion of the plant cell wall, is the main determining factor of the wood qualities of a timber tree. Cellulose synthase (CESA), an essential catalyst for cellulose biosynthesis, is encoded by the CesA gene family. We isolated eight full-length CesA cDNAs from Betula luminifera on the basis of transcriptome sequencing. The predicted proteins comprised 985–1,103 amino acids, sharing 85–92 % identity with the corresponding PtiCESAs from Populus trichocarpa. Each protein contained typical motifs of plant CESA proteins. Phylogenetic analysis showed that BlCESA1, BlCESA3 and BlCESA4 belonged to three clades linked to secondary cell wall synthesis, and BlCESA2, BlCESA5, BlCESA6, BlCESA7 and BlCESA8 belonged to three clades associated with primary cell wall synthesis. Quantitative reverse transcription PCR and in situ mRNA hybridization indicated that transcripts of BlCesA1, BlCesA3 and BlCesA4 were most abundant in the xylem of the lignified stem and had similar expression patterns when treated with hormones and sucrose. Thus, the proteins encoded by these three genes might be subunits of the secondary wall CesA complex. However, the expression patterns of BlCesA1, BlCesA3 and BlCesA4 were different in response to mechanical stress. These three genes showed much higher expression levels in the tension wood than in the control, and they showed different expression patterns in the opposite wood, suggesting that these genes play different roles during secondary wall formation. BlCesA2, BlCesA5, BlCesA6 and BlCesA7 were predominantly expressed in the leaf and phloem. BlCesA8, which is most similar to BlCesA6, was strongly expressed in the leaf, phloem and cambium. Interestingly, these two genes showed distinct expression patterns when treated with hormones, sucrose and bending. Thus, in addition to biosynthesis of the primary cell wall, BlCesA8 might have other functions.

Effect of uracil addition on proteomic profiles and 1,3‐‐glucan production in Agrobacterium sp.

Uridine diphosphate (UDP)-glucose is a precursor of 1,3-β-glucan and is synthesized from glucose-1-phosphate and uridine triphosphate (UTP). Uracil was used as a precursor for UTP, which resulted in an increase in both the UDP-glucose level and the rate of 1,3-β-glucan synthesis. 1,3-β-Glucan production metabolism was reactivated after uracil addition during fermentation. 2D-PAGE was used to examine the changes in the expression level of the key metabolic enzymes in the production of 1,3-β-glucan after uracil addition. The results showed that the expression levels of UTP-glucose-1-phosphate uridylytransferase, phosphoglucomutase, and 1,3-β-glucan synthase catalytic subunit, key metabolic enzymes in the curdlan biosynthesis pathway, were increased after uracil addition by 3.5%, 30%, and 35%, respectively. Uracil phosphoribosyltransferase, which converts uracil to uridine monophosphate (UMP), was also upregulated 79% more than that without uracil addition. However, the expression levels of orotidine 5-phosphate decarboxylase, glucose-1-phosphate adenylyltransferase, and glucose-6-phosphate isomerase were decreased after uracil addition. This proteomic information is useful for predicting changes in the pathway of uracil utilization. This work provides proteomic information for the integrative analysis of bioinformatic databases, which can be used to predict and understand the metabolism of glucan synthesis at the cellular level.

Identification of Salmonella enterica genes with a role in persistence on lettuce leaves during cold storage by recombinase-based in vivo expression technology.

Recurrent outbreaks of enteric illness linked to lettuce and a lack of efficacious strategies to decontaminate produce underscores the need for a better understanding of the molecular interactions of foodborne pathogens with plants. This study aimed at identifying Salmonella enterica genes involved in the persistence of this organism on post-harvest lettuce during cold storage using recombinase-based in vivo expression technology (RIVET). In total, 37 potentially induced loci were identified in four distinct screenings. Knockout mutations in eight upregulated genes revealed that four of them have a role in persistence of the pathogen in this system. These genes included stfC, bcsA, misL, and yidR, encoding a fimbrial outer membrane usher, a cellulose synthase catalytic subunit, an adhesin of the autotransporter family expressed from the Salmonella pathogenicity island-3, and a putative ATP/GTP-binding protein, respectively. bcsA, misL, and yidR but not stfC mutants were impaired also in attachment and biofilm formation, suggesting that these functions are required for survival of S. enterica on post-harvest lettuce. This is the first report that MisL, which has a role in Salmonella binding to fibronectin in animal hosts, is involved also in adhesion to plant tissue. Hence, our study uncovered a new plant attachment factor in Salmonella and demonstrates that RIVET is an effective approach for investigating human pathogen-plant interactions in a post-harvest leafy vegetable.

Cdc42 Explores the Cell Periphery for Mate Selection in Fission Yeast

How cells polarize in response to external cues is a fundamental biological problem. For mating, yeast cells orient growth toward the source of a pheromone gradient produced by cells of the opposite mating type. Polarized growth depends on the small GTPase Cdc42, a central eukaryotic polarity regulator that controls signaling, cytoskeleton polarization, and vesicle trafficking. However, the mechanisms of polarity establishment and mate selection in complex cellular environments are poorly understood. Here we show that, in fission yeast, low-level pheromone signaling promotes a novel polarization state, where active Cdc42, its GEF Scd1, and scaffold Scd2 form colocalizing dynamic zones that sample the periphery of the cell. Two direct Cdc42 effectors--actin cables marked by myosin V Myo52 and the exocyst complex labeled by Sec6 and Sec8--also dynamically colocalize with active Cdc42. However, these cells do not grow due to a block in the exocytosis of cell wall synthases Bgs1 and Bgs4. High-level pheromone stabilizes active Cdc42 zones and promotes cell wall synthase exocytosis and polarized growth. However, in the absence of prior low-level pheromone signaling, exploration fails, and cells polarize growth at cell poles by default. Consequently, these cells show altered partner choice, mating preferentially with sister rather than nonsister cells. Thus, Cdc42 exploration serves to orient growth for partner selection. This process may also promote genetic diversification.

Proteome analysis of the wild and YX-1 male sterile mutant anthers of wolfberry (Lycium barbarum L.).

Pollen development is disturbed in the early tetrad stage of the YX-1 male sterile mutant of wolfberry (Lycium barbarum L.). The present study aimed to identify differentially expressed anther proteins and to reveal their possible roles in pollen development and male sterility. To address this question, the proteomes of the wild-type (WT) and YX-1 mutant were compared. Approximately 1760 protein spots on two-dimensional differential gel electrophoresis (2D-DIGE) gels were detected. A number of proteins whose accumulation levels were altered in YX-1 compared with WT were identified by mass spectrometry and the NCBInr and Viridiplantae EST databases. Proteins down-regulated in YX-1 anthers include ascorbate peroxidase (APX), putative glutamine synthetase (GS), ATP synthase subunits, chalcone synthase (CHS), CHS-like, putative callose synthase catalytic subunit, cysteine protease, 5B protein, enoyl-ACP reductase, 14-3-3 protein and basic transcription factor 3 (BTF3). Meanwhile, activities of APX and GS, RNA expression levels of apx and atp synthase beta subunit were low in YX-1 anthers which correlated with the expression of male sterility. In addition, several carbohydrate metabolism-related and photosynthesis-related enzymes were also present at lower levels in the mutant anthers. In contrast, 26S proteasome regulatory subunits, cysteine protease inhibitor, putative S-phase Kinase association Protein 1(SKP1), and aspartic protease, were expressed at higher levels in YX-1 anthers relative to WT anthers. Regulation of wolfberry pollen development involves a complex network of differentially expressed genes. The present study lays the foundation for future investigations of gene function linked with wolfberry pollen development and male sterility.

Proteomic Characterization of Aspergillus fumigatus Treated with an Antifungal Coumarin for Identification of Novel Target Molecules of Key Pathways

A synthetic coumarin, N,N,N-triethyl-11-(4-methyl-2-oxo-2H-chromen-7-yloxy)-11-oxoundecan-1-aminium bromide (SCD-1), having potent activity against pathogenic Aspergilli (MIC90 15.62 μg/mL), was investigated to identify its molecular targets in the pathogen. The proteome of Aspergillus fumigatus was developed after treatment with sublethal doses of compound and analyzed. The results demonstrated 143 differentially expressed proteins on treatment with SCD-1. The expression of four proteins, namely cell division control protein, ubiquitin-like activating enzyme, vacuolar ATP synthase catalytic subunit A, and UTP-glucose-1-phosphate uridylyltransferase of A. fumigatus, was completely inhibited, whereas there were 13 newly expressed and 96 overexpressed proteins, mainly belonging to stress pathway. The treatment of A. fumigatus with SCD-1 also led to attenuation of proteins involved in cell replication and other important biosynthetic processes, including riboflavin biosynthesis, which has been pathogen-specific. In addition to key enzymatic players and antioxidants, nine hypothetical proteins were also identified, seven of which have been novel, being described for the first time. As no cellular functions have yet been described for these hypothetical proteins, their alteration in response to SCD-1 provides significant information about their putative roles in pathogen defense.

Reconstitution of high-level micafungin resistance detected in a clinical isolate of Candida glabrata identifies functional homozygosity in glucan synthase gene expression

A mechanism for the acquisition of high-level echinocandin resistance in Candida glabrata was investigated. FKS mutants were constructed to: determine whether clinically significant micafungin resistance requires a hot-spot mutation in FKS1 and a premature stop codon in FKS2, as was observed in a clinical isolate; select for variants with reduced susceptibility and locate mutations in FKS genes; and assess the roles of FKS1 and FKS2. A panel of FKS mutants was constructed using micafungin-susceptible parents by site-directed mutagenesis. Drug susceptibility, gene expression and glucan synthase activities were compared between mutants. Mutations acquired by selection were identified by DNA sequence analysis of FKS genes from selected variants. Single FKS deletants were constructed and their phenotypes examined. Introduction of the hot-spot mutation in FKS1 alone conferred an intermediate reduction in susceptibility, and the premature stop codon in FKS2 alone had no effect on susceptibility, while severely reduced susceptibility equivalent to that of the clinical isolate required both mutations. Exposure of susceptible strains to micafungin yielded variants with an intermediate reduction in susceptibility that possessed a hot-spot mutation in FKS1. Further exposure to micafungin yielded variants with severely reduced susceptibility that acquired various single mutations in FKS2. The phenotypes of Δfks1 and Δfks2 mutants indicate that the two FKS genes are functionally redundant, while deletion of both FKS1 and FKS2 conferred synthetic lethality. In the laboratory mutants of C. glabrata, clinically significant reduced susceptibility to micafungin required single nucleotide changes in both FKS1 and FKS2, and both genes encoded β-1,3-glucan synthase catalytic subunits.

Four alleles of AtCESA3 form an allelic series with respect to root phenotype in Arabidopsis thaliana

Plant cell shape is determined by the orientation of cellulose microfibrils in the primary cell wall. Consequently, mutations that affect genes encoding the enzymes responsible for the synthesis of cellulose, namely, the cellulose synthase catalytic subunits, can alter cell shape substantially, particularly in the roots of affected plants. The multiple response expansion1 (mre1) mutant of Arabidopsis thaliana results from a point mutation in the AtCESA3 gene, which encodes one of the three isoforms of the cellulose synthase catalytic subunit required for synthesis of cellulose in the primary cell wall. Phenotypic comparison of the mre1 mutant with three other alleles (ectopic lignification1-1, ectopic lignification1-2 and constitutive expression of vsp1) showed that these four alleles form an allelic series with respect to their root phenotypes, with mre1 being the weakest allele identified to date. These analyses demonstrated that sucrose affects a significant alteration of cell shape in the roots of these mutants and likely suppresses root cell division in them as well, and that the chemical aminoisobutyric acid can suppress these effects of sucrose. Interestingly, the cell walls in the roots of these four AtCESA3 alleles contain different percentages of cellulose, and these percentages correlate with the lengths of the roots and cortex cells in these roots when grown on media containing high levels of sucrose.

Cloning and characterization of homeologous cellulose synthase catalytic subunit 2 genes from allotetraploid cotton (Gossypium hirsutum L.)

Cellulose synthase catalytic subunits (CesAs) are the catalytic sites within a multisubunit complex for cellulose biosynthesis in plants. CesAs have been extensively studied in diploid plants, but are not well characterized in polyploid plants. Gossypium hirsutum is an allotetraploid cotton species producing over 90% of the world's cotton fibers. Although G. hirsutum CesAs (GhCesAs) are responsible for cellulose production in cotton fiber, very limited numbers of GhCesA genes have been identified. Here, we report isolating and characterizing a pair of homeologous CesA2 genes and their full-length cDNAs from allotetraploid cotton. The GhCesA2-AT gene from the A-subgenome and GhCesA2-DT gene from the D-subgenome were screened from a G. hirsutum BAC library. These genes shared 92% sequence similarity throughout the entire sequence. The coding sequences were nearly identical, and the deduced amino acid sequences from GhCesA2-AT (1,039 amino acids) and GhCesA2-DT (1,040 amino acids) were identical except four amino acids, whereas the noncoding sequences showed divergence. Sequence analyses showed that all exons of GhCesA2-AT contained consensus splice donor dinucleotides, but one exon in GhCesA2-DT contained nonconsensus splice donor dinucleotides. Although the nonconsensus splice donor dinucleotides were previously suggested to be involved in alternative splice or pseudogenization, our results showed that a majority of GhCesA2-AT and GhCesA2-DT transcripts consisted of functional and full-length transcripts with little evidence for alternative mRNA isoforms in developing cotton fibers. Expression analyses showed that GhCesA2-AT and GhCesA2-DT shared common temporal and spatial expression patterns, and they were highly and preferentially expressed during the cellulose biosynthesis stage in developing cotton fibers. The observations of higher expression levels of both GhCesA2-AT and GhCesA2-DT in developing fibers of one near-isogenic line (NIL) with higher fiber bundle strength over the other NIL with lower fiber bundle strength suggested that the differential expression of genes associated with secondary cell wall cellulose biosynthesis in developing fiber might affect cotton fiber properties.

Cloning, characterization and evaluation of potent inhibitors of Shigella sonnei acetohydroxyacid synthase catalytic subunit

Acetohydroxyacid synthase (AHAS) is a thiamin diphosphate (ThDP)- and flavin adenine dinucleotide (FAD)-dependent plant and microbial enzyme that catalyzes the first common step in the biosynthesis of essential amino acids such as leucine, isoleucine and valine. To identify strong potent inhibitors against Shigella sonnei (S. sonnei) AHAS, we cloned and characterized the catalytic subunit of S. sonnei AHAS and found two potent chemicals (KHG20612, KHG25240) that inhibit 87–93% S. sonnei AHAS activity at an inhibitor concentration of 100uM. The purified S. sonnei AHAS had a size of 65kDa on SDS-PAGE. The enzyme kinetics revealed that the enzyme has a Km of 8.01mM and a specific activity of 0.117U/mg. The cofactor activation constant (Ks) for ThDP and (Kc) for Mg++ were 0.01mM and 0.18mM, respectively. The dissociation constant (Kd) for ThDP was found to be 0.14mM by tryptophan fluorescence quenching. The inhibition kinetics of inhibitor KHG20612 revealed an un-competitive inhibition mode with a Kii of 2.65mM and an IC50 of 9.3μM, whereas KHG25240 was a non-competitive inhibitor with a Kii of 5.2mM, Kis of 1.62mM and an IC50 of 12.1μM. Based on the S. sonnei AHAS homology model structure, the docking of inhibitor KHG20612 is predicted to occur through hydrogen bonding with Met 257 at a 1.7Å distance with a low negative binding energy of −9.8kcal/mol. This current study provides an impetus for the development of a novel strong antibacterial agent targeting AHAS based on these potent inhibitor scaffolds.

Binding Specificity of the Recombinant Cytoplasmic Domain ofCordyceps militarisβ-1,3-Glucan Synthase Catalytic Subunit

The cytoplasmic domain of the medicinal mushroom Cordyceps militaris β-1,3-glucan synthase catalytic subunit Fks1 was expressed as a fusion protein with an N-terminal hexahistidine tag and glutathione S-transferase in an Escherichia coli cell-free translation system, and was assayed for binding specificity. The recombinant cytoplasmic domain bound specifically to UDP-agarose and lichenan (β-glucan), but not to ADP-agarose, GDP-agarose, or other carbohydrates.

Rice Brittle culm 6 encodes a dominant-negative form of CesA protein that perturbs cellulose synthesis in secondary cell walls

The brittle culm (bc) mutants of Gramineae plants having brittle skeletal structures are valuable materials for studying secondary cell walls. In contrast to other recessive bc mutants, rice Bc6 is a semi-dominant bc mutant with easily breakable plant bodies. In this study, the Bc6 gene was cloned by positional cloning. Bc6 encodes a cellulose synthase catalytic subunit, OsCesA9, and has a missense mutation in its highly conserved region. In culms of the Bc6 mutant, the proportion of cellulose was reduced by 38%, while that of hemicellulose was increased by 34%. Introduction of the semi-dominant Bc6 mutant gene into wild-type rice significantly reduced the percentage of cellulose, causing brittle phenotypes. Transmission electron microscopy analysis revealed that Bc6 mutation reduced the cell wall thickness of sclerenchymal cells in culms. In rice expressing a reporter construct, BC6 promoter activity was detected in the culms, nodes, and flowers, and was localized primarily in xylem tissues. This expression pattern was highly similar to that of BC1, which encodes a COBRA-like protein involved in cellulose synthesis in secondary cell walls in rice. These results indicate that BC6 is a secondary cell wall-specific CesA that plays an important role in proper deposition of cellulose in the secondary cell walls.

Functional analysis of Gossypium hirsutum cellulose synthase catalytic subunit 4 promoter in transgenic Arabidopsis and cotton tissues

Gossypium hirsutum cellulose synthase catalytic subunit 4 ( GhCesA4) plays an important role in cellulose biosynthesis during cotton fiber development. The transcript levels of GhCesA4 are significantly up-regulated as secondary cell wall cellulose is produced in developing cotton fibers. To understand the molecular mechanisms involved in transcriptional regulation of GhCesA4, β-glucuronidase (GUS) activity regulated by a GhCesA4 promoter (−2574/+56) or progressively deleted promoters were determined in both cotton tissues and transgenic Arabidopsis. The spatial regulation of GhCesA4 expression was similar between cotton tissues and transgenic Arabidopsis. GUS activity regulated by the GhCesA4 promoter (−2574/+56) was found in trichomes and root vascular tissues in both cotton and transgenic Arabidopsis. The −2574/−1824 region was responsible for up-regulation of GhCesA4 expression in trichomes and root vascular tissues in transgenic Arabidopsis. The −1824/−1355 region negatively regulated GhCesA4 expression in most Arabidopsis vascular tissues. For vascular expression in stems and leaves, the −898/−693 region was required. The −693/−320 region of the GhCesA4 promoter was necessary for basal expression of GhCesA4 in cotton roots as well as Arabidopsis roots. Exogenous phytohormonal treatments on transgenic Arabidopsis revealed that phytohormones may be involved in the differential regulation of GhCesA4 during cotton fiber development.