Synergistic antifungal activity of two chitin-binding proteins from spindle tree (<Emphasis Type="Italic">Euonymus europaeus</Emphasis> L.)

Two structurally different chitin-binding proteins were isolated from bark and leaves of the spindle tree (Euonymus europaeus L.). Both the small hevein-like chitin-binding protein (Ee-CBP) and the classical class-I chitinase (Ee-chitinase) possess antifungal properties, Ee-CBP being far more potent than Ee-chitinase. In addition, Ee-CBP and Ee-chitinase display a pronounced synergistic effect when added together in the test medium. Determination of the biological activities indicates that the synergism between Ee-CBP and Ee-chitinase relies on a different mode of action. Cloning and sequencing of the corresponding genes further revealed that Ee-CBP and Ee-chitinase are simultaneously expressed in bark and leaf tissues, and hence can act synergistically in planta. Moreover, analysis of the deduced sequences allowed the exact relationship between the structurally different Ee-CBP and Ee-chitinase to be corroborated. Both proteins are synthesized as similar chimeric precursors consisting of an N-terminal hevein domain linked to a C-terminal chitinase-like domain by a hinge region. However, whereas in the case of Ee-chitinase the C-terminal chitinase domain remains linked to the N-terminal hevein domain, the corresponding domain is cleaved from the Ee-CBP-precursor resulting in the formation of the hevein-type Ee-CBP. Since both precursors are—apart from the hinge region between the hevein and chitinase domains—very similar, the Ee-CBP/Ee-chitinase system offers a unique opportunity to study the importance of sequence and/or structural information comprised in the hinge region for the posttranslational processing of the respective precursor proteins.Abbreviations AMP Antimicrobial protein - CBP Chitin-binding protein - GlcNAc N-Acetylglucosamine - HCA Hydrophobic cluster analysis - MeJA Methyl jasmonate - PDB Potato dextrose broth - RACE Rapid amplification of cDNA ends - SPR Surface plasmon resonance - UDA Urtica dioica agglutinin - WGA Wheat (Triticum aestivum) germ agglutinin     

Genetic variation in flowering time induces phenological assortative mating: quantitative genetic methods applied to Brassica rapa

It has been argued from first principles that plants mate assortatively by flowering time. However, there have been very few studies of phenological assortative mating, perhaps because current methods to infer paternal phenotype are difficult to apply to natural populations. Two methods are presented to estimate the phenotypic correlation between mates-the quantitative genetic metric for assortative mating-for phenological traits. The first method uses individual flowering schedules to estimate mating probabilities for every potential pairing in a sample. These probabilities are then incorporated into a weighted phenotypic correlation between all potential mates and thus yield a prospective estimate based on mating opportunities. The correlation between mates can also be estimated retrospectively by comparing the regression of offspring phenotype over one parent, which is inflated by assortative mating, to the regression over mid-parent, which is not. In a demonstration experiment with Brassica rapa, the prospective correlation between flowering times (days from germination to anthesis) of pollen recipients and their potential donors was 0.58. The retrospective estimate of this correlation strongly agreed with the prospective estimate. The prospective method is easily employed in field studies that explore the effect of phenological assortative mating on selection response and population differentiation.     

Mass spectrometry analysis of recombinant human ZP3 expressed in glycosylation-deficient CHO cells

The zona pellucida is an extracellular matrix that mediates taxon-specific fertilization in which human sperm will not bind to mouse eggs. The mouse zona pellucida is composed of three glycoproteins (ZP1, ZP2, ZP3). The primary structure of each has been deduced from the cDNA nucleic acid sequence, and each has been analyzed by mass spectrometry. However, determination of the secondary structure and processing of the human zona proteins have been hampered by the paucity of biological material. To investigate if taxon-specific sperm-egg recognition was ascribable to structural differences in a zona protein required for matrix formation, recombinant human ZP3 was expressed in CHO-Lec3.2.8.1 cells and compared to mouse ZP3. With nearly complete coverage, LC-QTOF mass spectrometry was used to determine the cleavage of an N-terminal signal peptide (amino acids 1-22) and the release of secreted ZP3 from a C-terminal transmembrane domain (amino acids 379-424). The resultant N-terminal glutamine was cyclized to pyroglutamate (pyrGln(23)), and several C-terminal peptides were detected, including one ending at Asn(350). The disulfide bond linkages of eight cysteine residues in the conserved zona domain were ascertained (Cys(46)/Cys(140), Cys(78)/Cys(99), Cys(217)/Cys(282), Cys(239)/Cys(300)), but the precise linkage of two additional disulfide bonds was indeterminate due to clustering of the remaining four cysteine residues (Cys(319), Cys(321), Cys(322), Cys(327)). Three of the four potential N-linked oligosaccharide binding sites (Asn(125), Asn(147), Asn(272)) were occupied, and clusters of O-glycans were observed within two regions, amino acids 156-173 and 260-281. Taken together, these data indicate that human and mouse ZP3 proteins are quite similar, and alternative explanations of taxon-specific sperm binding warrant exploration.     

Portability of oxidase domains in nonribosomal peptide synthetase modules

Oxazole and thiazole rings are present in numerous nonribosomal peptide natural products. Oxidase domains are responsible for catalyzing the oxidation of thiazolines and oxazolines to yield fully aromatic heterocycles. Unlike most domains, the placement of oxidase domains within assembly line modules varies. Noting this tolerance, we investigated the portability of an oxidase domain to a heterologous assembly line. The epimerase domain of PchE, involved in pyochelin biosynthesis, was replaced with the oxidase domain from MtaD, involved in myxothiazol biosynthesis. The chimeric module was expressed in soluble form as a flavin mononucleotide-containing flavoprotein. The functionality of the inserted oxidase domain was assayed within PchE and in transfer of the growing siderophore acyl chain from PchE to the next downstream module. While pyochelin-like product release was not observed downstream, the robust activity of the transplanted oxidase domain and the ability of the chimeric module to produce an advanced intermediate bound to the synthetase underscore the possibility of future engineering within nonribosomal peptide synthetase pathways using oxidase domains.     

Inhibition of the cell cycle is required for convergent extension of the paraxial mesoderm during Xenopus neurulation

Coordination of morphogenesis and cell proliferation is essential during development. In Xenopus, cell divisions are rapid and synchronous early in development but then slow and become spatially restricted during gastrulation and neurulation. One tissue that transiently stops dividing is the paraxial mesoderm, a dynamically mobile tissue that forms the somites and body musculature of the embryo. We have found that cessation of cell proliferation is required for the proper positioning and segmentation of the paraxial mesoderm as well as the complete elongation of the Xenopus embryo. Instrumental in this cell cycle arrest is Wee2, a Cdk inhibitory kinase that is expressed in the paraxial mesoderm from mid-gastrula stages onwards. Morpholino-mediated depletion of Wee2 increases the mitotic index of the paraxial mesoderm and this results in the failure of convergent extension and somitogenesis in this tissue. Similar defects are observed if the cell cycle is inappropriately advanced by other mechanisms. Thus, the low mitotic index of the paraxial mesoderm plays an essential function in the integrated cell movements and patterning of this tissue.