Comparison of the fouling release properties of hydrophobic fluorinated and hydrophilic PEGylated block copolymer surfaces: attachment strength of the diatom Navicula and the green alga Ulva

To understand the role of surface wettability in adhesion of cells, the attachment of two different marine algae was studied on hydrophobic and hydrophilic polymer surfaces. Adhesion of cells of the diatom Navicula and sporelings (young plants) of the green macroalga Ulva to an underwater surface is mainly by interactions between the surface and the adhesive exopolymers, which the cells secrete upon settlement and during subsequent colonization and growth. Two types of block copolymers, one with poly(ethylene glycol) side-chains and the other with liquid crystalline, fluorinated side-chains, were used to prepare the hydrophilic and hydrophobic surfaces, respectively. The formation of a liquid crystalline smectic phase in the latter inhibited molecular reorganization at the surface, which is generally an issue when a highly hydrophobic surface is in contact with water. The adhesion strength was assessed by the fraction of settled cells (Navicula) or biomass (Ulva) that detached from the surface in a water flow channel with a wall shear stress of 53 Pa. The two species exhibited opposite adhesion behavior on the same sets of surfaces. While Navicula cells released more easily from hydrophilic surfaces, Ulva sporelings showed higher removal from hydrophobic surfaces. This highlights the importance of differences in cell-surface interactions in determining the strength of adhesion of cells to substrates.     

Structural basis for the recognition of the FapydG lesion (2,6-diamino-4-hydroxy-5-formamidopyrimidine) by formamidopyrimidine-DNA glycosylase

Formamidopyrimidine-DNA glycosylase (Fpg) is a DNA repair enzyme that excises oxidized purines such as 7,8-dihydro-8-oxoguanine (8-oxoG) and 2,6-diamino-4-hydroxy-5-formamidopyrimidine (FapyG) from damaged DNA. Here, we report the crystal structure of the Fpg protein from Lactococcus lactis (LlFpg) bound to a carbocyclic FapydG (cFapydG)-containing DNA. The structure reveals that Fpg stabilizes the cFapydG nucleoside into an extrahelical conformation inside its substrate binding pocket. In contrast to the recognition of the 8-oxodG lesion, which is bound with the glycosidic bond in a syn conformation, the cFapydG lesion displays in the complex an anti conformation. Furthermore, Fpg establishes interactions with all the functional groups of the FapyG base lesion, which can be classified in two categories: (i) those specifying a purine-derived lesion (here a guanine) involved in the Watson-Crick face recognition of the lesion and probably contributing to an optimal orientation of the pyrimidine ring moiety in the binding pocket and (ii) those specifying the imidazole ring-opened moiety of FapyG and probably participating also in the rotameric selection of the FapydG nucleobase. These interactions involve strictly conserved Fpg residues and structural water molecules mediated interactions. The significant differences between the Fpg recognition modes of 8-oxodG and FapydG provide new insights into the Fpg substrate specificity.     

Polyphyletic origin of pyrrolizidine alkaloids within the Asteraceae. Evidence from differential tissue expression of homospermidine synthase

The evolution of pathways within plant secondary metabolism has been studied by using the pyrrolizidine alkaloids (PAs) as a model system. PAs are constitutively produced by plants as a defense against herbivores. The occurrence of PAs is restricted to certain unrelated families within the angiosperms. Homospermidine synthase (HSS), the first specific enzyme in the biosynthesis of the necine base moiety of PAs, was originally recruited from deoxyhypusine synthase, an enzyme involved in the posttranslational activation of the eukaryotic initiation factor 5A. Recently, this gene recruitment has been shown to have occurred several times independently within the angiosperms and even twice within the Asteraceae. Here, we demonstrate that, within these two PA-producing tribes of the Asteraceae, namely Senecioneae and Eupatorieae, HSS is expressed differently despite catalyzing the same step in PA biosynthesis. Within Eupatorium cannabinum, HSS is expressed uniformly in all cells of the root cortex parenchyma, but not within the endodermis and exodermis. Within Senecio vernalis, HSS expression has been previously identified in groups of specialized cells of the endodermis and the adjacent root cortex parenchyma. This expression pattern was confirmed for Senecio jacobaea as well. Furthermore, the expression of HSS in E. cannabinum is dependent on the development of the plant, suggesting a close linkage to plant growth.     

Compensation for loss of ligand activity in surface plasmon resonance experiments

The determination of equilibrium binding constants is an important aspect of the analysis of protein-protein interactions. In recent years surface plasmon resonance experiments (e.g., with a BIAcore instrument) have provided a valuable experimental approach to determining such constants. The standard method is based on measuring amounts of analyte bound at equilibrium for different analyte concentrations. During the course of a typical surface plasmon resonance experiment the measured equilibrium levels for a given analyte concentration often decrease. This appears to be due to a loss of activity of the protein coupled to the sensor chip or other phenomena. The loss in signal can lead to an erroneous determination of the equilibrium constant. A data analysis approach is introduced that aims to compensate for the loss of activity so that its influence on the results of the experiments is reduced.     

Eudesmanolides from Calea trichomata

Chemical analysis of Calea trichomata yielded, besides four known eudesmanolides, a new eudesmanolide, trichomatolide A. The structure of the new compound was established by chemical and spectral methods.     

Eudesmanolides,trichomatolides B–E,and A heliangolide from Calea trichomata

Calea trichomata gave in addition to four known 1β-hydroxy-8β-tigloyloxy-11(13)-eudesmen-6α, 12-olide derivatives a new heliangolide, 3-deoxy     

Carbonic anhydrase heterozygosity and FST distributions in Kenyan baboon troops

An analysis of the distribution of carbonic anhydrase alleles in troops of olive baboons, Papio cynocephalus, is reported. In an earlier study (Olivier, T. J., J. Buettner-Janusch and V. Buettner-Janusch, 1974, Am. J. Phys. Anthrop., 41: 175–190) the authors found a significant excess of heterozygotes with a large amount of intertroop differentiation at the CA II locus. If balancing selection is acting on the CA II locus and maintaining an excess of heterozygotes, then the degree of local differentiation observed at this locus is unexpected. In this study the analyses of the CA I and CA II data are extended and some idiosyncratic features of baboon population structure are considered. Non-idealized forms of behavior, such as adult male migration and other age-specific and sex-specific behaviors, may affect observed patterns of gene frequency distributions. The analysis reveals that the excess of heterozygotes at the CA II locus is localized in the females only and that the males are highly differentiated among the troops. These findings suggest that a female-limited heterozygous advantage exists at the CA II locus in this baboon population. A computer simulation model, RAMBLE, further suggests that recurrent male migration between troops may explain the intertroop microdifferentiation found in primate populations.     

A family study of spontaneous sister chromatid exchange frequency.

The frequency of spontaneous sister chromatid exchanges (SCEs) was determined in PHA-stimulated peripheral lymphocytes of 52 individuals, comprising 12 complete 2-generation pedigrees. Neither intraindividual variation between replicate cultures established from the same blood sample nor variation among samples from the same individual initiated at different times was significant. However, familial factors affecting mean SCE frequencies were indicated by detection of significant differences among, but not within, families. Although sample sizes were small, a genetic contribution to the SCE frequency was suggested by the observed pattern of familial correlations.