Analysis of structure and function of the giant protein Pf332 in Plasmodium falciparum

Virulence of Plasmodium falciparum , the most lethal parasitic disease in humans, results in part from adhesiveness and increased rigidity of infected erythrocytes. Pf332 is trafficked to the parasite-infected erythrocyte via Maurer's clefts, structures for protein sorting and export in the host erythrocyte. This protein has a domain similar to the Duffy-binding-like (DBL) domain, which functions by binding to receptors for adherence and invasion. To address structure of the Pf332 DBL domain, we expressed this region, and validated its fold on the basis of the disulphide bond pattern, which conformed to the generic pattern for DBL domains. The modelled structure for Pf332 DBL had differences compared with the erythrocyte-binding region of the αDBL domain of Plasmodium knowlesi Duffy-binding protein (Pkα-DBL). We addressed the function of Pf332 by constructing parasites that either lack expression of the protein or express an altered form. We found no evidence that Pf332 is involved in cytoadhesion or merozoite invasion. Truncation of Pf332 had a significant effect on deformability of the P. falciparum -infected erythrocyte, while loss of the full protein deletion did not. Our data suggest that Pf332 may contribute to the overall deformability of the P. falciparum -infected erythrocyte by anchoring and scaffolding.     

Distribution of Several Activating and Inhibitory Receptors on CD3<Superscript>−</Superscript>CD16<Superscript>+</Superscript> NK Cells and Their Correlation with NK Cell Function in Healthy Individuals

The aim of this study was to estimate the distribution and density of a representative set of activating and inhibitory receptors on gated natural killer (NK) cells, as well as on their bright and dim subsets, and to correlate the receptor expression with NK cell activity for healthy individuals on CD3⁻CD16⁺ NK cells. We show that in 43 healthy controls NK cell activity against K562 target cells was 37.34% (E:T, 80:1) by standard chromium release assay. The expression of receptors on NK cells and their subsets was analyzed by flow cytometry. The cytotoxic CD3⁻CD16^bright NK subset constituted 78.97%, while the regulatory CD3⁻CD16^dim NK subset constituted 21.03% of NK cells. We show the distribution of NKG2D, CD161, CD158a, and CD158b receptors on CD3⁻CD16⁺ NK cells in peripheral blood lymphocytes (PBLs), on gated NK cells, and on the CD3⁻CD16^bright and CD3⁻CD16^dim subsets. Contrary to CD158a and CD158b killer immunoglobulin-like receptors (KIRs), there is a significant positive correlation of NKG2D and CD161 expression with NK cytotoxicity. We show the kinetics of change in CD3⁻CD16⁺NK/K562 conjugate composition, together with the stronger target binding capacity of CD16^bright NK cells. Furthermore, we show that after coculture of PBLs with K562 the expression of CD107a, a degranulation marker, on CD3⁻CD16⁺NK cells and subsets is time dependent and significantly higher on the cytotoxic CD3⁻CD16^bright NK subset. The novel data obtained regarding expression of NK cell activating and inhibitory receptors for healthy individuals may aid in detecting changes that are associated with various diseases.     

Susceptibility to Crohn’s disease is mediated by <Emphasis Type="Italic">KIR</Emphasis>2DL2/<Emphasis Type="Italic">KIR</Emphasis>2DL3 heterozygosity and the HLA-C ligand

In the present study, we investigated the relationship between the KIR loci and the genes encoding their HLA ligands and genetic susceptibility to Crohn’s disease (CD). Analyses of the interactions between KIR3DL1, KIR2DL1, KIR2DL2, and KIR2DL3 with their respective HLA ligands indicate that there is a protective effect for KIR2DL2 in the absence of its HLA ligand C1. Given that KIR2DL2 and KIR2DL3 segregate as alleles, we compared their genotypic distributions to expectations under Hardy–Weinberg Equilibrium (HWE) with regard to the HLA ligand C1 status. While all the genotypic distributions conform to expectations under HWE in controls, in C2 ligand homozygous cases there is significant deviation from HWE, with a reduction of KIR2DL2, KIR2DL3 heterozygotes. KIR2DL2, KIR2DL3 heterozygosity is the only genotypic combination that confers protection from CD. In addition to the protective effect (OR = 0.44, CI = 0.22–0.87; p = 0.018) observed in C2 ligand homozygotes, the KIR2DL2, KIR2DL3 genotype is predisposing (OR = 1.34, CI = 1.03–4.53; p = 0.031) in the presence of C1 ligand. A test for trend of HLA class I C ligand group genotypes with KIR2DL2, KIR2DL3 heterozygosity in cases and controls indicates that C1, C2 ligand group heterozygotes have an intermediate effect on predisposition. These results show for the first time that disease susceptibility may be related to heterozygosity at a specific KIR locus, and that HLA ligand genotype influences the relative effect of the KIR genotype.     

Destruction of Deinococcus geothermalis biofilm by photocatalytic ALD and sol-gel TiO2 surfaces

The aim of the present work was to explore possibilities of photocatalytic TiO₂ coating for reducing biofilms on non-living surfaces. The model organism, Deinococcus geothermalis, known to initiate growth of durable, colored biofilms on machine surfaces in the paper industry, was allowed to form biofilms on stainless steel, glass and TiO₂ film coated glass or titanium. Field emission electron microscopy revealed that the cells in the biofilm formed at 45°C under vigorous shaking were connected to the surface by means of numerous adhesion threads of 0.1--0.3 μm in length. Adjacent cells were connected to one another by threads of 0.5--1 μm in length. An ultrastructural analysis gave no indication for the involvement of amorphous extracellular materials (e.g., slime) in the biofilm. When biofilms on photocatalytic TiO₂ surfaces, submerged in water, were exposed to 20 W h m⁻² of 360 nm light, both kinds of adhesion threads were completely destroyed and the D. geothermalis cells were extensively removed (from >10⁷ down to below 10⁶ cells cm⁻²). TiO₂ films prepared by the sol-gel technique were slightly more effective than those prepared by the ALD technique. Doping of the TiO₂ with sulfur did not enhance its biofilm-destroying capacity. The results show that photocatalytic TiO₂ surfaces have potential as a self-cleaning technology for warm water using industries.     

Photochemical mineralization of synthetic lignin in lake water indicates enhanced turnover of aromatic organic matter under solar radiation

The degradation of ¹⁴C-[ring]-labelled syntheticlignin (¹⁴C-DHP) and dissolved organic carbon(DOC) from lake water were studied simultaneously.¹⁴C-DHP was incubated in humic lake water (colour173 mg Pt l^-1) for 7 d in the dark or under solarradiation. In the dark <0.4% of the introduced¹⁴C-DHP label and 4% of the indigenous DOC weremineralized, indicating that the ¹⁴C-labelledaromatic rings of DHP and the humic DOC weremicrobiologically recalcitrant. Under solar radiation(116 MJ m^-2), 17–21% of the ¹⁴C-labelledcarbons in DHP and 18–23% of the indigenous DOC weremineralized in 7 d. Simultaneously the watersolubility of ¹⁴C-DHP increased. Solar radiationconverted the aromatic cores of synthetic lignin toCO₂ and soluble organic photoproducts. Theresults suggest that solar radiation plays a key rolein the decomposition of natural polyaromatic matter.     

Mutations in AXIN2 cause familial tooth agenesis and predispose to colorectal cancer

Wnt signaling regulates embryonic pattern formation and morphogenesis of most organs. Aberrations of regulation of Wnt signaling may lead to cancer. Here, we have used positional cloning to identify the causative mutation in a Finnish family in which severe permanent tooth agenesis (oligodontia) and colorectal neoplasia segregate with dominant inheritance. Eleven members of the family lacked at least eight permanent teeth, two of whom developed only three permanent teeth. Colorectal cancer or precancerous lesions of variable types were found in eight of the patients with oligodontia. We show that oligodontia and predisposition to cancer are caused by a nonsense mutation, Arg656Stop, in the Wnt-signaling regulator AXIN2. In addition, we identified a de novo frameshift mutation 1994-1995insG in AXIN2 in an unrelated young patient with severe tooth agenesis. Both mutations are expected to activate Wnt signaling. The results provide the first evidence of the importance of Wnt signaling for the development of dentition in humans and suggest that an intricate control of Wnt-signal activity is necessary for normal tooth development, since both inhibition and stimulation of Wnt signaling may lead to tooth agenesis. Our findings introduce a new gene for hereditary colorectal cancer and suggest that tooth agenesis may be an indicator of cancer susceptibility.     

On the dynamics of T-cell activation in lymph nodes

The immune system is a complex network comprising many different organs and cell types, all of which have to work together in a highly accurate manner to exert their function. How is it, then, that the key players of adaptive immunity, T cells, B cells and dendritic cells (DC) move through this network? How is compartmentalization maintained and how do they interact? Over the past decade much attention has been paid to how and where T-cell/DC interactions take place, but only recently--with the advent of new techniques--has research been directed to investigate 'live' T-cell/DC interactions ex vivo and in situ. Whereas the overall sequence of events leading to T-cell activation is largely undisputed, many of the cellular and molecular details of early T-cell priming remain undefined or controversial. This review will focus on recent findings and discuss their implications for T-cell activation.     

Utilization of dimeric lignin model compounds by mixed bacterial cultures

Summary The degradation of dimeric phenylpropanoid lignin model compounds using mixed bacterial cultures was studied. The six model compounds contained the most common linkages of lignin: -O-4, -, -5, and -1. The results indicate that it is possible to enrich bacteria which are able to degrade all these compounds. Bacteria were also able to use these dimers as the sole source of carbon for growth. In view of these results it seems probable that bacterial inability to degrade polymeric lignin is due to the physical properties such as the molecular size of lignin.     

Mitochondrial toxicity detected in a health product with a boar spermatozoan bioassay

Seaweed and organic alfalfa capsules sold as "health promoting" products had repeatedly caused emesis in a consumer. Using the boar spermatozoan bioassay, the capsule contents were found to contain a toxic substance that inhibited boar sperm motility and depolarised mitochondria at low exposure concentrations of 10 microg/ml. The capsule also contained high amounts (10(5)-10(7) cfu/g), of endospore-forming bacteria and Streptomyces-like bacteria. Bacteria from the capsule produced toxic substances when cultured in the laboratory. Three different toxic responses were provoked in the spermatozoa exposed to extracts from the Streptomyces-like isolates: a) hyperpolarisation of the plasma membrane and depolarisation of the mitochondria; b) depolarisation of mitochondria similar to that caused by the capsule content extract; and c) motility inhibition, with no observed change of any cytosolic transmembrane potential. Membrane potential changes in the sperm cells exposed to the bacterial extracts were similar to those provoked by exposure to valinomycin and bafilomycin A1, to nigericin, and to oligomycin and ionomycin, respectively. Extracts prepared from Bacillus isolated from the capsule non-specifically depolarised all the cellular transmembrane potentials. The results demonstrate the potential value of a cell toxicity assay with boar spermatozoa for detecting hazardous substances in products intended for human consumption, without whole-animal exposure or using fetal calf serum for cell cultures.